Psoas and Paraspinous Muscle Measurements on Computed Tomography Predict Mortality in European Americans with Type 2 Diabetes Mellitus

BACKGROUND

Appendicular skeletal muscle mass index and muscle attenuation (density) are negatively associated with mortality in European-derived populations.

OBJECTIVES

The present analyses assessed association between axial skeletal muscle density and muscle index with mortality in European Americans with type 2 diabetes mellitus (T2D).

DESIGN

Single-center observational study.

SETTING

Diabetes Heart Study.

PARTICIPANTS

839 European Americans with T2D.

METHODS

Computed tomography-measured psoas and paraspinous muscle mass index (cross sectional area/height2) and radiographic density (Hounsfield Units) were assessed in all participants. A Cox proportional hazards model was computed. The fully-adjusted model included covariates age, sex, body mass index, smoking, alcohol use, diabetes duration, insulin use, hormone replacement therapy (women), prevalent cardiovascular disease (CVD), hypertension, and coronary artery calcified atherosclerotic plaque mass score. Deaths were recorded in the National Death Index data through December 31, 2015.

RESULTS

Participants included 428 women and 411 men with median (25th, 75th quartile) age 62.8 (56.1, 69.1) years and diabetes duration 8.0 (5.0, 14.0) years. After 11.9 (9.4, 13.3) years of follow-up, 314 (37.4%) of participants were deceased. In the fully-adjusted model, psoas muscle density (hazard ratio [HR] 0.81, p<0.001), psoas muscle index (HR 0.82, p=0.008), and paraspinous muscle density (HR 0.85, p=0.003) were inversely associated with mortality. Paraspinous muscle index was not significantly associated with mortality (HR 0.90, p=0.08). Results did not differ significantly between men and women.

CONCLUSIONS

In addition to established risk factors for mortality and CVD, higher psoas muscle index, psoas muscle density, and paraspinous muscle density were significantly associated with lower all-cause mortality in European Americans with T2D.

Volumetric bone mineral density of the spine predicts mortality in African-American men with type 2 diabetes

The study showed that in African-American men with type 2 diabetes mellitus (T2D), vertebral volumetric bone mineral density (vBMD) predicts all-cause mortality, independent of other risk factors for death.

INTRODUCTION

Compared to European Americans, African Americans have lower rates of osteoporosis and higher rates of T2D. The relationships between BMD and fractures with mortality are unknown in this population. The aim of this study was to determine relationships between vertebral fractures and vertebral vBMD and mortality in African Americans with T2D.

METHODS

Associations between vertebral fractures and vBMD with all-cause mortality were examined in 675 participants with T2D (391 women and 284 men) in the African American-Diabetes Heart Study (AA-DHS). Lumbar and thoracic vBMD were measured using quantitative computed tomography (QCT). Vertebral fractures were assessed on sagittal CT images. Associations of vertebral fractures and vBMD with all-cause mortality were determined in sex-stratified analyses and in the full sample. Covariates in a minimally adjusted model included age, sex, BMI, smoking, and alcohol use; the full model was adjusted for those variables plus cardiovascular disease, hypertension, coronary artery calcified plaque, hormone replacement therapy (women), African ancestry proportion, and eGFR.

RESULTS

After mean 7.6 ± 1.8-year follow-up, 59 (15.1%) of women and 58 (20.4%) of men died. In men, vBMD was inversely associated with mortality in the fully adjusted model: lumbar hazard ratio (HR) per standard deviation (SD) = 0.70 (95% CI 0.52-0.95, p = 0.02) and thoracic HR per SD = 0.71 (95% CI 0.54-0.92, p = 0.01). Only trends toward association between vBMD and mortality were observed in the combined sample of men and women, as significant associations were absent in women. Vertebral fractures were not associated with mortality in either sex.

CONCLUSIONS

Lower vBMD was associated with increased all-cause mortality in African-American men with T2D, independent of other risk factors for mortality including subclinical atherosclerosis.

Increased intestinal permeability as a risk factor for type 2 diabetes

AIM

Relationships between the intestinal microbiota, intestinal permeability and inflammation in the context of risk for obesity-associated disease continue to be of interest. The aim of the study was to examine the associations between intestinal permeability and type 2 diabetes (T2D).

METHODS

A total of 130 individuals with T2D (age: 57.5±6.2 years (mean±SD); BMI: 30.4±3.2; 45% female) and 161 individuals without T2D (age: 37.4±12.5 years; BMI: 25.1±3.9; 65% female) were included in the study. Assessment of intestinal permeability included measurement of circulating lipopolysaccharide (LPS), LPS-binding protein (LBP) and intestinal fatty acid binding protein (iFABP) concentrations, which were used for calculation of a derived permeability risk score (PRS). Associations between permeability measures and T2D status were assessed using logistic regression models.

RESULTS

LBP (∼34%, P<0.001), iFABP (∼46%, P<0.001) and the PRS (∼24% P<0.001) were all significantly higher in the T2D affected individuals. Individuals with a PRS in the upper tertile were 5.07 times more likely (CI: 1.72-14.95; P=0.003) to have T2D when models were adjusted for age, sex and BMI. There was a trend towards improved prediction when including the PRS in models containing age, sex and BMI (AUC: 0.954 versus 0.962; P=0.06).

CONCLUSION

These data demonstrate differences in measures of intestinal permeability between individuals with and without T2D. The utility of using intestinal permeability measures as a tool for predicting T2D risk in at risk individuals should be further investigated.

Effects of Type 2 Diabetes on Brain Structure and Cognitive Function: African American-Diabetes Heart Study MIND

BACKGROUND AND PURPOSE

Rates of type 2 diabetes are higher among African Americans compared with individuals of European ancestry. The purpose of this investigation was to determine the relationship between MR imaging measures of brain structure (volume of GM, WM, WM lesions) and cognitive function in a population of African Americans with type 2 diabetes. These MR imaging measures of brain structure are affected by type 2 diabetes-associated macrovascular and microvascular disease and may be associated with performance on tasks of cognitive function in the understudied African American population.

MATERIALS AND METHODS

African Americans with type 2 diabetes enrolled in the African American-Diabetes Heart Study MIND study (n = 263) were evaluated across a broad range of cognitive domains and imaged with brain MR imaging. Associations between cognitive parameters and MR imaging measures of whole-brain GM, WM, and WM lesion volumes were assessed by using adjusted multivariate models.

RESULTS

Lower GM volume was associated with poorer performance on measures of general cognitive function, working memory, and executive function. Higher WM lesion volume was associated with poorer performance on a smaller subset of cognitive domains compared with GM volume but included aspects of working memory and executive function. There were no statistically significant associations with WM volume.

CONCLUSIONS

Markers of cortical atrophy and WM lesion volume are associated with cognitive function in African Americans with type 2 diabetes. These associations are described in an African American cohort with disease control similar to that of individuals of European ancestry, rather than underserved African Americans with poor access to health care. Interventions to reduce cortical atrophy and WM disease may improve cognitive outcomes in this understudied population.

Automated white matter total lesion volume segmentation in diabetes

BACKGROUND AND PURPOSE

WM lesion segmentation is often performed with the use of subjective rating scales because manual methods are laborious and tedious; however, automated methods are now available. We compared the performance of total lesion volume grading computed by use of an automated WM lesion segmentation algorithm with that of subjective rating scales and expert manual segmentation in a cohort of subjects with type 2 diabetes.

MATERIALS AND METHODS

Structural T1 and FLAIR MR imaging data from 50 subjects with diabetes (age, 67.7 ± 7.2 years) and 50 nondiabetic sibling pairs (age, 67.5 ± 9.4 years) were evaluated in an institutional review board-approved study. WM lesion segmentation maps and total lesion volume were generated for each subject by means of the Statistical Parametric Mapping (SPM8) Lesion Segmentation Toolbox. Subjective WM lesion grade was determined by means of a 0-9 rating scale by 2 readers. Ground-truth total lesion volume was determined by means of manual segmentation by experienced readers. Correlation analyses compared manual segmentation total lesion volume with automated and subjective evaluation methods.

RESULTS

Correlation between average lesion segmentation and ground-truth total lesion volume was 0.84. Maximum correlation between the Lesion Segmentation Toolbox and ground-truth total lesion volume (ρ = 0.87) occurred at the segmentation threshold of k = 0.25, whereas maximum correlation between subjective lesion segmentation and the Lesion Segmentation Toolbox (ρ = 0.73) occurred at k = 0.15. The difference between the 2 correlation estimates with ground-truth was not statistically significant. The lower segmentation threshold (0.15 versus 0.25) suggests that subjective raters overestimate WM lesion burden.

CONCLUSIONS

We validate the Lesion Segmentation Toolbox for determining total lesion volume in diabetes-enriched populations and compare it with a common subjective WM lesion rating scale. The Lesion Segmentation Toolbox is a readily available substitute for subjective WM lesion scoring in studies of diabetes and other populations with changes of leukoaraiosis.

Transferability and fine-mapping of glucose and insulin quantitative trait loci across populations: CARe, the Candidate Gene Association Resource

AIMS/HYPOTHESIS

Hyperglycaemia disproportionately affects African-Americans (AfAs). We tested the transferability of 18 single-nucleotide polymorphisms (SNPs) associated with glycaemic traits identified in European ancestry (EuA) populations in 5,984 non-diabetic AfAs.

METHODS

We meta-analysed SNP associations with fasting glucose (FG) or insulin (FI) in AfAs from five cohorts in the Candidate Gene Association Resource. We: (1) calculated allele frequency differences, variations in linkage disequilibrium (LD), fixation indices (F(st)s) and integrated haplotype scores (iHSs); (2) tested EuA SNPs in AfAs; and (3) interrogated within ± 250 kb around each EuA SNP in AfAs.

RESULTS

Allele frequency differences ranged from 0.6% to 54%. F(st) exceeded 0.15 at 6/16 loci, indicating modest population differentiation. All iHSs were <2, suggesting no recent positive selection. For 18 SNPs, all directions of effect were the same and 95% CIs of association overlapped when comparing EuA with AfA. For 17 of 18 loci, at least one SNP was nominally associated with FG in AfAs. Four loci were significantly associated with FG (GCK, p = 5.8 × 10(-8); MTNR1B, p = 8.5 × 10(-9); and FADS1, p = 2.2 × 10(-4)) or FI (GCKR, p = 5.9 × 10(-4)). At GCK and MTNR1B the EuA and AfA SNPs represented the same signal, while at FADS1, and GCKR, the EuA and best AfA SNPs were weakly correlated (r(2) <0.2), suggesting allelic heterogeneity for association with FG at these loci.

CONCLUSIONS/INTERPRETATION

Few glycaemic SNPs showed strict evidence of transferability from EuA to AfAs. Four loci were significantly associated in both AfAs and those with EuA after accounting for varying LD across ancestral groups, with new signals emerging to aid fine-mapping.

C-reactive protein concentration predicts mortality in type 2 diabetes: the Diabetes Heart Study

AIMS

Although current American Heart Association guidelines address C-reactive protein concentration and cardiovascular disease risk, it remains unclear whether this paradigm is consistent across populations with differing disease burdens. Individuals with Type 2 diabetes mellitus represent one group at increased risk of cardiovascular disease and subsequent mortality. This study aimed to examine the relationship between C-reactive protein concentrations and risk for all-cause mortality in European Americans with Type 2 diabetes from the Diabetes Heart Study.

METHODS

A total of 846 European Americans with Type 2 diabetes and baseline measures of C-reactive protein were evaluated. Vital status was determined after a follow-up period of 7.3 ± 2.1 years (mean ± SD). C-reactive protein concentrations were compared between living and deceased subgroups along with other known risk factors for cardiovascular disease, including blood lipids. Logistic regression was performed to determine risk for mortality associated with increasing C-reactive protein concentrations.

RESULTS

At follow-up 160 individuals (18.7%) were deceased. No significant differences in baseline serum glucose or lipid measures were observed between living and deceased subgroups. Baseline C-reactive protein concentrations were significantly higher in the deceased subgroup (9.37 ± 15.94) compared with the living subgroup (5.36 ± 7.91 mg/l; P < 0.0001). Participants with C-reactive protein concentrations of 3-10 mg/l were approximately two times more likely to be deceased at follow-up (OR 2.06; 95% CI 1.17-3.62); those with C-reactive protein >10 mg/l were more than five times more likely to be deceased (OR 5.24; CI 2.80-9.38).

CONCLUSIONS

This study documents the utility of C-reactive protein in predicting risk for all-cause mortality in European Americans with Type 2 diabetes and supports its use as a screening tool in risk prediction models.

Association of PNPLA3 SNP rs738409 with liver density in African Americans with type 2 diabetes mellitus

AIM

Non-alcoholic fatty liver disease (NAFLD) is commonly diagnosed in patients with obesity and type 2 diabetes mellitus (T2DM), and has been associated with the single nucleotide polymorphism (SNP) rs738409 in the PNPLA3 gene. This association remains to be investigated in African Americans with T2DM, a group at lower risk for hepatic steatosis relative to European Americans with T2DM.

METHODS

We examined 422 African Americans with T2DM (40.3% male; age: 56.4±9.6 years; Body Mass Index: 35.2±8.2 kg/m(2)), all with measures of liver density reflecting hepatic fat content on abdominal computed tomography, and blood glucose and lipid profiles. Associations between rs738409 and phenotypes of interest were determined using SOLAR, assuming an additive model of inheritance with covariates age, sex, BMI and use of lipid-lowering medications.

RESULTS

Mean±SD liver density was 55.4±10.2 Hounsfield Units. SNP rs738409 in PNPLA3 was significantly associated with liver density (P=0.0075) and hepatic steatosis (P=0.0350), but not with blood glucose, HbA(1c), total cholesterol, triglycerides, high-density or low-density lipoprotein levels or liver function tests (P=0.15-0.96).

CONCLUSION

These findings provide evidence that the PNPLA3 SNP rs738409 contributes to risk for increased liver fat content in African Americans with T2DM, an effect that appears to be independent from serum lipids. Although African Americans are less susceptible to fatty liver than European Americans, PNPLA3 appears to be a risk locus for hepatic steatosis in diabetic African Americans.

Analysis of FTO gene variants with obesity and glucose homeostasis measures in the multiethnic Insulin Resistance Atherosclerosis Study cohort

OBJECTIVE

Previous studies have replicated the association of variants within FTO (fat mass- and obesity-associated) intron 1 with obesity and adiposity quantitative traits in populations of European ancestry. Non-European populations, however, have not been so intensively studied. The goal of this investigation was to examine the association of FTO single-nucleotide polymorphisms (SNPs), prominent in the literature in a multiethnic sample of non-Hispanic White American (n=458), Hispanic American (n=373) and African American (n=288) subjects from the Insulin Resistance Atherosclerosis Study (IRAS). This cohort provides the unique ability to evaluate how variation within FTO influences measures of adiposity and glucose homeostasis in three different ethnicities, which were ascertained and examined using a common protocol.

DESIGN

A total of 26 FTO SNPs were genotyped, including those consistently associated in the literature (rs9939609, rs8050136, rs1121980, rs1421085, rs17817449 and rs3751812), and tested for association with adiposity and glucose homeostasis traits.

RESULTS

For the adiposity phenotypes, these and other SNPs were associated with body mass index (BMI) in both non-Hispanic Whites (P-values ranging from 0.015 to 0.048) and Hispanic Americans (P-values ranging from 7.1 × 10(-6) to 0.027). In Hispanic Americans, four other SNPs (rs8047395, rs10852521, rs8057044 and rs8044769) still showed evidence of association after multiple comparisons adjustment (P-values ranging from 5.0 × 10(-5) to 5.2 × 10(-4)). The historically associated BMI SNPs were not associated in the African Americans, but rs1108102 was associated with BMI (P-value of 5.4 × 10(-4)) after accounting for multiple comparisons. For glucose homeostasis traits, associations were seen with acute insulin response in non-Hispanic Whites and African Americans. However, all associations with glucose homeostasis measures were no longer significant after adjusting for multiple comparisons.

CONCLUSION

These results replicate the association of FTO intron 1 variants with BMI in non-Hispanic Whites and Hispanic Americans but show little evidence of association in African Americans, suggesting that the effect of FTO variants on adiposity phenotypes shows genetic heterogeneity dependent on ethnicity.

Candidate loci for insulin sensitivity and disposition index from a genome-wide association analysis of Hispanic participants in the Insulin Resistance Atherosclerosis (IRAS) Family Study

AIMS/HYPOTHESIS

The majority of type 2 diabetes genome-wide association studies (GWAS) to date have been performed in European-derived populations and have identified few variants that mediate their effect through insulin resistance. The aim of this study was to evaluate two quantitative, directly assessed measures of insulin resistance, namely insulin sensitivity index (S(I)) and insulin disposition index (DI), in Hispanic-American participants using an agnostic, high-density single nucleotide polymorphism (SNP) scan, and to validate these findings in additional samples.

METHODS

A two-stage GWAS was performed in Hispanic-American samples from the Insulin Resistance Atherosclerosis Family Study. In Stage 1, 317,000 SNPs were assessed using 229 DNA samples. SNPs with evidence of association with glucose homeostasis and adiposity traits were then genotyped on the entire set of Hispanic-American samples (n = 1,190). This report focuses on the glucose homeostasis traits: S(I) and DI.

RESULTS

Although evidence of association did not reach genome-wide significance (p = 5 x 10(-7)), in the combined analysis SNPs had admixture-adjusted p values of p (ADD) = 0.00010-0.0020 with 8 to 41% differences in genotypic means for S(I) and DI.

CONCLUSIONS/INTERPRETATION

Several candidate loci were identified that are nominally associated with S(I) and/or DI in Hispanic-American participants. Replication of these findings in independent cohorts and additional focused analysis of these loci is warranted.

Potential donor-recipient MYH9 genotype interactions in posttransplant nephrotic syndrome after pediatric kidney transplantation

Recurrence of focal segmental glomerulosclerosis (FSGS) with nephrotic syndrome is relatively common after kidney transplantation in young recipients whose predialysis course consists of heavy proteinuria, hypertension and subacute loss of kidney function. The gene(s) mediating this effect remain unknown. We report an unusual circumstance where kidneys recovered from a deceased African American male donor with MYH9-related occult FSGS (risk variants in seven of eight MYH9 E1 haplotype single nucleotide polymorphisms) were transplanted into an African American male child with risk variants in four MYH9 E1 risk variants and a European American female teenager with two MYH9 E1 risk variants. Fulminant nephrotic syndrome rapidly developed in the African American recipient, whereas the European American had an uneventful posttransplant course. The kidney donor lacked significant proteinuria at the time of organ procurement. This scenario suggests that donor-recipient interactions in MYH9, as well as other gene-gene and gene-environment interactions, may lead to recurrent nephrotic syndrome after renal transplantation. The impact of transplanting kidneys from donors with multiple MYH9 risk alleles into recipients with similar genetic background at high risk for recurrent kidney disease needs to be determined.

Association of 25-hydroxyvitamin D with blood pressure in predominantly 25-hydroxyvitamin D deficient Hispanic and African Americans

BACKGROUND

Several observational studies have recently suggested an inverse association of circulating levels of vitamin D with blood pressure. These findings have been based mainly on Caucasian populations; whether this association also exists among Hispanic and African Americans has yet to be definitively determined. This study investigates the association of 25-hydroxyvitamin D (25[OH]D) with blood pressure in Hispanic and African Americans.

METHODS

The data source for this study is the Insulin Resistance Atherosclerosis Family Study (IRASFS), which consists of Hispanic- and African-American families from three US recruitment centers (n =1,334). A variance components model was used to analyze the association of plasma 25[OH]D levels with blood pressure.

RESULTS

An inverse association was found between 25[OH]D and both systolic (beta for 10 ng/ml difference = -2.05; P < 0.01) and diastolic (beta for 10 ng/ml difference = -1.35; P < 0.001) blood pressure in all populations combined, after adjusting for age, sex, ethnicity, and season of blood draw. Further adjustment for body mass index (BMI) weakened this association (beta for 10 ng/ml difference = -0.94; P = 0.14 and beta for 10 ng/ml difference = -0.64; P = 0.09, respectively).

CONCLUSIONS

25[OH]D levels are significantly inversely associated with blood pressure in Hispanic and African Americans from the IRASFS. However, this association was not significant after adjustment for BMI. Further research is needed to determine the role of BMI in this association. Large, well-designed prospective studies of the effect of vitamin D supplementation on blood pressure may be warranted.

A genome-wide association scan for acute insulin response to glucose in Hispanic-Americans: the Insulin Resistance Atherosclerosis Family Study (IRAS FS)

AIMS/HYPOTHESIS

This study sought to identify genes and regions in the human genome that are associated with the acute insulin response to glucose (AIRg), an important predictor of type 2 diabetes, in Hispanic-American participants from the Insulin Resistance Atherosclerosis Family Study (IRAS FS).

METHODS

A two-stage genome-wide association scan (GWAS) was performed in IRAS FS Hispanic-American samples. In the first stage, 317K single nucleotide polymorphisms (SNPs) were assessed in 229 Hispanic-American DNA samples from 34 families from San Antonio, TX, USA. SNPs with the most significant associations with AIRg were genotyped in the entire set of IRAS FS Hispanic-American samples (n = 1,190). In chromosomal regions with evidence of association, additional SNPs were genotyped to capture variation in genes.

RESULTS

No individual SNP achieved genome-wide levels of significance (p < 5 x 10(-7)); however, two regions (chromosomes 6p21 and 20p11) had multiple highly ranked SNPs that were associated with AIRg. Additional genotyping in these regions supported the initial evidence of variants contributing to variation in AIRg. One region resides in a gene desert between PXT1 and KCTD20 on 6p21, while the region on 20p11 has several viable candidate genes (ENTPD6, PYGB, GINS1 and RP4-691N24.1).

CONCLUSIONS/INTERPRETATION

A GWAS in Hispanic-American samples identified several candidate genes and loci that may be associated with AIRg. These associations explain a small component of variation in AIRg. The genes identified are involved in phosphorylation and ion transport, and provide preliminary evidence that these processes are important in beta cell response.

Ethnic variation in the correlation between random serum glucose concentration and glycated haemoglobin

AIMS

To determine if the relationship between serum glucose concentration and glycated haemoglobin is different between African-Americans and whites.

METHODS

Retrospective cross-sectional study comparing the association between glycated haemoglobin and serum glucose levels, based upon ethnicity. Two databases were evaluated: (i) 4215 African-American and 6359 white outpatients who had simultaneous glycated haemoglobin, random serum glucose and creatinine concentration measurements between 2000 and 2007 at the North Carolina Baptist Hospital and (ii) 1021 white and 312 African-American Diabetes Heart Study (DHS) participants.

RESULTS

In North Carolina Baptist Hospital clinic attendees, a given glycated haemoglobin was associated with higher serum glucose concentrations in African-Americans compared with whites. In a multivariate model with glycated haemoglobin as the outcome variable, racial differences remained significant after adjustment for serum glucose, age, gender and kidney function. For individuals with a serum glucose between 5.6 and 8.3 mmol/l, the glucose : glycated haemoglobin ratio was 1.03 +/- 0.16 mmol/l/% in white individuals and 0.99 +/- 0.17 mmol/l/% in African-Americans (P < 0.0001). For a glycated haemoglobin value of 7.0%, there was a 0.98-mmol/l difference in predicted serum glucose concentration in 50-year-old African-American men, relative to white. Results were replicated in the DHS, where in a best-fit linear model, after adjustment for glucose, African-American race was a significant predictor of glycated haemoglobin (P < 0.0001).

CONCLUSIONS

African-Americans have higher glycated haemoglobin values at given serum glucose concentrations relative to whites. This finding may contribute to the observed difference in glycated haemoglobin values reported between these race groups.

Variants in intron 13 of the ELMO1 gene are associated with diabetic nephropathy in African Americans

Variants in the engulfment and cell motility 1 (ELMO1) gene are associated with nephropathy due to type 2 diabetes mellitus (T2DM) in a Japanese cohort. We comprehensively evaluated this gene in African American (AA) T2DM patients with end-stage renal disease (ESRD). Three hundred and nine HapMap tagging SNPs and 9 reportedly associated SNPs were genotyped in 577 AA T2DM-ESRD patients and 596 AA non-diabetic controls, plus 43 non-diabetic European American controls and 45 Yoruba Nigerian samples for admixture adjustment. Replication analyses were conducted in 558 AA with T2DM-ESRD and 564 controls without diabetes. Extension analyses included 328 AA with T2DM lacking nephropathy and 326 with non-diabetic ESRD. The original and replication analyses confirmed association with four SNPs in intron 13 (permutation p-values for combined analyses = 0.001-0.003), one in intron 1 (P = 0.004) and one in intron 5 (P = 0.002) with T2DM-associated ESRD. In a subsequent combined analysis of all 1,135 T2DM-ESRD cases and 1,160 controls, an additional 7 intron 13 SNPs produced evidence of association (P = 3.5 x 10(-5)- P = 0.05). No associations were seen with these SNPs in those with T2DM lacking nephropathy or with ESRD due to non-diabetic causes. Variants in intron 13 of the ELMO1 gene appear to confer risk for diabetic nephropathy in AA.

Heterogeneity in gene loci associated with type 2 diabetes on human chromosome 20q13.1

Human chromosome 20q12-q13.1 has been linked to type 2 diabetes mellitus (T2DM) in multiple studies. We screened a 5.795-Mb region for diabetes-related susceptibility genes in a Caucasian cohort of 310 controls and 300 cases with T2DM and end-stage renal disease (ESRD), testing 390 SNPs for association with T2DM-ESRD. The most significant SNPs were found in the perigenic regions: HNF4A (hepatocyte nuclear factor 4alpha), SLC12A5 (potassium-chloride cotransporter member 5), CDH22 (cadherin-like 22), ELMO2 (engulfment and cell motility 2), SLC13A3 (sodium-dependent dicarboxylate transporter member 3), and PREX1 (phosphatidylinositol 3,4,5-triphosphate-dependent RAC exchanger 1). Haplotype analysis found six haplotype blocks globally associated with disease (p<0.05). We replicated the PREX1 SNP association in an independent case-control T2DM population and inferred replication of CDH22, ELMO2, SLC13A3, SLC12A5, and PREX1 using in silico perigenic analysis of two T2DM Genome-Wide Association Study data sets. We found substantial heterogeneity between study results.

Genetic epidemiology of subclinical cardiovascular disease in the diabetes heart study

A genome-wide linkage scan of 357 European American (EA) and 72 African American (AA) pedigrees multiplex for type 2 diabetes mellitus (T2DM) was performed with multipoint nonparametric QTL linkage analysis. Four subclinical measures of cardiovascular disease (CVD): coronary artery (CCP), carotid artery (CarCP), and abdominal aortic calcified plaque (AACP) and carotid artery intima-media thickness (IMT) were mapped. Analyses were adjusted for age, gender, body mass index, and (if appropriate) ethnicity and diabetes status. Evidence for linkage was observed in EA T2DM subjects to CarCP near 16p13 (LOD=4.39 at 8.4 cM; P = 0.00001). When all EA subjects were included, the LOD score was 2.52, suggesting an amplification of the linkage by diabetes. Linkage analysis of a principal components measure of vascular calcium (LOD = 3.85 at 9.3 cM on 16p in EA T2DM subjects) and bivariate analysis of CarCP X IMT (LOD = 3.77 at 9.3 cM on 16p in EA T2DM subjects) were consistent with this linkage. In addition, evidence for linkage was observed with CCP near D15S1515 (LOD = 2.34) in EAs. Additional loci on chromosomes 1, 2, 7, 10, 13, and 21 had LODs > 2.0. The identification of trait-determining polymorphisms underlying these linkages will help delineate risk factors for CVD in T2DM and the general population.

Genome-wide linkage scans for renal function and albuminuria in Type 2 diabetes mellitus: the Diabetes Heart Study

AIMS/HYPOTHESIS

Glomerular filtration rate (GFR), end-stage renal disease and albuminuria are highly heritable. We performed a genome-wide linkage scan in 416 Diabetes Heart Study (DHS) families to detect loci that contributed to renal function and albuminuria.

MATERIALS AND METHODS

A total of 1067 individuals (900 with Type 2 diabetes mellitus) from 348 European American and 68 African American DHS families had measures of urine albumin : creatinine ratio (ACR), serum creatinine concentration and Modification of Diet in Renal Disease estimated GFR (eGFR). Variance components quantitative trait linkage analysis (using SOLAR) was computed.

RESULTS

Participants had mean +/- sd age 61.4 +/- 9.4 years; diabetes duration 10.5 +/- 7.4 years; eGFR 1.15 +/- 0.32 ml/sec; and urine ACR 15.8 +/- 67.2 mmol/l (median 1.4). In all families, significant evidence for linkage of GFR was observed on chromosome 2p16 (log of the odds; LOD = 4.31 at 72.0 cM, ATA47C04P/D2S1352) and 1p36 (LOD = 3.81 at 45.0 cM, D1S3669/D1S3720), with suggestive evidence on 7q21 (LOD = 2.42 at 99.0 cM, D7S820/D7S821) and 13q13 (LOD = 2.28 at 28.0 cM, D13S1493/D13S894). The evidence for linkage to ACR was far weaker, on 13q21-q22 (LOD = 1.84 at 50 cM, D13S1807/D13S800), 3p24-p23 (LOD = 1.81 at 58 cM, D3S3038/D3S2432) and 10p11 (LOD = 1.78 at 71.0 cM, D10S1208/D10S1221).

CONCLUSIONS/INTERPRETATIONS

The eGFR linkage peaks on 2p16, 7q21 and 13q13 closely overlap with nephropathy peaks identified in family studies enriched for severe kidney disease. These diabetes-enriched families provide an opportunity to map genes regulating renal function, potentially leading to the identification of genes producing nephropathy susceptibility in subjects with Type 2 diabetes.

Type 2 diabetes is not independently associated with spinal trabecular volumetric bone mineral density measured by QCT in the Diabetes Heart Study

The purpose of this study was to investigate the association between type 2 diabetes mellitus (DM2) and trabecular volumetric bone mineral density (vBMD) of the thoracic and lumbar spine measured by quantitative computed tomography (QCT) in 483 female (410 with DM2) and 398 male (365 with DM2) adults (age 36-86 years, BMI 16-58, 88% with DM2) in the Diabetes Heart Study. After accounting for familial correlation using generalized estimating equations (GEE), lumbar spine vBMD was positively associated with BMI (r = 0.24, P < 0.0001) and inversely associated with age (r = -0.51, P < 0.0001). In women, age-adjusted thoracic spinal vBMD (mg/ml, mean +/- SE) was higher in diabetics (147.6 +/- 2.3) compared to unaffected individuals (138.6 +/- 3.4) (P = 0.02), with age-adjusted lumbar spinal vBMD showing a similar but non-significant trend (132.9 +/- 2.1 in diabetics vs. 127.2 +/- 3.6 in unaffected individuals, P = 0.15). In contrast, in men, age-adjusted lumbar and thoracic vBMD were not different between diabetics and unaffected controls (lumbar vBMD = 125.0 +/- 1.8 in diabetics and 125.8 +/- 5.6 in unaffected individuals, P = 0.89; thoracic vBMD = 137.4 +/- 2.1 in diabetics vs. 134.2 +/- 5.5 in controls, P = 0.56). After multivariate analysis adjusting for age, sex, race, BMI, physical activity, dietary intake, smoking, and alcohol use, interaction between diabetes status and trabecular vBMD of the spine was no longer observed. In women only, age-adjusted areal BMD (determined by dual X-ray absorptiometry (DXA)) of the spine and hip were significantly higher in diabetics than non-diabetic (all P < 0.05), although the differences disappeared after additional adjustment for BMI. These data suggest that areal BMD measured by DXA and trabecular volumetric BMD measured by QCT are not associated with type 2 diabetes independently from BMI.

Association of genes of lipid metabolism with measures of subclinical cardiovascular disease in the Diabetes Heart Study

BACKGROUND

Dyslipidaemia is a well known risk factor for cardiovascular disease (CVD). Lipid metabolism is affected by a range of genes and proteins. This study investigated whether some of these genes are associated with measures of subclinical CVD.

METHODS

Polymorphisms of paraoxonase 1 and 2, cholesteryl ester transfer protein, hepatic lipase, and lipoprotein lipase were tested for associations with measures of subclinical CVD including carotid intima-media thickness measured by B-mode ultrasound and carotid and coronary arterial calcification measured by computed tomography. Analysis was performed in 620 European American participants in the Diabetes Heart Study, 83% of whom had type 2 diabetes mellitus. Associations of genotypes with subclinical CVD were tested by computing a series of generalised estimating equations.

RESULTS

The Q192R variant of paraoxonase 1 and rs285 of lipoprotein lipase were associated with carotid artery calcium (p values = 0.002 and 0.005, respectively). Paraoxonase 2 S311C was associated with coronary artery calcium (p value = 0.037).

CONCLUSIONS

There is evidence for modest, but significant, association of multiple single nucleotide polymorphisms in lipid genes with measures of subclinical CVD.

Hormone replacement therapy is associated with increased C-reactive protein in women with Type 2 diabetes in the Diabetes Heart Study

AIMS

Increased levels of inflammatory biomarkers, especially C-reactive protein (CRP), are associated with increased risk for cardiovascular disease (CVD) events, such as myocardial infarction, stroke, peripheral vascular disease, and sudden cardiac death. Medical interventions that increase CRP levels, such as hormone replacement therapy (HRT) in post-menopausal women, are under increasing scrutiny. The effect of HRT on CRP levels in women with Type 2 diabetes (T2DM) is not well documented, and conflicting conclusions have been reported. The aim of this study was to determine the influence of HRT on women with diabetes in a large cross-sectional study.

METHODS

Three hundred and twenty-seven post-menopausal women with T2DM from the Diabetes Heart Study participated. Current use of HRT was determined and serum CRP levels were measured using a high-sensitivity ELISA kit. Generalized estimating equation methods were used to assess the relationship of multiple clinical and lifestyle (e.g. smoking) measures on CRP levels including differences between women taking HRT (HRT+) and not taking HRT (HRT-).

RESULTS

Overall serum CRP levels were strongly associated with body mass index (P < 0.0001) and age (P < 0.0001). Of the women, 243 were not using HRT and 84 were using HRT. HRT+ and HRT- women did not differ significantly in measures of clinical traits, with the exception of higher mean low-density lipoprotein cholesterol in HRT- women (P = 0.004). In all models tested, HRT+ women had significantly higher circulating CRP levels, with P-values ranging from 0.0045 to 0.010.

CONCLUSIONS

In this study of serum CRP concentration as a function of HRT in women with Type 2 diabetes, there was consistent evidence for increased circulating CRP levels in women receiving oestrogen-containing HRT. Whether HRT-induced increases in CRP can account for the adverse cardiovascular effects of HRT remains to be established; however, based on these data, there is little reason to believe that diabetic women would be spared from such an effect.

Genetic mapping of a 17q chromosomal region linked to obesity phenotypes in the IRAS family study

OBJECTIVE

Obesity is widely accepted to be influenced by both environmental and genetic factors. Several recent studies have used the positional cloning approach in an attempt to discover genes contributing to obesity. In the IRAS Family Study a genomewide scan was performed on 1425 individuals of Hispanic descent (90 extended pedigree families) to identify regions of the genome linked to obesity phenotypes.

METHODS

Nonparametric QTL linkage analysis was performed using a variance components approach. The genome scan was performed in two phases: an initial genome scan in 45 families and a replication scan in 45 families. Fine mapping and candidate gene analyses were also performed. General estimating equations (GEE1) and quantitative pedigree disequilibrium tests (QPDT) were used for association analysis of single SNP and haplotype data.

RESULTS

Evidence for linkage to obesity traits was observed in each scan on the long arm of chromosome 17. When data from both scans was combined, a region on chromosome 17q was identified with evidence of linkage to visceral adipose tissue (VAT; LOD 3.11), waist circumference (WAIST) (LOD 2.5) and body mass index (BMI) (LOD 2.81). Nine additional microsatellite markers were identified and genotyped on all Hispanic individuals, with a mean marker density of approximately 1 marker/3 cM. Evidence of linkage remained significant with LOD 3.05 for VAT, LOD 2.44 for BMI and LOD 1.92 for WAIST. Fine mapping analyses suggest the possibility of two different obesity loci. In addition, the LOD - 1 interval of the major VAT peak decreased from 83-108 to 95-111 cM. Three positional candidate genes under the peak: somatostatin receptor 2 (SSTR2), galanin receptor 2 (GALR2), and growth hormone bound protein receptor 2 (GRB2) were chosen for detailed evaluation. Multiple polymorphisms within each candidate were genotyped and tested for association with the obesity phenotypes. Little evidence of association was detected between polymorphisms and obesity traits.

CONCLUSION

In conclusion, replication of linkage and fine mapping suggest that a region on chromosome 17q contains a gene (or genes) that contributes to the genetic etiology of obesity with the strongest evidence for linkage to VAT. Candidate genes in the region do not appear to account for the evidence of linkage. Additional studies are necessary to identify the obesity-related polymorphisms.

Association analysis of genes in the renin-angiotensin system with subclinical cardiovascular disease in families with Type 2 diabetes mellitus: the Diabetes Heart Study

AIMS

Cardiovascular disease (CVD) is a major complication of Type 2 diabetes mellitus. The renin-angiotensin system (RAS) and nitric oxide production are both important regulators of vascular function and blood pressure. Genes encoding proteins involved in these pathways are candidates for a contribution to CVD in diabetic patients. We have investigated variants of the angiotensinogen (AGT), angiotensin converting enzyme (ACE), angiotensin type 1 receptor (AT1R) and endothelial nitric oxide synthase (NOS3) genes for association with subclinical measures of CVD in families with Type 2 diabetes mellitus (T2DM).

METHODS

Atherosclerosis was measured by carotid intima-media thickness and calcification of the carotid and coronary arteries in 620 European Americans and 117 African Americans in the Diabetes Heart Study. Because of the role of these systems in blood pressure regulation, blood pressure was also investigated.

RESULTS

Compelling evidence of association was not detected with any of the SNPs with any outcome measures after adjustments for covariates despite sufficient power to detect relatively small differences in traits for specific genotype combinations.

CONCLUSIONS

Genetic variation of the RAS and NOS3 genes do not appear to strongly influence subclinical cardiovascular disease or blood pressure in this diabetic population.

Loci contributing to adult height and body mass index in African American families ascertained for type 2 diabetes

Height and body mass index (BMI) have high heritability in most studies. High BMI and reduced height are well-recognized as important risk factors for a number of cardiovascular diseases. We investigated these phenotypes in African American families originally ascertained for studies of linkage with type 2 diabetes using self-reported height and weight. We conducted a genome wide scan in 221 families containing 580 individuals and 672 relative pairs of African American descent. Estimates of heritability and support for linkage were assessed by genetic variance component analyses using SOLAR software. The estimated heritabilities for height and BMI were 0.43 and 0.64, respectively. We have identified major loci contributing to variation in height on chromosomes 15 (LOD = 2.61 at 35 cM, p = 0.0004), 3 (LOD = 1.82 at 84 cM, p = 0.0029), 8 (LOD = 1.92 at 135 cM, p = 0.0024) and 17 (LOD = 1.70 at 110 cM, p = 0.0044). A broad region on chromosome 4 supported evidence of linkage to variation in BMI, with the highest LOD = 2.66 at 168 cM (p = 0.0005). Two height loci and two BMI loci appear to confirm the existence of quantitative trait loci previously identified by other studies, providing important replicative data to allow further resolution of linkage regions suitable for positional cloning of these cardiovascular disease risk loci.

The impact of ethnicity and sex on subclinical cardiovascular disease: the Diabetes Heart Study

AIMS/HYPOTHESIS

African-Americans with type 2 diabetes and access to adequate healthcare are at lower risk of clinical coronary artery disease than are white diabetic patients. We evaluated whether ethnic differences in subclinical cardiovascular disease, coronary and carotid artery calcified plaque and carotid artery intima-medial thickness (IMT) were present in members of The Diabetes Heart Study families.

SUBJECTS AND METHODS

In a bi-racial cohort of 1,180 individuals from families enriched for members with type 2 diabetes, we calculated coronary and carotid artery calcified plaque using fast-gated helical computed tomography, and measured carotid artery IMT and clinical risk factor profiles. Generalised estimating equations were used to test for an association between measures of subclinical cardiovascular disease and ethnicity and sex.

RESULTS

After adjustment for age, ethnicity and kidney function, African-Americans had significantly lower amounts of coronary artery calcified plaque (mean+/-SE) (866+/-158 vs 1,915+/-135, respectively; p=0.0466) and carotid artery calcified plaque (179+/-51 vs 355+/-27, respectively; p=0.0240) relative to whites, despite having increased carotid IMT (0.71+/-0.01 vs 0.67+/-0.004 cm, respectively; p=0.0007), and higher blood pressure, albuminuria and HbA1c. Sex-specific analyses revealed that African-American men had significantly lower coronary and carotid artery calcified atheroma than white men. In women, ethnic differences in calcified carotid artery plaque, but not coronary artery plaque, were observed.

CONCLUSIONS/INTERPRETATION

In families enriched for members with type 2 diabetes, African-American men had markedly lower levels of coronary and carotid artery calcified plaque than white men, despite increased carotid artery IMT and conventional risk factors. These findings suggest that susceptibility to subclinical cardiovascular disease differs markedly according to ethnicity and sex.

Quantitative trait loci for abdominal fat and BMI in Hispanic-Americans and African-Americans: the IRAS Family study

OBJECTIVE

To conduct linkage analysis for body mass index (BMI, kg/m2), waist-to-hip ratio (WHR), visceral adipose tissue mass (VAT, cm2) and subcutaneous adipose tissue mass (SAT, cm2) using a whole genome scan.

DESIGN

Cross-sectional family study.

STUDY SUBJECTS

African-American families from Los Angeles (AA, n=21 extended pedigrees) and Hispanic-American families (HA) from San Antonio, TX (HA-SA, n=33 extended pedigrees) and San Luis Valley, CO (HA-SLV, n=12 extended pedigrees), totaling 1049 individuals in the Insulin Resistance and Atherosclerosis (IRAS) Family Study.

MEASUREMENTS

VAT and SAT were measured using a computed tomography scan obtained at the fourth and fifth lumbar vertebrae. All phenotypes were adjusted for age, gender, and study center. VAT, SAT, and WHR were analyzed both unadjusted and adjusted for BMI.

RESULTS

Significant linkage to BMI was found at D3S2387 (LOD=3.67) in African-Americans, and at D17S1290 in Hispanic-Americans (LOD=2.76). BMI-adjusted WHR was linked to 12q13-21 (D12S297 (LOD=2.67) and D12S1052 (LOD=2.60)) in Hispanic-Americans. The peak LOD score for BMI-adjusted VAT was found at D11S2006 (2.36) in Hispanic families from San Antonio. BMI-adjusted SAT was linked to D5S820 in Hispanic families (LOD=2.64). Evidence supporting linkage of WHR at D11S2006, VAT at D17S1290, and SAT at D1S1609, D3S2387, and D6S1056 was dependent on BMI, such that the LOD scores became nonsignificant after adjustment of these phenotypes for BMI.

CONCLUSIONS

Our findings both replicate previous linkage regions and suggest novel regions in the genome that may harbor quantitative trait locis contributing to variation in measures of adiposity.

Association of adipose tissue deposition and beta-2 adrenergic receptor variants: the IRAS family study

OBJECTIVE

Adipose tissue distribution (visceral vs subcutaneous) has been shown to be an important predictor of insulin resistance, diabetes and cardiovascular disease, independent of body mass index. The beta-2 adrenergic receptor is a major lipolytic receptor in human fat cells and the gene that codes for this protein is an important candidate gene for measures of adiposity and fat deposition. We examined whether two common polymorphisms in codons 16 (Arg16Gly) and 27 (Gln27Glu) are associated with measures of fat distribution in participants of the IRAS Family Study.

METHODS

We recruited African-American (AA) and Hispanic-American (HA) families from Los Angeles, CA, USA (18 pedigrees, 272 AA individuals), San Antonio, TX, USA (33 pedigrees, 448 HA individuals) and San Luis Valley, CO, USA (12 pedigrees, 272 HA individuals). We estimated adipose tissue distribution via computed tomography. To test for an association between adiposity measures and these polymorphisms, we used generalized estimating equations, adjusting for age, gender, clinical site (ethnicity), body mass index, and familial correlation.

RESULTS

Of the 992 individuals genotyped for these polymorphisms, 57% were female and 15% had been diagnosed with type 2 diabetes mellitus. The mean age was 42.7+/-14.6 y. The Glu27 allele of the Gln27Glu polymorphism was positively associated with (P-value for recessive model): body mass index (0.025), visceral adipose tissue (<0.0001) and visceral-to-subcutaneous adipose ratio (0.009), but not with subcutaneous adipose tissue (0.952). The Arg16Gly polymorphism was not associated with any of the adiposity measures.

CONCLUSIONS

These findings suggest that genetic variation in the beta-2 adrenergic receptor gene influences fat deposition and body size in AAs and HAs. In particular, these results support a role for the gene in the distribution of visceral adipose tissue but not subcutaneous adipose tissue.

Heritability of spinal trabecular volumetric bone mineral density measured by QCT in the Diabetes Heart Study

The heritability of trabecular volumetric bone mineral density (BMD) determined by quantitative computed tomography (QCT) has not yet been reported. The purpose of this study was to investigate the heritability of BMD as determined by QCT and DXA in 124 women and 120 men (age 39-83 years, BMI 17-75, 84% type 2 diabetics) from 101 families (232 sibling pairs) in the Diabetes Heart Study. Volumetric BMD had a heritability (h2) estimate of 0.73 (SE = 0.15, P < 0.0001) at the lumbar spine and 0.71 (SE = 0.15, P < 0.0001) at the thoracic spine. Areal BMD heritability estimates were 0.56 for PA spine, 0.43 for total hip, 0.43 for femoral neck, 0.45 for distal radius, 0.42 for mid-radius, and 0.52 for whole body (all P < 0.01). After accounting for familial correlation using generalized estimating equations, volumetric BMD was inversely associated with age (r = -0.52, P < 0.0001) and duration of diabetes (r = -0.24, P < 0.01) and positively associated with body weight (r = 0.25, P < 0.01). In multivariate analysis, adjustment for age, sex, and race lowered the h2 estimates for volumetric BMD at the lumbar (h2 = 0.41, P < 0.01) and thoracic (h2 = 0.48, P < 0.001) spine, increased the h2 estimate for areal BMD at the mid radius (h2 = 0.58, P < 0.0001), and had little effect on the h2 estimate for areal BMD at other sites (h2 = 0.41-0.55, all P < 0.01). Additional adjustment for BMI, duration of diabetes, and physical activity had little effect on the h2 estimates for volumetric BMD or areal BMD except at the hip where they were lowered (h2 = 0.31-0.33, all P < 0.05). These data suggest that, like areal BMD, volumetric BMD is highly heritable and may be used in designing linkage studies to locate genes governing bone metabolism.

Adiponectin as a novel determinant of bone mineral density and visceral fat

Growing evidence suggests that positive associations between fat mass (FM) and bone mineral density (BMD) are mediated by not only biomechanical but also biochemical factors. Adiponectin is a novel adipocyte-derived hormone that regulates energy homeostasis and has anti-inflammatory and anti-atherogenic effects. Unlike other adipokines such as leptin, adiponectin levels decrease in obesity and type 2 diabetes. The purpose of our study was to investigate associations of serum adiponectin with BMD (DXA and QCT), FM (DXA and QCT), and serum leptin and soluble leptin receptor levels in 38 women and 42 men (age 39-81, BMI 17-55, 86% with type 2 diabetes). After adjusting for age, gender, race, smoking, and diabetes status, serum adiponectin was inversely associated with areal BMD (r = -0.20 to -0.3, all P < 0.01), volumetric BMD (r = -0.35 to -0.44, all P < 0.01), and visceral fat volume (r = -0.30, P < 0.01). These associations remained significant after adjusting for whole body fat mass. The associations of adiponectin with subcutaneous fat volume, whole body FM, and serum leptin level were not significant (all P > 0.1). These data suggest that adiponectin may play a role in the protective effects of visceral fat on BMD.

Identification of a novel human cytokine gene in the interleukin gene cluster on chromosome 2q12-14

Genes in the interleukin-1 (IL-1) gene cluster on human chromosome 2 play an important role in mediating inflammatory responses and are associated with numerous diseases. We have identified a novel IL-1-like gene, IL-1F10, on human chromosome 2q13-14.1 near the IL-1 receptor antagonist gene (IL-1RN). The IL1F10 gene is encoded by 5 exons spanning over 7.8 kb of genomic DNA. The 1008-bp IL-1F10 cDNA encodes a 152-amino acid protein that shares between 41% and 43% amino acid identity with human IL-1 receptor antagonist (IL-1Ra) and FIL-1delta, respectively. IL-1F10 shares characteristics of the IL-1Ra family, including key amino acid consensus sequences and a similar genomic structure. By multitissue first-strand cDNA PCR analysis, IL-1F10 mRNA is expressed in heart, placenta, fetal liver, spleen, thymus, and tonsil. The expression in a variety of immune tissues and similarity to IL-1Ra suggest a role of IL-1F10 in the inflammatory response.

Sequence and functional analysis of GLUT10: a glucose transporter in the Type 2 diabetes-linked region of chromosome 20q12-13.1

We have carried out a detailed sequence and functional analysis of a novel human facilitative glucose transporter, designated GLUT10, located in the Type 2 diabetes-linked region of human chromosome 20q12-13.1. The GLUT10 gene is located between D20S888 and D20S891 and is encoded by 5 exons spanning 26.8 kb of genomic DNA. The human GLUT10 cDNA encodes a 541 amino acid protein that shares between 31 and 35% amino acid identity with human GLUT1-8. The predicted amino acid sequence of GLUT10 is nearly identical in length to the recently described GLUT9 homologue, but is longer than other known members of the GLUT family. In addition, we have cloned the mouse cDNA homolog of GLUT10 that encodes a 537 amino acid protein that shares 77.3% identity with human GLUT10. The amino acid sequence probably has 12 predicted transmembrane domains and shares characteristics of other mammalian glucose transporters. Human and mouse GLUT10 retain several sequence motifs characteristic of mammalian glucose transporters including VP497ETKG in the cytoplasmic C-terminus, G73R[K,R] between TMD2 and TMD3 (PROSITE PS00216), VD92RAGRR between TMD8 and TMD9 (PROSITE PS00216), Q242QLTG in TMD7, and tryptophan residues W430 (TMD10) and W454 (TMD11), that correspond to trytophan residues previously implicated in GLUT1 cytochalasin B binding and hexose transport. Neither human nor mouse GLUT10 retains the full P[E,D,N]SPR motif after Loop6 but instead is replaced with P186AG[T,A]. A PROSITE search also shows that GLUT10 has lost the SUGAR TRANSPORT 2 pattern (PS00217), a result of the substitution G113S in TMD4, while all other known human GLUTs retain the glycine and the pattern match. The significance of this substitution is unknown. Sites for N-linked glycosylation are predicted at N334ATG between TMD8 and TMD9 and N526STG in the cytoplasmic C-terminus. Northern hybridization analysis identified a single 4.4-kb transcript for GLUT10 in human heart, lung, brain, liver, skeletal muscle, pancreas, placenta, and kidney. By RT-PCR analysis, GLUT10 mRNA was also detected in fetal brain and liver. When expressed in Xenopus oocytes, human GLUT10 exhibited 2-deoxy-D-glucose transport with an apparent Km of approximately 0.3 mM. D-Glucose and D-galactose competed with 2-deoxy-D-glucose and transport was inhibited by phloretin. The gene localization and functional properties suggest a role for GLUT10 in glucose metabolism and Type 2 diabetes.

A high-resolution 6.0-megabase transcript map of the type 2 diabetes susceptibility region on human chromosome 20

Recent linkage studies and association analyses indicate the presence of at least one type 2 diabetes susceptibility gene in human chromosome region 20q12-q13.1. We have constructed a high-resolution 6.0-megabase (Mb) transcript map of this interval using two parallel, complementary strategies to construct the map. We assembled a series of bacterial artificial chromosome (BAC) contigs from 56 overlapping BAC clones, using STS/marker screening of 42 genes, 43 ESTs, 38 STSs, 22 polymorphic, and 3 BAC end sequence markers. We performed map assembly with GraphMap, a software program that uses a greedy path searching algorithm, supplemented with local heuristics. We anchored the resulting BAC contigs and oriented them within a yeast artificial chromosome (YAC) scaffold by observing the retention patterns of shared markers in a panel of 21 YAC clones. Concurrently, we assembled a sequence-based map from genomic sequence data released by the Human Genome Project, using a seed-and-walk approach. The map currently provides near-continuous coverage between SGC32867 and WI-17676 ( approximately 6.0 Mb). EST database searches and genomic sequence alignments of ESTs, mRNAs, and UniGene clusters enabled the annotation of the sequence interval with experimentally confirmed and putative transcripts. We have begun to systematically evaluate candidate genes and novel ESTs within the transcript map framework. So far, however, we have found no statistically significant evidence of functional allelic variants associated with type 2 diabetes. The combination of the BAC transcript map, YAC-to-BAC scaffold, and reference Human Genome Project sequence provides a powerful integrated resource for future genomic analysis of this region.

Familial aggregation of coronary artery calcium in families with type 2 diabetes

Type 2 diabetes is widely recognized as a major risk factor for atherosclerotic cardiovascular disease, including subclinical atherosclerosis as measured by noninvasive procedures. However, the role of genetic factors that contribute to various measures of subclinical atherosclerosis is largely unknown. We hypothesize that subclinical atherosclerosis, measured as coronary artery calcification (CAC), will be extensive in individuals with type 2 diabetes and that its presence depends on both genetic and environmental factors. The genetic factors should result in the familial aggregation of CAC. To determine the extent of familial aggregation of CAC in the presence of type 2 diabetes, we studied 122 individuals with type 2 diabetes (mean age 60 years) and 13 individuals without diabetes in 56 families. CAC was measured by fast-gated helical computed tomography. Other measured factors included blood pressure, body size, lipids, HbA1c, and self-reported medical history. To test for an association between CAC and these factors while accounting for the potential familial correlation of CAC, generalized estimating equations were used. CAC was detectable in 80% of individuals with diabetes (median score 84, range 0-5,776). Extent of CAC, adjusted for age, was positively associated with male sex (P = 0.0003), reduced HDL (P = 0.02), albumin-to-creatinine ratio (P = 0.008), and cigarette pack-years (P = 0.03). CAC was also positively associated with a history of angina, myocardial infarction, stroke, and vascular procedures (all P < 0.01). HbA1c and fasting glucose were positively, but nonsignificantly, associated with the extent of CAC (P = 0.14 and 0.08, respectively). CAC, adjusted for age, sex, race, and diabetes status, was heritable (h2 = 0.50; P = 0.009). In multivariate analysis with additional adjustment for HDL, BMI, hypertension, and smoking, h2 = 0.40 (P = 0.038). These results suggest that strong (independent) genetic factors as well as environmental factors contribute to the variance of CAC in individuals with type 2 diabetes. In these data, CAC seems heritable and may serve as an important feature in designing studies to map genes contributing to both atherosclerosis and type 2 diabetes.

Genetic analysis of nitric oxide and endothelin in end-stage renal disease

BACKGROUND

Genetic factors have been implicated in the development of the common aetiologies of end-stage renal disease (ESRD), including renal failure attributed to hypertension, diabetes mellitus, systemic lupus erythematosus and human immunodeficiency virus infection. Nitric oxide (NO) and endothelin are powerful vasoactive mediators involved in inflammation and regulation of vascular tone and blood pressure. We evaluated the role of the neuronal constitutive (NOS1) and endothelial constitutive (NOS3) nitric oxide synthase genes and the endothelin-1 (EDN-1) gene in predisposition to chronic renal failure in African-Americans.

METHODS

The study population for the linkage and association analyses in ESRD consisted of 361 individuals from 168 multiplex African-American families. These individuals comprised 207 unweighted sibling pairs concordant for all-cause ESRD. Microsatellite markers NOS1B (NOS1), D7S636 (NOS3) and CPHD1-1/2 (EDN-1) were genotyped in the sample. In addition, a mutation, Glu298Asp, in exon 7 of NOS3 and a 27 bp variable number tandem repeat (VNTR) marker in intron 4 of NOS3 were evaluated in the sibling pairs and in an additional 92 unrelated African-Americans with type 2 diabetes mellitus-associated ESRD (singletons). Association analyses utilized the relative predispositional effect method. Model independent linkage analyses were performed using GeneHunter-plus and MapMaker/SIBS (exclusion analysis) software.

RESULTS

Significant evidence for association with ESRD was detected for alleles 7 and 9 of the NOS1 gene (11.9 and 34.2%, respectively, in unrelated probands of ESRD families versus 6.5 and 27.5%, respectively, in race-matched controls, both P:<0.01). These associations were maintained when the unrelated first sibling from each family was used in a case-control comparison and was most pronounced in the non-diabetic ESRD cases. The NOS3 and EDN-1 markers failed to provide consistent evidence for association in the sibling pairs and the diabetic ESRD singletons, although we identified two novel endothelial constitutive NOS4 (ecNOS4) VNTR alleles in African-Americans. Significant evidence for linkage was not detected between the NOS genes or the EDN-1 gene in either all-cause ESRD or when the ESRD sibling pairs were stratified by aetiology (type 2 diabetic ESRD or non-diabetic aetiologies).

CONCLUSION

Based upon the consistent allelic associations, we believe that further evaluation of the NOS1 gene in ESRD susceptibility in African-Americans is warranted.

Genomic structure of the human plasma prekallikrein gene, identification of allelic variants, and analysis in end-stage renal disease

Kallikreins are serine proteases that catalyze the release of kinins and other vasoactive peptides. Previously, we have studied one tissue-specific (H. Yu et al., 1996, J. Am. Soc. Nephrol. 7: 2559-2564) and one plasma-specific (H. Yu et al., 1998, Hypertension 31: 906-911) human kallikrein gene in end-stage renal disease (ESRD). Short sequence repeat polymorphisms for the human plasma kallikrein gene (KLKB1; previously known as KLK3) on chromosome 4 were associated with ESRD in an African American study population. This study of KLKB1 in ESRD has been extended by determining the genomic structure of KLKB1 and searching for allelic variants that may be associated with ESRD. Exon-spanning PCR primer sets were identified by serial testing of primer pairs designed from KLKB1 cDNA sequence and DNA sequencing of PCR products. Like the rat plasma kallikrein gene and the closely related human factor XI gene, the human KLKB1 gene contains 15 exons and 14 introns. The longest intron, F, is almost 12 kb long. The total length of the gene is approximately 30 kb. Sequence of the 5'-proximal promoter region of KLKB1 was obtained by shotgun cloning of genomic fragments from a bacterial artificial clone containing the KLKB1 gene, followed by screening of the clones using exon 1-specific probes. Primers flanking the exons and 5'-proximal promoter region were used to screen for allelic variants in the genomic DNA from ESRD patients and controls using the single-strand conformation polymorphism technique. We identified 12 allelic variants in the 5'-proximal promoter and 7 exons. Of note were a common polymorphism (30% of the population) at position 521 of KLKB1 cDNA, which leads to the replacement of asparagine with a serine at position 124 in the heavy chain of the A2 domain of the protein. In addition, an A716C polymorphism in exon 7 resulting in the amino acid change H189P in the A3 domain of the heavy chain was observed in 5 patients belonging to 3 ESRD families. A third polymorphism in the coding sequence was a C699A shift that caused an amino acid change, H183Q. This allele was observed in 8 cases from 6 ESRD families but was not found in any control DNAs. Individually or combined, the allelic variants observed are not statistically associated with ESRD, though in several cases (e.g., H183Q) the small number of people in the population carrying these alleles limits our ability to statistically test for significant association with ESRD. Two new CA/GT repeat polymorphic markers, designated KLK3f and KLK3g, that have heterozygosities of 0.65 and 0.84, respectively, were identified within introns M and N. Analysis using the relative predispositional effect technique indicated that the frequencies of alleles 4 and 8 of KLK3f and allele 8 of KLK3g were significantly different between controls and ESRD cases. They accounted for 0.226, 0.096, and 0.313, respectively, in the probands of 166 ESRD families compared to 0.172, 0.066, and 0.244 in 139 healthy race-matched controls (allele P and total P < 0.05 for all three alleles). Therefore, although polymorphisms in the coding and 5'-proximal promoter of KLKB1 show no statistically significant association with ESRD in African Americans, there is still evidence for association of this part of chromosome 4 with ESRD. This observation suggests that other sequences within or near KLKB1, or another gene nearby, may contribute to ESRD susceptibility.

Association of autoimmune thyroid disease with microsatellite markers for the thyrotropin receptor gene and CTLA-4 in Japanese patients

In a previous study we identified a microsatellite marker near the thyrotropin receptor (TSHR) gene. Studies with this marker, TSHR-CA, revealed a significant association between autoimmune thyroid disease (AITD) in Japanese patients and one specific allele (allele 1; 180 base pair [bp]) of the microsatellite sequence. In addition, weak evidence for association of AITD with two alleles of the CTLA-4 gene was observed. In the present study, TSHR-CA has been mapped to approximately 600 kb of the TSHR gene using radiation hybrid mapping. TSHR-CA and another TSHR microsatellite marker, TSHR-AT, which is located in intron 2 of TSHR gene, were genotyped in a set of 349 unrelated Japanese AITD patients and 218 Japanese controls. The TSHR-AT marker showed association in this Japanese AITD population with a significant increase in allele 5 (294 bp; p < 0.05) and a significant decrease in allele 7 (298 bp; p < 0.05). The association of allele 5 of TSHR-AT was also significant in hypothyroid patients (thyrotropin-binding inhibitory immunoglobulin-positive [TBII+], P < 0.01; thyrotropin-binding inhibitory immunoglobulin-negative [TBII-], p < 0.05). The association of allele 7 of TSHR-AT were also significant for the hypothyroid TBII+ patients (p < 0.05). The CTLA-4 gene was also genotyped in this expanded set of Japanese AITD patients and controls. Association between AITD susceptibility and allele 2 (102 bp; p < 0.01) and allele 4 (106 bp; p < 0.01) were observed. These associations were also observed with GD patients (allele 2, p < 0.01; allele 4, p < 0.01). Associations with TSHR-CA were observed for Hashimoto's thyroiditis (HT) patients with respect to alleles 3 (179 bp; p < 0.05) and 5 (175 bp; p < 0.05) and with hypothyroid TBII- patients for allele 4 (177 bp; p < 0.05). The presence of specific alleles of TSHR-CA, TSHR-AT, and CTLA-4 contribute significant increase in risk of development of AITD. These results confirm and expand on our previous study suggesting that alleles of the TSHR and CTLA-4 genes, or genes near them contribute to AITD susceptibility and set the stage for future studies of interactions between these genes and AITD.

Identification and characterization of PRKCBP1, a candidate RACK-like protein

The receptors for activated C-kinase (RACK) family of proteins function as anchors for activated protein kinase C (PKC) isoenzymes. Using a monoclonal antibody to RACK1 in the screening of a human hippocampus cDNA library, we identified a novel member of the RACK family, designated PRKCBP1. Immunoprecipitation assays performed with a GST-fused PRKCBP1 protein suggest the carboxy terminus of PRKCBP1 interacts specifically with PKCbetaI. Northern analysis detected a 3.1-kb PRKCBP1 transcript in all tissues examined including brain, heart, liver, lung, pancreas, skeletal muscle, kidney, and spleen. The PRKCBP1 gene has been localized to human Chromosome (Chr) 20q12-13.1. Several groups have reported evidence for genetic linkage of Type II diabetes to this region in Caucasian families. This localization, combined with the observation that abnormalities in the activation, translocation, and inhibition of PKC occur in the development of Type II diabetes, suggested that PRKCBP1 was a candidate for contributing to Type II diabetes. We determined the PRKCBP1 coding sequence is 1845 bp in length, dispersed over 9 exons, spanning approximately 34 kb of genomic DNA. SSCP analysis was used to screen PRKCBP1 coding regions for mutations or polymorphisms in 100 Caucasian Type II diabetics and 100 Caucasian unaffected individuals. A silent C/T transition (bp1413, Thr137) was present in 23% of both diabetic and control individuals. A C/T transition (bp198) was also identified in a single diabetic individual, which resulted in no coding change (Ser66). The results of this analysis suggest that PRKCBP1 coding variations are uncommon and do not contribute to Type II diabetes in the general population.

Analysis of the HNF4 alpha gene in Caucasian type II diabetic nephropathic patients

AIMS/HYPOTHESIS

Linkage and association studies in Caucasian patients with Type II (non-insulin-dependent) diabetes mellitus suggest that one or more diabetes susceptibility gene(s) reside within human chromosome 20q12-13.1. This region of chromosome 20 contains the maturity-onset diabetes of the young type 1 gene, HNF4 alpha. The purpose of this study was to assess the possible involvement of HNF4 alpha in Type II diabetes.

METHODS

Mutation analysis was done on the 12 exons and promoter regions of the HNF4 alpha gene in 182 Caucasian diabetic nephropathic patients and 100 Caucasian control subjects. The functional consequences of a novel promoter mutation were examined using a reporter system in the HepG2 liver cell line and electrophoretic mobility shift assays.

RESULTS

We identified two novel mutations in the HNF4 alpha, an R323H missense mutation in exon 8, and a 7 bp deletion (delta 7) in the proximal promoter region resulting in deletion of a single putative Sp1 binding site. Using a reporter assay system, the delta 7 sequence was found to exhibit a 51.2% (standard error +/- 4.2%) reduction in promoter activity relative to the normal sequence. In electrophoretic mobility shift assays using specific and non-specific competitors, the delta 7 sequence had a 45.5% (range 40.4-46.6) reduction in binding compared with the normal sequence. The delta 7 allele occurs in a family with multiple cases of Type II diabetes in a pattern consistent with coinheritance of the delta 7 allele and diabetes.

CONCLUSION/INTERPRETATION

Analysis of the HNF4 alpha gene revealed two possible mutations in 182 diabetic patients which suggests that the HNF4 alpha gene does not make a large contribution to diabetes susceptibility in the general population of Caucasian diabetic nephropathic patients. Functional analysis of the delta 7 promoter deletion suggests, however, that promoter mutations in otherwise normal genes could contribute to diabetes susceptibility.

Human Na+/H+ exchanger genes : identification of polymorphisms by radiation hybrid mapping and analysis of linkage in end-stage renal disease

The Na+/H+ exchangers (NHEs) are membrane-bound transporters that catalyze the electro-neutral movement of extracellular Na+ for intracellular H+. NHE genes play a critical role in pH homeostasis and cellular volume regulation and can be considered candidate genes for essential hypertension and renal disease. This study was performed to determine whether the NHE genes contributed to genetic susceptibility in end-stage renal disease (ESRD). To date, 5 isoforms of NHE have been cloned in mammals (NHE1 to NHE5). The complementary DNA (cDNA) sequences of NHE1 to NHE3 and NHE5 are known in humans. Because the chromosomal structure of the NHE genes is unknown, we used cDNA sequences to design polymerase chain reaction primers for use in radiation hybrid mapping. Radiation hybrid mapping of NHE genes identified nearby polymorphic markers for NHE1 to NHE3 (NHE1: D1S197, D1S2677; NHE2: D2S373, D2S1789; and NHE3: D5S678, D5S2005). We used these markers, and other previously identified polymorphic markers for NHE5, in linkage and association analyses of ESRD. The NHE1 to NHE3 and NHE5 loci did not demonstrate evidence for linkage to ESRD. However, NHE5 showed significant evidence for association (P</=1.0x10(-4)). The strongest evidence for association was observed with allele 6 of NHE5 (P</=0.001 to 0. 01). Allele 6 appeared to have a renoprotective effect, with a frequency of 0.15 in the control population and 0.06 to 0.09 in patients with ESRD. The combined approach of designing primers from cDNA and radiation hybrid mapping has proven successful in identifying polymorphisms for human genes of which only cDNA sequences were previously available. The NHE primers and associated polymorphic loci identified in this study can be used in genomic, linkage, and association analysis of NHE genes in future genetic studies of hypertension and renal failure. Given the allelic association, further evaluation of the role of NHE5 in ESRD susceptibility appears warranted.

Mutations of the cathepsin C gene are responsible for Papillon-Lefèvre syndrome

Papillon-Lefèvre syndrome (PLS) is an autosomal recessive disorder characterised by palmoplantar hyperkeratosis and severe early onset periodontitis that results in the premature loss of the primary and secondary dentitions. A major gene locus for PLS has been mapped to a 2.8 cM interval on chromosome 11q14. Correlation of physical and genetic maps of this interval indicate it includes at least 40 ESTs and six known genes including the lysosomal protease cathepsin C gene (CTSC). The CTSC message is expressed at high levels in a variety of immune cells including polymorphonuclear leucocytes, macrophages, and their precursors. By RT-PCR, we found CTSC is also expressed in epithelial regions commonly affected by PLS, including the palms, soles, knees, and oral keratinised gingiva. The 4.7 kb CTSC gene consists of two exons. Sequence analysis of CTSC from subjects affected with PLS from five consanguineous Turkish families identified four different mutations. An exon 1 nonsense mutation (856C-->T) introduces a premature stop codon at amino acid 286. Three exon 2 mutations were identified, including a single nucleotide deletion (2692delA) of codon 349 introducing a frameshift and premature termination codon, a 2 bp deletion (2673-2674delCT) that results in introduction of a stop codon at amino acid 343, and a G-->A substitution in codon 429 (2931G-->A) introducing a premature termination codon. All PLS patients were homozygous for cathepsin C mutations inherited from a common ancestor. Parents and sibs heterozygous for cathepsin C mutations do not show either the palmoplantar hyperkeratosis or severe early onset periodontitis characteristic of PLS. A more complete understanding of the functional physiology of cathepsin C carries significant implications for understanding normal and abnormal skin development and periodontal disease susceptibility.

A physical map of the 20q12-q13.1 region associated with type 2 diabetes

Several recent genetic studies have suggested linkage of Type 2 diabetes (non-insulin-dependent diabetes mellitus) susceptibility to a region of chromosome 20q12-q13.1. To facilitate the identification and cloning of a diabetes susceptibility gene(s) in this region, we have constructed correlated radiation hybrid and YAC/BAC contig physical maps of the region. A high-resolution radiation hybrid map encompassing 9.5 Mb between the PLC and the CEBPB genes was constructed using 68 markers: 25 polymorphic markers, 15 known genes, 21 ESTs, and 7 random genomic sequences. The physical order of the polymorphic markers within this radiation hybrid map is consistent with published genetic maps. A YAC/BAC contig that gives continuous coverage between PLC and CEBPB was also constructed. This contig was constructed from 24 YACs, 34 BACs, and 1 P1 phage clone onto which 71 markers were mapped: 23 polymorphic markers, 12 genes, 24 ESTs, and 12 random genomic sequences. The radiation hybrid map and YAC/BAC physical map enable precise mapping of newly identified transcribed sequences and polymorphic markers that will aid in linkage and linkage disequilibrium studies and facilitate identification and cloning of candidate Type 2 diabetes susceptibility genes residing in 20q12-q13.1.

Race-specific HIV-1 disease-modifying effects associated with CCR5 haplotypes

Genetic variation in CC chemokine receptor 5 (CCR5), the major HIV-1 coreceptor, has been shown to influence HIV-1 transmission and disease progression. However, it is generally assumed that the same CCR5 genotype (or haplotype) has similar phenotypic effects in different populations. To test this assumption, we used an evolutionary-based classification of CCR5 haplotypes to determine their associated HIV-1 disease-modifying effects in a large well-characterized racially mixed cohort of HIV-1-seropositive individuals. We demonstrate that the spectrum of CCR5 haplotypes associated with disease acceleration or retardation differs between African Americans and Caucasians. Also, we show that there is a strong interactive effect between CCR5 haplotypes with different evolutionary histories. The striking population-specific phenotypic effects associated with CCR5 haplotypes emphasize the importance of understanding the evolutionary context in which disease susceptibility genes are expressed.

Evaluation of markers on human chromosome 10, including the homologue of the rodent Rf-1 gene, for linkage to ESRD in black patients

There is abundant evidence supporting the contribution of genetic factors to the development of end-stage renal disease (ESRD) in blacks. Two renal failure susceptibility genes, Rf-1 and Rf-2, have been identified in the fawn-hooded rat, an animal model of hypertension and nephrosclerosis. The human homologous region containing the rodent Rf-1 gene has been localized to chromosome 10q. We tested for genetic linkage between 21 polymorphic markers on human chromosome 10 and chronic renal failure in 129 black sibling pairs concordant for ESRD. Two adjacent markers on 10p, D10S1435 and D10S249 (4 centiMorgans from D10S1435), approached significance for linkage to ESRD in sibling pairs with nondiabetic causes of ESRD (P = 0.035 pairwise, P = 0.082 multipoint for D10S1435; P = 0.074 pairwise, P = 0.063 multipoint for D10S249). The markers spanning the homologous region of Rf-1 did not show evidence for linkage to ESRD in sibling pairs concordant for diabetic ESRD, sibling pairs concordant for nondiabetic causes of ESRD, or in the entire family set. These results suggest that the human homologue of Rf-1 is unlikely to contribute substantially to renal failure susceptibility from the common causes of kidney disease in blacks.

A common DLX3 gene mutation is responsible for tricho-dento-osseous syndrome in Virginia and North Carolina families

Tricho-dento-osseous syndrome (TDO) is characterised by a variable clinical phenotype primarily affecting the hair, teeth, and bone. Different clinical features are observed between and within TDO families. It is not known whether the variable clinical features are the result of genetic heterogeneity or clinical variability. A gene for TDO was localised recently to chromosome 17q21 in four North Carolina families, and a 4 bp deletion in the human distal-less 3 gene (DLX3) was identified in all affected members. A previous genetic linkage study in a large Virginia kindred with TDO indicated possible linkage to the ABO, Gc, and Kell blood group loci. To examine whether TDO exhibits genetic heterogeneity, we have performed molecular genetic analysis to determine whether affected members of this Virginia kindred have the DLX3 gene deletion identified in North Carolina families. Results show that affected subjects (n=3) from the Virginia family have the same four nucleotide deletion previously identified in the North Carolina families. A common haplotype for three genetic markers surrounding the DLX3 gene was identified in all affected subjects in the North Carolina and Virginia families. These findings suggest that all people with TDO who have been evaluated have inherited the same DLX3 gene deletion mutation from a common ancestor. The variable clinical phenotype observed in these North Carolina and Virginia families, which share a common gene mutation, suggests that clinical variability is not the result of genetic heterogeneity at the major locus, but may reflect genetic heterogeneity at other epigenetic loci or contributing environmental factors or both.

Sublocalization of the Papillon-Lefevre syndrome locus on 11q14-q21

Papillon-Lefevre syndrome (PLS) is an autosomal recessive form of palmoplantar ectodermal dysplasia, characterized by palmoplantar hyperkeratosis and severe early-onset periodontitis. The presence of severe periodontitis distinguishes PLS from other palmoplantar keratodermas. As part of our efforts to study the genetic basis of periodontitis susceptibility, we performed a genome-wide search to identify major loci for PLS in 44 individuals (14 affected) from 10 consanguineous PLS families. We have identified evidence for linkage of a PLS gene on 11q14-q21. A maximum two-point logarithm of the odds (LOD) score of 8.24 was obtained for D11S1367 at a recombination fraction of theta=0.00. Multipoint analysis resulted in a LOD score of 10.45 and placed the gene for PLS within a 4-5 cM genetic interval. This genetic interval, flanked by D11S4197 and D11S931, contains more than 50 cDNAs and 200 expressed sequence tags (ESTs). This refinement of the candidate region for a PLS gene is in agreement with other recent reports of linkage for PLS to chromosome 11q14-q21 and should help in identification of the gene for PLS.

Genetic linkage of hereditary gingival fibromatosis to chromosome 2p21

Gingival fibromatosis is characterized by a slowly progressive benign enlargement of the oral gingival tissues. The condition results in the teeth being partially or totally engulfed by keratinized gingiva, causing aesthetic and functional problems. Both genetic and pharmacologically induced forms of gingival fibromatosis are known. The most common genetic form, hereditary gingival fibromatosis (HGF), is usually transmitted as an autosomal dominant trait, although sporadic cases are common and autosomal recessive inheritance has been reported. The genetic basis of gingival fibromatosis is unknown. We identified an extended family (n=32) segregating an autosomal dominant form of isolated gingival fibromatosis. Using a genomewide search strategy, we identified genetic linkage (Zmax=5.05, straight theta=.00) for the HGF phenotype to polymorphic markers in the genetic region of chromosome 2p21 bounded by the loci D2S1788 and D2S441. This is the first report of linkage for isolated HGF, and the findings have implications for identification of the underlying genetic basis of gingival fibromatosis.

Identification of human plasma kallikrein gene polymorphisms and evaluation of their role in end-stage renal disease

Kallikreins are serine proteases that release kinins from kininogens. Kinins, via their effects on cardiovascular and renal function, may be involved in the pathogenesis of hypertension and renal failure. Two groups of kallikreins exist, glandular or tissue kallikrein and plasma kallikrein. In this study, we examined the human plasma kallikrein gene KLK3 to determine whether it contributed to end-stage renal disease (ESRD) susceptibility. We identified two novel polymorphic sequences closely linked to the KLK3 gene, designated KLK3b and KLK3c (heterozygosities: 0.64 to 0.68 and 0.48 to 0.52, respectively). We mapped the KLK3 gene and the marker KLK3c to the long arm of human chromosome 4 between F11 and D4S426 using a radiation hybrid panel. The study population consisted of 142 sibling pairs concordant for ESRD from 121 African American families. The 142 sibling pairs were stratified into 78 pairs with hypertension- and chronic glomerulonephritis-associated ESRD and 64 with non-insulin-dependent diabetes mellitus-associated ESRD. Linkage analyses, using SIBPAL of SAGE, and exclusion analysis, using MAPMAKERS/SIBS, were performed. Linkage analysis of affected sibling pairs did not reveal any evidence of linkage of KLK3 to ESRD in all 142 sib-pairs or in the two stratified subsets. Exclusion analysis indicated that the KLK3 gene could be excluded from contributing to ESRD at a relative risk of 3 when the maximum log of the odds score of -2 was used as the criterion for exclusion. However, an association analysis using the relative predispositional effect technique showed that alleles 7 and 9 of KLK3b were consistently associated with ESRD. Alleles 7 and 9 were present in 11.2% and 10.8% of the 113 unrelated ESRD probands and in 6.6% and 6.6% of the 204 race-matched control subjects without renal disease (allele P=.0041 and .0016, respectively). Alleles 7 and 9 were also present in 13% and 10.4% of the proband's first siblings (allele P=.00014 and .0087, respectively). The association of KLK3b alleles with ESRD raises the possibility that polymorphisms in KLK3 may play a role in ESRD susceptibility. The lack of linkage might reflect our relatively small family set.