An autosomal genomic scan for loci linked to prediabetic phenotypes in Pima Indians

J, Birznieks G, Chang J, Eldridge W, Erdos MR, Karanjawala ZE, Knapp JI, Kudelko K, Martin C, Morales-Mena A, Musick A, Musick T, Pfahl C, Porter R, Rayman JB, Rha D, Segal L, Shapiro S, Sharaf R, Shurtleff B, So A, Tannenbaum J, Te C, Tovar J, Unni A, Welch C, Whiten R, Witt A, Blaschak-Harvan J, Douglas JA, Duren WL, Epstein MP, Fingerlin TE, Kaleta HS, Lange EM, Li C, McEachin RC, Stringham HM, Trager E, White PP, Eriksson J, Toivanen L, Vidgren G, Nylund SJ, Tuomilehto-Wolf E, Ross EH, Demirchyan E, Hagopian WA, Buchanan TA, Tuomilehto J, Bergman RN, Collins FS, Boehnke M. The Finland-United States investigation of non-insulin-dependent diabetes mellitus genetics (FUSION) study. I. An autosomal genome scan for genes that predispose to type 2 diabetes

We performed a genome scan at an average resolution of 8 cM in 719 Finnish sib pairs with type 2 diabetes. Our strongest results are for chromosome 20, where we observe a weighted maximum LOD score (MLS) of 2.15 at map position 69.5 cM from pter and secondary weighted LOD-score peaks of 2.04 at 56.5 cM and 1.99 at 17.5 cM. Our next largest MLS is for chromosome 11 (MLS = 1.75 at 84.0 cM), followed by chromosomes 2 (MLS = 0.87 at 5.5 cM), 10 (MLS = 0.77 at 75.0 cM), and 6 (MLS = 0.61 at 112.5 cM), all under an additive model. When we condition on chromosome 2 at 8.5 cM, the MLS for chromosome 20 increases to 5.50 at 69.0 cM (P=.0014). An ordered-subsets analysis based on families with high or low diabetes-related quantitative traits yielded results that support the possible existence of disease-predisposing genes on chromosomes 6 and 10. Genomewide linkage-disequilibrium analysis using microsatellite marker data revealed strong evidence of association for D22S423 (P=.00007). Further analyses are being carried out to confirm and to refine the location of these putative diabetes-predisposing genes.

J, Birznieks G, Chang J, Eldridge W, Erdos MR, Karanjawala ZE, Knapp JI, Kudelko K, Martin C, Morales-Mena A, Musick A, Musick T, Pfahl C, Porter R, Rayman JB, Rha D, Segal L, Shapiro S, Sharaf R, Shurtleff B, So A, Tannenbaum J, Te C, Tovar J, Unni A, Welch C, Whiten R, Witt A, Kohtamäki K, Ehnholm C, Eriksson J, Toivanen L, Vidgren G, Nylund SJ, Tuomilehto-Wolf E, Ross EH, Demirchyan E, Hagopian WA, Buchanan TA, Tuomilehto J, Bergman RN, Collins FS, Boehnke M. The Finland-United States investigation of non-insulin-dependent diabetes mellitus genetics (FUSION) study. II. An autosomal genome scan for diabetes-related quantitative-trait loci

Type 2 diabetes mellitus is a complex disorder encompassing multiple metabolic defects. We report results from an autosomal genome scan for type 2 diabetes-related quantitative traits in 580 Finnish families ascertained for an affected sibling pair and analyzed by the variance components-based quantitative-trait locus (QTL) linkage approach. We analyzed diabetic and nondiabetic subjects separately, because of the possible impact of disease on the traits of interest. In diabetic individuals, our strongest results were observed on chromosomes 3 (fasting C-peptide/glucose: maximum LOD score [MLS] = 3.13 at 53.0 cM) and 13 (body-mass index: MLS = 3.28 at 5.0 cM). In nondiabetic individuals, the strongest results were observed on chromosomes 10 (acute insulin response: MLS = 3.11 at 21.0 cM), 13 (2-h insulin: MLS = 2.86 at 65.5 cM), and 17 (fasting insulin/glucose ratio: MLS = 3.20 at 9.0 cM). In several cases, there was evidence for overlapping signals between diabetic and nondiabetic individuals; therefore we performed joint analyses. In these joint analyses, we observed strong signals for chromosomes 3 (body-mass index: MLS = 3.43 at 59.5 cM), 17 (empirical insulin-resistance index: MLS = 3.61 at 0.0 cM), and 19 (empirical insulin-resistance index: MLS = 2.80 at 74.5 cM). Integrating genome-scan results from the companion article by Ghosh et al., we identify several regions that may harbor susceptibility genes for type 2 diabetes in the Finnish population.

Frequency of and interaction between polymorphisms in the beta3-adrenergic receptor and in uncoupling proteins 1 and 2 and obesity in Germans

OBJECTIVE

To determine the role of polymorphisms in the genes for beta3-adrenergic receptor (beta3-AR) and in uncoupling proteins 1 and 2 (UCP-1, UCP-2) in obesity.

DESIGN

Association study with three polymorphisms and obesity.

SUBJECTS

Two hundred and thirty-six morbidly obese patients who underwent gastric banding surgery, 381 patients from the medical clinic and 198 healthy blood donors.

MEASUREMENTS

The frequencies of the W64R in beta3-AR, the 3826A-->G in UCP-1 and the 45bp insertion in the 3 untranslated region of exon 8 in UCP-2 polymorphisms were determined.

RESULTS

There were no significant differences in the frequencies of the beta3-AR and UCP-1 polymorphisms between obese (body mass index, BMI > 30 kg/m2) and lean subjects. Lean, but not obese, carriers of the R allele of beta3-AR had a significantly higher BMI. The mean age of obese subjects (excluding diabetics) who were carriers of the G allele of the UCP-1 polymorphism, 36y, was significantly younger than wild-type, 40y (P= 0.007). This effect was not seen in lean subjects. The effect of the G allele on the mean age of obese subjects was more apparent in subjects who were also carriers of the R allele of the beta3-AR polymorphism. The frequency of the ins allele of UCP-2 was significantly higher in obese subjects, 0.31, than in lean, 0.24 (P= 0.002) and carriers of the ins allele had a significantly higher BMI, 38 vs 35 (P= 0.005). There was no association between any of the polymorphisms and type II diabetes.

CONCLUSION

In a German population, there was no association between the W64R in beta3-AR or the 3826A-->G in UCP-1 polymorphisms and obesity. However, they act synergistically to accelerate the development of obesity. The 45bp insertion in the 3 untranslated region of exon 8 in UCP-2 polymorphism is associated with obesity.

A calpain-10 gene polymorphism is associated with reduced muscle mRNA levels and insulin resistance

Previous linkage studies in Mexican-Americans localized a major susceptibility locus for type 2 diabetes, NIDDM1, to chromosome 2q. This evidence for linkage to type 2 diabetes was recently found to be associated with a common G-->A polymorphism (UCSNP-43) within the CAPN10 gene. The at-risk genotype was homozygous for the UCSNP-43 G allele. In the present study among Pima Indians, the UCSNP-43 G/G genotype was not associated with an increased prevalence of type 2 diabetes. However, Pima Indians with normal glucose tolerance, who have a G/G genotype at UCSNP-43, were found to have decreased rates of postabsorptive and insulin-stimulated glucose turnover that appear to result from decreased rates of glucose oxidation. In addition, G/G homozygotes were found to have reduced CAPN10 mRNA expression in their skeletal muscle. A decreased rate of insulin-mediated glucose turnover, or insulin resistance, is one mechanism by which the polymorphism in CAPN10 may increase susceptibility to type 2 diabetes mellitus in older persons.

EIF2AK3, encoding translation initiation factor 2-alpha kinase 3, is mutated in patients with Wolcott-Rallison syndrome

Wolcott-Rallison syndrome (WRS) is a rare, autosomal recessive disorder characterized by permanent neonatal or early infancy insulin-dependent diabetes. Epiphyseal dysplasia, osteoporosis and growth retardation occur at a later age. Other frequent multisystemic manifestations include hepatic and renal dysfunction, mental retardation and cardiovascular abnormalities. On the basis of two consanguineous families, we mapped WRS to a region of less than 3 cM on chromosome 2p12, with maximal evidence of linkage and homozygosity at 4 microsatellite markers within an interval of approximately 1 cM. The gene encoding the eukaryotic translation initiation factor 2-alpha kinase 3 (EIF2AK3) resides in this interval; thus we explored it as a candidate. We identified distinct mutations of EIF2AK3 that segregated with the disorder in each of the families. The first mutation produces a truncated protein in which the entire catalytic domain is missing. The other changes an amino acid, located in the catalytic domain of the protein, that is highly conserved among kinases from the same subfamily. Our results provide evidence for the role of EIF2AK3 in WRS. The identification of this gene may provide insight into the understanding of the more common forms of diabetes and other pathologic manifestations of WRS.

Associations between uncoupling protein 2, body composition, and resting energy expenditure in lean and obese African American, white, and Asian children

BACKGROUND

Little is known about genes that affect childhood body weight.

OBJECTIVE

The objective of this study was to examine the association between alleles of the mitochondrial uncoupling protein 2 (UCP2) gene and obesity because UCP2 may influence energy expenditure.

DESIGN

We related UCP2 genotype to body composition and resting energy expenditure in 105 children aged 6-10 y. Overweight children and nonoverweight children of overweight parents were genotyped for a 45-base pair deletion/insertion (del/ins) in 3'-untranslated region of exon 8 and for an exon 4 C to T transition.

RESULTS

Eighty-nine children were genotyped for the exon 8 allele: 50 children had del/del, 33 had del/ins, and 6 had ins/ins. Mean (+/-SD) body mass index (BMI; in kg/m(2)) was greater for children with del/ins (24.1 +/- 5.9) than for children with del/del (20.4 +/- 4.8; P < 0.001). BMI of ins/ins children (23.7 +/- 7.8) was not significantly different from that of del/ins children. A greater BMI in del/ins children was independent of race and sex. Body composition was also different according to UCP2 genotype. All body circumferences and skinfold thicknesses examined were significantly greater in del/ins than in del/del children. Body fat mass as determined by dual-energy X-ray absorptiometry was also greater in del/ins than in del/del children (P < 0.005). For 104 children genotyped at exon 4, no significant differences in BMI or body composition were found among the 3 exon 4 genotypes. Neither resting energy expenditure nor respiratory quotient were different according to UCP2 exon 4 or exon 8 genotype.

CONCLUSIONS

The exon 8 ins/del polymorphism of UCP2 appears to be associated with childhood-onset obesity. The UCP2/UCP3 genetic locus may play a role in childhood body weight.

Evidence of pleiotropic loci for fasting insulin, total fat mass, and abdominal visceral fat in a sedentary population: the HERITAGE family study

OBJECTIVE

To examine whether there is a major gene effect on fasting insulin and pleiotropic loci for fasting insulin, total fat mass (FM), and abdominal visceral fat (AVF).

RESEARCH METHODS AND PROCEDURES

A major gene hypothesis for fasting plasma insulin levels was assessed using segregation analyses of data on 495 members in 98 normolipidemic sedentary families of white descent who participated in the HERITAGE Family Study.

RESULTS

Segregation analyses were performed on insulin adjusted for age, on insulin adjusted for age and FM, and on insulin adjusted for age and AVF. Before adjustment for AVF and FM, a major gene effect on fasting insulin levels was indicated. The putative locus accounted for 54% of the variance under a recessive inheritance pattern, affecting 11% of the sample (i.e., allele frequency = 0.33). However, after adjusting for the effects of AVF or FM, neither a major effect alone nor a multifactorial component alone could be rejected, and support for a major gene was equivocal, i.e., neither the hypothesis of Mendelian tau values or that of the equal tau(s) were rejected and the equal tau model fit the data better than the Mendelian tau model. This pattern (i.e., major gene evidence for insulin before but not after adjustment for AVF or FM) suggests that there is a putative locus with pleiotropic effects on both insulin and FM and another pleiotropic locus for both insulin and AVF.

DISCUSSION

Although these data do not directly support an additional major gene for insulin independent of AVF and FM, such support cannot be ruled out because there is still a significant major effect on FM- or AVF-adjusted insulin (albeit the Mendelian nature of this effect is ambiguous).

Genome-wide search for genes related to the fat-free body mass in the Québec family study

Fat-free mass (FFM) consists mostly of skeletal muscle and bone tissues, and identification of the genes and molecular mechanisms involved in the control of FFM would have implications for the understanding of sarcopenia and potentially osteoporesis associated with aging, as well as the response to starvation, refeeding, anorexia, and any other conditions in which lean body mass is important. A genome-wide search for genes related to body leanness has been completed in the Quebec Family Study (QFS). Microsatellite markers (N = 292) from the 22 autosomal chromosomes were typed. The mean spacing of the markers was 11.9 centimorgans (cM) (range, <0.1 to 41). FFM was calculated from percent body fat, derived from underwater weighing, and body weight and was adjusted by regression for age and sex effects before analysis. A maximum of 336 sib pairs or 609 pairs of extended relatives were analyzed using single-point Haseman-Elston regression (SIBPAL and RELPAL) and multipoint variance component (SEGPATH) linkage analyses. Significant linkages were observed on chromosomes 15q25-q26 for a CA repeat within the insulin-like growth factor 1 receptor (IGF1R) gene (Lod score = 3.56) and at 18q12 with D18S877 (Lod score = 3.53) and D18S535 (Lod score = 3.58), 2 markers located 10 cM apart. A moderately significant linkage was also observed on chromosome 7p15.3 with the marker D7S1808 (Lod score = 2.72). The most obvious candidate genes within the regions identified by these linkages include the IGF1R on 15q and neuropeptide Y (NPY) and growth hormone-releasing hormone (GHRH) receptor on 7p. On 18q, the melanocortin receptor 4 (MC4R) is not likely the candidate gene for the observed linkage. This study represents the first genome-wide search for genes that may be involved in the regulation of the lean component of body mass in humans.

Human peroxisome proliferator activated receptor gamma coactivator 1 (PPARGC1) gene: cDNA sequence, genomic organization, chromosomal localization, and tissue expression

Brown adipose and muscle tissues can increase energy expenditure via adaptive thermogenesis, thereby protecting against obesity. Mouse peroxisome proliferator activated receptor gamma coactivator 1 (Pgc1) has been reported to enhance the expression of uncoupling protein-1, a key mediator of thermogenesis in brown adipose tissue (Puigserver et al., 1998, Cell 92, 829-839). We report here the characterization of the human PPARGC1 gene. PPARGC1 spans a genomic region of approximately 67 kb, is composed of 13 exons, and encodes a 91-kDa protein that exhibits 94% amino acid identity with the mouse ortholog. mRNA species, transcribed from the TATA-less promoter, are 6.4 and 5.3 kb in length due to utilization of two polyadenylation signals. Northern blotting revealed expression of both transcripts in heart, skeletal muscle, and kidney and to a lesser extent in liver, brain, and pancreas as well as in the perirenal adipose tissue of a pheochromocytoma patient. PPARGC1 was mapped to chromosome 4p15.1, a region that has been associated with basal insulin levels in Pima Indians. Hence, PPARGC1 expression might influence insulin sensitivity as well as energy expenditure, thereby contributing to the development and pathophysiology of human obesity.

Defective mutations in the insulin promoter factor-1 (IPF-1) gene in late-onset type 2 diabetes mellitus

Type 2 diabetes mellitus is a common disabling disease with onset in middle-aged individuals, caused by an imbalance between insulin production and action. Genetic studies point to major genetic components, but, with the exception of maturity-onset diabetes of the young (MODY), specific diabetes susceptibility genes remain to be identified. Recent studies showed that a dominant negative mutation in the insulin promoter factor-1 (IPF-1), a pancreatic beta-cell specific transcription factor, causes pancreatic agenesis and MODY. Thus, we investigated 192 French, non-MODY type 2 diabetic families for mutations in IPF-1. We identified 3 novel IPF-1 mutations, including 2 substitutions (Q59L and D76N) and an in-frame proline insertion (InsCCG243). Functional transactivation assays of these IPF-1 mutant isoforms in a beta-pancreatic tumor cell line transfected with a transcriptional reporter and IPF-1 expression plasmids demonstrate a significant inhibition of basal insulin promoter activity (stronger with the InsCCG243 mutant). We find that the InsCCG243 mutation is linked, in 2 families, to an autosomal dominant-like late-onset form of type 2 diabetes, in which insulin secretion becomes progressively impaired. The lower penetrance D76N and Q59L mutations were more prevalent and were associated with a relative risk of 12.6 for diabetes and with decreased glucose-stimulated insulin-secretion in nondiabetic subjects. We propose that IPF-1 mutations can cause MODY or apparently monogenic late-onset diabetes and that they represent a significant risk factor for type 2 diabetes in humans.

Testing the robustness of the likelihood-ratio test in a variance-component quantitative-trait loci-mapping procedure

Detection of linkage to genes for quantitative traits remains a challenging task. Recently, variance components (VC) techniques have emerged as among the more powerful of available methods. As often implemented, such techniques require assumptions about the phenotypic distribution. Usually, multivariate normality is assumed. However, several factors may lead to markedly nonnormal phenotypic data, including (a) the presence of a major gene (not necessarily linked to the markers under study), (b) some types of gene x environment interaction, (c) use of a dichotomous phenotype (i.e., affected vs. unaffected), (d) nonnormality of the population within-genotype (residual) distribution, and (e) selective (extreme) sampling. Using simulation, we have investigated, for sib-pair studies, the robustness of the likelihood-ratio test for a VC quantitative-trait locus-detection procedure to violations of normality that are due to these factors. Results showed (a) that some types of nonnormality, such as leptokurtosis, produced type I error rates in excess of the nominal, or alpha, levels whereas others did not; and (b) that the degree of type I error-rate inflation appears to be directly related to the residual sibling correlation. Potential solutions to this problem are discussed. Investigators contemplating use of this VC procedure are encouraged to provide evidence that their trait data are normally distributed, to employ a procedure that allows for nonnormal data, or to consider implementation of permutation tests.

Protein targeting to glycogen/PPP1R5: screening of coding and flanking genomic regions for polymorphisms and association analysis with insulin action in Pima Indians

Insulin resistance, a major predictor of type 2 diabetes mellitus, is genetically inherited in Pima Indians, a population with a high prevalence of the metabolically complex disease. Protein targeting to glycogen/PPP1R5 has recently been identified as a potential regulator of glycogen synthase, the rate-limiting enzyme of the insulin-induced glycogenesis. The gene is located on chromosome 10q23-24, where there is a suggestive linkage to insulin action in this population, establishing it as a functional and positional candidate gene. In this study, we discovered 2 novel polymorphisms upstream of the 5'UTR of the gene, with only one found in Pima Indians, but no polymorphism in the coding sequence. The genotype frequencies of the polymorphism and transcript levels of the gene in skeletal muscle do not correlate with insulin action in the subjects. These results exclude any significant role of protein targeting to glycogen/PPP1R5 in insulin resistance in Pima Indians.

Diagnosing diabetes mellitus

Diagnosing diabetes mellitus by well-defined, objectively established, laboratory criteria is a relatively recent occurrence. Diabetes was not defined by any laboratory criteria until urine glucose could be measured last century. The use of blood tests for glucose did not develop until well into this century. The discovery of insulin, the wider use of the hypodermic syringe for venesection and the development of micro methods for laboratory analysis permitted the development of blood tests in diagnosing diabetes. The use of insulin to keep young diabetic subjects alive, albeit with elevated glucose levels, lead to the discovery of the association of retinopathy and elevated plasma glucose. This lead to efforts to diagnose diabetes in as mild a form as possible using the oral glucose tolerance test, to prevent such complications occurring. Determining what glucose levels were normal or abnormal then became an issue. Studies of the Pima Indians of Arizona eventually lead to objective definitions of diabetes that have been further refined in the past few years. We also now understand how retinopathy and other diabetes complications may develop. It is the glucose itself 'sticking' to proteins (advanced glycosylation end products) that does the damage. The future holds the promise that genetic diagnoses for diabetes and its complications may lead to the total prevention of diabetes and its effects.

A gene encoding a transmembrane protein is mutated in patients with diabetes mellitus and optic atrophy (Wolfram syndrome)

Wolfram syndrome (WFS; OMIM 222300) is an autosomal recessive neurodegenerative disorder defined by young-onset non-immune insulin-dependent diabetes mellitus and progressive optic atrophy. Linkage to markers on chromosome 4p was confirmed in five families. On the basis of meiotic recombinants and disease-associated haplotypes, the WFS gene was localized to a BAC/P1 contig of less than 250 kb. Mutations in a novel gene (WFS1) encoding a putative transmembrane protein were found in all affected individuals in six WFS families, and these mutations were associated with the disease phenotype. WFS1 appears to function in survival of islet beta-cells and neurons.

An autosomal genomic scan for loci linked to type II diabetes mellitus and body-mass index in Pima Indians

Genetic factors influence the development of type II diabetes mellitus, but genetic loci for the most common forms of diabetes have not been identified. A genomic scan was conducted to identify loci linked to diabetes and body-mass index (BMI) in Pima Indians, a Native American population with a high prevalence of type II diabetes. Among 264 nuclear families containing 966 siblings, 516 autosomal markers with a median distance between adjacent markers of 6.4 cM were genotyped. Variance-components methods were used to test for linkage with an age-adjusted diabetes score and with BMI. In multipoint analyses, the strongest evidence for linkage with age-adjusted diabetes (LOD = 1.7) was on chromosome 11q, in the region that was also linked most strongly with BMI (LOD = 3.6). Bivariate linkage analyses strongly rejected both the null hypothesis of no linkage with either trait and the null hypothesis of no contribution of the locus to the covariation among the two traits. Sib-pair analyses suggest additional potential diabetes-susceptibility loci on chromosomes 1q and 7q.