Linkage of familial combined hyperlipidaemia to chromosome 1q21-q23

Hypertriglyceridemia-induced acute pancreatitis in children: A mini-review

Severe hypertriglyceridemia (HTG) is a known metabolic cause of acute pancreatitis (AP) in pediatric patients. The incidence of hypertriglyceridemia-induced acute pancreatitis (HTG-AP) is less well established in pediatric compared to adult patients. Studies in adults suggest that higher risk of AP occurs when triglyceride levels (TG) are >1,000 mg/dL. Most common etiologies for severe HTG in pediatric patients are either from primary hypertriglyceridemia, underlying genetic disorders of lipid and TG metabolism, or secondary hypertriglyceridemia, separate disease or exposure which affects TG metabolism. Most common theories for the pathophysiology of HTG-AP include hydrolysis of TG by pancreatic lipase to free fatty acids leading to endothelial and acinar cell damage and ischemia, as well as hyperviscosity related to increased chylomicrons. Though there are varying reports of HTG-AP severity compared to other causes of AP, a steadily growing body of evidence suggests that HTG-AP can be associated with more severe course and complications. Therapeutic interventions for HTG-AP typically involve inpatient management with dietary restriction, intravenous fluids, and insulin; select patients may require plasmapheresis. Long term interventions generally include dietary modification, weight management, control of secondary causes, and/or antihyperlipidemic medications. Though some therapeutic approaches and algorithms exist for adult patients, evidence-based management guidelines have not been well established for pediatric patients.

Association between Single-nucleotide Polymorphisms of RXRG and Genetic Susceptibility to Type 2 Diabetes in South China

OBJECTIVE

To investigate the relationship between genetic polymorphisms of RXRG rs1467664, rs3753898 and the genetic susceptibility of type 2 diabetes in the Chinese Han population from South China.

METHODS

In our case-control study, single-nucleotide polymorphisms (SNPs) rs1467664 and rs3753898 were genotyped by SNPscanTM kit in 1092 patients with T2D as cases and 1092 normal persons as controls. The distributions of genotype and allele frequencies in two groups were analyzed by the SPSS 20.0 software.

RESULTS

The distribution of genotypes and alleles of RXRG rs3753898 was statistically significant between the two groups, but there was no significant difference in the distribution of genotypes and alleles of the rs1467664. Before and after the adjustment of age, sex and BMI, rs3753898 in the two groups had statistical significance under the additive, dominant and recessive models (P<0.05), but no statistical differences were found under the overdominance and co-dominant genetic models (P>0.05). There was no significant difference in the genetic models of rs1467664 between the two groups (P>0.05). The haplotype, which consists of rs1467664 allele T and rs3753898 allele A was a high-risk factor for T2D, OR=1.27, 95% CI (1.09-1.47), Padj=0.002.

CONCLUSION

Our results showed that the single nucleotide polymorphism of RXRG rs3753898 may be related to genetic susceptibility of type 2 diabetes. The haplotype consisting of the allele T of rs1467664 and the allele A of rs3753898 is a risk factor for type 2 diabetes, suggesting that the genetic variation of RXRG gene may be the genetic cause of diabetes mellitus in the Chinese Han population.

Fluorescence Polarization-Based Bioassays: New Horizons

Fluorescence polarization holds considerable promise for bioanalytical systems because it allows the detection of selective interactions in real time and a choice of fluorophores, the detection of which the biosample matrix does not influence; thus, their choice simplifies and accelerates the preparation of samples. For decades, these possibilities were successfully applied in fluorescence polarization immunoassays based on differences in the polarization of fluorophore emissions excited by plane-polarized light, whether in a free state or as part of an immune complex. However, the results of recent studies demonstrate the efficacy of fluorescence polarization as a detected signal in many bioanalytical methods. This review summarizes and comparatively characterizes these developments. It considers the integration of fluorescence polarization with the use of alternative receptor molecules and various fluorophores; different schemes for the formation of detectable complexes and the amplification of the signals generated by them. New techniques for the detection of metal ions, nucleic acids, and enzymatic reactions based on fluorescence polarization are also considered.

Polymorphism rs3737787 of Upstream Stimulatory Factor 1 gene is associated with serum lipid phenotype in Nigerian population

Serum lipid profile which is determined by genotype-phenotype relationship plays a significant role in the development of cardiovascular disease. Upstream stimulatory factor 1 (USF1), has been reported to be associated with serum lipid levels in different population, hence, this study investigated the association of variants in USF1 with serum lipid profile in adults in Lagos state, Nigeria. We genotyped rs3737787 (11235C > T) and rs550376620 (10488G > A) with PCR-RFLP in 384 participants and we used logistic regression to assess the association of these variants with serum lipid levels. The minor allele frequency observed in 10488G > A in both case and control groups was 5% while the minor allele of 11235C > T was observed to be more frequent in the control when compared to the dyslipidemic subjects (24% vs 12%; p = 1.84e-05). Levels of total cholesterol, triglycerides, and LDL-c in dyslipidemic subjects with CC genotype of 11235C > T were significantly higher compared to CT and TT genotypes (p < 0.001; p < 0.0001 and p < 0.0001 respectively). Logistic regression with adjustment for age, gender and BMI, showed that the minor allele carriers of 11235C > T have a reduced risk of dyslipidemia (Odds ratio: 0. 0.043, 95% confidence interval (CI): (0.006-0.331, p = 0.002). Our findings revealed that rs3737787 is associated with lipid phenotype in Nigerian population.

Kbtbd11 contributes to adipocyte homeostasis through the activation of upstream stimulatory factor 1

The present study aimed to investigate the transcriptional regulation of Kbtbd11 in adipose tissue. To elucidate the physiological role of Kbtbd11 gene expression, adipose Kbtbd11 mRNA expression levels were estimated under various feeding states in wild-type mice. Kbtbd11 expression increased in a time-dependent manner in the adipose tissue in mice fed on chow diet, whereas the promotion of Kbtbd11 mRNA expression by refeeding was attenuated in mice fed on high-fat (HF) diet, suggesting the suppression of Kbtbd11 mRNA expression under HF diets and that changes in mRNA levels were associated with regulation of the transcription activity of Kbtbd11 by some transcription factors. To investigate the transcriptional regulation of Kbtbd11, the fragment upstream of either mouse Kbtbd11 or human KBTBD11 promoter was inserted into a luciferase vector. Luciferase reporter assays revealed that both mouse and human KBTBD11 promoter activity was increased by USF1. Direct USF1 binding to the Ebox in the Kbtbd11 promoter was confirmed by electrophoretic mobility shift and chromatin immunoprecipitation assays. In addition, the adipocyte differentiation marker levels increased instantly in Kbtbd11-overexpressing Usf1 knockdown cells than in Usf1 knockdown cells. These results imply an association of between Kbtbd11 with Usf1 expression and suggest the involvement of Kbtbd11 in a novel adipogenesis pathway.

A novel upstream transcription factor 1 target gene N4bp2l1 that regulates adipogenesis

N4BP2l1, which is highly expressed in oral squamous cell carcinoma, is associated with poor prognosis. However, N4bp2l1's role in adipogenesis remains unknown. We aimed to clarify the expression profile and transcriptional regulation of N4bp2l1 to elucidate the functions underlying the role of N4bp2l1 in adipocyte differentiation. Our results revealed that N4bp2l1 mRNA expression increased in 3T3-L1 cells in a differentiation-dependent manner. To investigate the transcriptional regulation of N4bp2l1, the 2-kb 5′ region upstream of the mouse N4bp2l1 promoter was cloned into a luciferase vector. Luciferase reporter assays indicated that USF1 induces the N4bp2l1 promoter activity. Electrophoretic mobility shift and chromatin immunoprecipitation assays confirmed that USF1 directly binds to the Ebox in the N4bp2l1 promoter. Furthermore, the expressions of adipocyte differentiation markers significantly decreased in N4bp2l1-knockdown cells compared with those in control cells. Our results demonstrated that N4bp2l1 is a novel USF1 target gene that may be involved in adipogenesis regulation.

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N4bp2l1 expression is increased in a differentiation-dependent manner in 3T3-L1.

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N4bp2l1 is a novel USF1 target gene.

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USF1 directly binds to the Ebox in the N4bp2l1 promoter.

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Inhibition of 3T3-L1 adipocyte differentiation by N4bp2l1 knockdown.

USF1 deficiency activates brown adipose tissue and improves cardiometabolic health

USF1 (upstream stimulatory factor 1) is a transcription factor associated with familial combined hyperlipidemia and coronary artery disease in humans. However, whether USF1 is beneficial or detrimental to cardiometabolic health has not been addressed. By inactivating USF1 in mice, we demonstrate protection against diet-induced dyslipidemia, obesity, insulin resistance, hepatic steatosis, and atherosclerosis. The favorable plasma lipid profile, including increased high-density lipoprotein cholesterol and decreased triglycerides, was coupled with increased energy expenditure due to activation of brown adipose tissue (BAT). Usf1 inactivation directs triglycerides from the circulation to BAT for combustion via a lipoprotein lipase-dependent mechanism, thus enhancing plasma triglyceride clearance. Mice lacking Usf1 displayed increased BAT-facilitated, diet-induced thermogenesis with up-regulation of mitochondrial respiratory chain complexes, as well as increased BAT activity even at thermoneutrality and after BAT sympathectomy. A direct effect of USF1 on BAT activation was demonstrated by an amplified adrenergic response in brown adipocytes after Usf1 silencing, and by augmented norepinephrine-induced thermogenesis in mice lacking Usf1. In humans, individuals carrying SNP (single-nucleotide polymorphism) alleles that reduced USF1 mRNA expression also displayed a beneficial cardiometabolic profile, featuring improved insulin sensitivity, a favorable lipid profile, and reduced atherosclerosis. Our findings identify a new molecular link between lipid metabolism and energy expenditure, and point to the potential of USF1 as a therapeutic target for cardiometabolic disease.

Triglyceride Treatment in the Age of Cholesterol Reduction

Cholesterol reduction has markedly reduced major cardiovascular disease (CVD) events and shown regression of atherosclerosis in some studies. However, CVD has for decades also been associated with increased levels of circulating triglyceride (TG)-rich lipoproteins. Whether this is due to a direct toxic effect of these lipoproteins on arteries or whether this is merely an association is unresolved. More recent genetic analyses have linked genes that modulate TG metabolism with CVD. Moreover, analyses of subgroups of hypertriglyceridemic (HTG) subjects in clinical trials using fibric acid drugs have been interpreted as evidence that TG reduction reduces CVD events. This review will focus on how HTG might cause CVD, whether TG reduction makes a difference, what pathophysiological defects cause HTG, and what options are available for treatment.

Assessment of cardiovascular disease risk factors in a genetically homogenous population of Parsi Zoroastrians in the United States: A pilot study

OBJECTIVE

Genetically isolated and homogenous populations are ideal for detecting genes underlying common complex diseases. The use of isolated populations with reduced disease heterogeneity has led to significant gene discoveries in the past. The aim of this pilot study was to assess the prevalence of cardiovascular disease (CVD) risk phenotypes in a genetically homogenous population of Parsi Zoroastrians in the United States.

METHODS

Anthropometrics, blood pressure, and medical history were collected from 152 men and 186 women participating in a pilot study as part of the Parsi Family Study. The relative pairs used in the study included 60 parent-off springs, 28 siblings, 6 grandparent-grandchild, 7 avuncular, 18 half-siblings, 7 half-avuncular, and one half-first cousin. Estimates of genetic and environmental influence were calculated using a maximum likelihood-based variance components method implemented in SOLAR.

RESULTS

The prevalence of overweight/obesity in adults (62%) was on par with current US prevalence. Hypertension and prehypertension were prevalent in 16% and 46% of the participants, respectively. The quantitative genetic analysis revealed significant heritabilities for all anthropometric phenotypes (P < 0.05). Significant phenotypic correlations were found between blood pressure and anthropometric phenotypes (P < 0.001), whereas significant genetic correlation was found for only diastolic blood pressure and fat free mass (rhoG  = -0.88, P < 0.05).

CONCLUSION

These preliminary data show significant additive genetic effects on CVD-related phenotypes in this population. Our findings represent the first epidemiological data in Parsi Zoroastrians in the United States and offer excellent promise for future genetic studies in this population. Am. J. Hum. Biol. 28:440-443, 2016. © 2016 Wiley Periodicals, Inc.

The rs2516839 Polymorphism of the USF1 Gene May Modulate Serum Triglyceride Levels in Response to Cigarette Smoking

Single nucleotide polymorphisms (SNPs) of the USF1 gene (upstream stimulatory factor 1) influence plasma lipid levels. This study aims to determine whether USF1 SNPs interact with traditional risk factors of atherosclerosis to increase coronary artery disease (CAD) risk. In the present study serum lipid levels and USF1 gene polymorphisms (rs2516839 and rs3737787) were determined in 470 subjects: 235 patients with premature CAD and 235 controls. A trend of increasing triglycerides (TG) levels in relation to the C allele dose of rs2516839 SNP was observed. The synergistic effect of cigarette smoking and C allele carrier state on CAD risk was also found (SIM = 2.69, p = 0.015). TG levels differentiated significantly particular genotypes in smokers (1.53 mmol/L for TT, 1.80 mmol/L for CT and 2.27 mmol/L for CC subjects). In contrast, these differences were not observed in the non-smokers subgroup (1.57 mmol/L for TT, 1.46 mmol/L for CT and 1.49 mmol/L for CC subjects). In conclusion, the rs2516839 polymorphism may modulate serum triglyceride levels in response to cigarette smoking. Carriers of the C allele seem to be particularly at risk of CAD, when exposed to cigarette smoking.

Primary hypertriglyceridemia in children and adolescents

Primary disorders of lipid metabolism causing hypertriglyceridemia (HyperTG) result from genetic defects in triglyceride synthesis and metabolism. With the exception of lipoprotein lipase deficiency, these primary HyperTG disorders usually present in adulthood. However, some are unmasked earlier by precipitating factors, such as obesity and insulin resistance, and can be diagnosed in adolescence. Physical findings may be present and can include eruptive, palmer, or tuberoeruptive xanthomas. Triglyceride levels are very high to severe and can occur in the absence or the presence of other lipid abnormalities. Each of the causes of HyperTG is associated with an increased risk to develop recurrent pancreatitis and some may increase the risk of premature cardiovascular disease. Adoption of a healthy lifestyle that includes a low-fat diet, optimizing body weight, smoking avoidance/cessation, and daily physical activity is the first line of therapy. Pharmacologic therapies are available and can be beneficial in select disorders. Here, we review the causes of primary HyperTG in children and adolescents, discuss their clinical presentation and associated complications including the risk of pancreatitis and premature cardiovascular disease, and conclude with management and novel therapies currently in development. The goal of this article is to provide a useful resource for clinicians who may encounter primary HyperTG in the pediatric population.

Next-generation gene discovery for variants of large impact on lipid traits

PURPOSE OF REVIEW

Detection of high-impact variants on lipid traits is complicated by complex genetic architecture. Although genome-wide association studies (GWAS) successfully identified many novel genes associated with lipid traits, it was less successful in identifying variants with a large impact on the phenotype. This is not unexpected, as the more common variants detectable by GWAS typically have small effects. The availability of large familial datasets and sequence data has changed the paradigm for successful genomic discovery of the novel genes and pathogenic variants underlying lipid disorders.

RECENT FINDINGS

Novel loci with large effects have been successfully mapped in families, and next-generation sequencing allowed for the identification of the underlying lipid-associated variants of large effect size. The success of this strategy relies on the simplification of the underlying genetic variation by focusing on large single families segregating extreme lipid phenotypes.

SUMMARY

Rare, high-impact variants are expected to have large effects and be more relevant for medical and pharmaceutical applications. Family data have many advantages over population-based data because they allow for the efficient detection of high-impact variants with an exponentially smaller sample size and increased power for follow-up studies.

Association of USF1 and APOA5 polymorphisms with familial combined hyperlipidemia in an Italian population

BACKGROUND

Familial combined hyperlipidemia (FCH) is a polygenic and multifactorial disease characterized by a variable phenotype showing increased levels of triglycerides and/or cholesterol. The aim of this study was to identify single nucleotides (SNPs) in lipid-related genes associated with FCH.

METHODS AND RESULTS

Twenty SNPs in lipid-related genes were studied in 142 control subjects and 165 FCH patients after excluding patients with mutations in the LDLR gene and patients with the E2/E2 genotype of APOE. In particular, we studied the 9996G > A (rs2073658) and 11235C > T (rs3737787) variants in the Upstream Stimulatory Factor 1 gene (USF1), and the -1131T > C (rs662799) and S19W (rs3135506) variants in the Apolipoprotein A-V gene (APOA5). We found that the frequencies of these variants differed between patients and controls and that are associated with different lipid profiles. At multivariate logistic regression SNP S19W in APOA5 remained significantly associated with FCH independently of age, sex, BMI, cholesterol and triglycerides.

CONCLUSIONS

Our results show that the USF1 and APOA5 polymorphisms are associated with FCH and that the S19W SNP in the APOA5 gene is associated to the disease independently of total cholesterol, triglycerides and BMI. However, more extensive studies including other SNPs such as rs2516839 in USF1, are required.

Genetic and environmental determinants of the susceptibility of Amerindian derived populations for having hypertriglyceridemia

Here, we discuss potential explanations for the higher prevalence of hypertriglyceridemia in populations with an Amerindian background. Although environmental factors are the triggers, the search for the ethnic related factors that explain the increased susceptibility of the Amerindians is a promising area for research. The study of the genetics of hypertriglyceridemia in Hispanic populations faces several challenges. Ethnicity could be a major confounding variable to prove genetic associations. Despite that, the study of hypertriglyceridemia in Hispanics has resulted in significant contributions. Two GWAS reports have exclusively included Mexican mestizos. Fifty percent of the associations reported in Caucasians could be generalized to the Mexicans, but in many cases the Mexican lead SNP was different than that reported in Europeans. Both reports included new associations with apo B or triglycerides concentrations. The frequency of susceptibility alleles in Mexicans is higher than that found in Europeans for several of the genes with the greatest effect on triglycerides levels. An example is the SNP rs964184 in APOA5. The same trend was observed for ANGPTL3 and TIMD4 variants. In summary, we postulate that the study of the genetic determinants of hypertriglyceridemia in Amerindian populations which have major changes in their lifestyle, may prove to be a great resource to identify new genes and pathways associated with hypertriglyceridemia.

Upstream Transcription Factor 1 (USF1) allelic variants regulate lipoprotein metabolism in women and USF1 expression in atherosclerotic plaque

Upstream transcription factor 1 (USF1) allelic variants significantly influence future risk of cardiovascular disease and overall mortality in females. We investigated sex-specific effects of USF1 gene allelic variants on serum indices of lipoprotein metabolism, early markers of asymptomatic atherosclerosis and their changes during six years of follow-up. In addition, we investigated the cis-regulatory role of these USF1 variants in artery wall tissues in Caucasians. In the Cardiovascular Risk in Young Finns Study, 1,608 participants (56% women, aged 31.9 ± 4.9) with lipids and cIMT data were included. For functional study, whole genome mRNA expression profiling was performed in 91 histologically classified atherosclerotic samples. In females, serum total, LDL cholesterol and apoB levels increased gradually according to USF1 rs2516839 genotypes TT < CT < CC and rs1556259 AA < AG < GG as well as according to USF1 H3 (GCCCGG) copy number 0 < 1 < 2. Furthermore, the carriers of minor alleles of rs2516839 (C) and rs1556259 (G) of USF1 gene had decreased USF1 expression in atherosclerotic plaques (P = 0.028 and 0.08, respectively) as compared to non-carriers. The genetic variation in USF1 influence USF1 transcript expression in advanced atherosclerosis and regulates levels and metabolism of circulating apoB and apoB-containing lipoprotein particles in sex-dependent manner, but is not a major determinant of early markers of atherosclerosis.

Association of RXR-Gamma Gene Variants with Familial Combined Hyperlipidemia: Genotype and Haplotype Analysis

Background. Familial combined hyperlipidemia (FCHL), the most common genetic form of hyperlipdemia, is characterized by a strong familial clustering and by premature coronary heart disease. The FCHL locus has been mapped to human chromosome 1q21-q23. This region includes the retinoid X receptor gamma (RXRG), a nuclear factor member of the RXR superfamily, which plays important roles in lipid homeostasis. Objective. To investigate the possible role of the RXRG gene in the genetic susceptibility to FCHL. Methods. Variations in RXRG gene were searched by direct sequencing, and the identified SNPs were genotyped by PCR-RFLP in 192 FCHL individuals from 74 families and in 119 controls. Results. We identified 5 polymorphisms in the RXRG gene (rs1128977, rs2651860, rs2134095, rs283696, and rs10918169). Genotyping showed that the A-allele of rs283696 SNP was significantly associated with FCHL (corrected P, P_c < 0.01). Also the alleles of the rs10918169 and of the rs2651860 SNP were more frequent in FCHL subjects compared to those in controls, although not significantly after correction. When the clinical characteristics of the FCHL subjects were stratified by allele carrier status for each SNP, the rs2651860 SNP was significantly associated with increased levels of LDL-cholesterol and of Apo-B in T-allele carriers (P < 0.04). Finally, haplotypes analysis with all 5 SNPs confirmed the significant association of RXRG gene with FCHL. Specifically, the haplotype containing all 3 “at-risk” alleles, significantly associated with FCHL (A-allele of rs283696, G-allele of rs10918169, and T-allele of rs2651860), showed an OR (Odds Ratio) of 2.02, P_c < 0.048. Conversely, the haplotype without all these 3 alleles was associated with a reduced risk for FCHL (OR = 0.39, P_c < 0.023). The “at-risk” haplotype CTTAG was also associated with higher LDL-C (P < 0.015). In conclusion, variation in the RXRG gene may contribute to the genetic dyslipidemia in FCHL subjects.

Abdominal Obesity and Expression of Familial Combined Hyperlipidemia

OBJECTIVE

To investigate the role of abdominal and body obesity on the prevalence of hyperlipidemia, in particular, hypertriglyceridemia, hypercholesterolemia, and high apolipoprotein B levels, in familial combined hyperlipidemia (FCHL) relatives and their spouses.

RESEARCH METHODS AND PROCEDURES

In FCHL relatives (n = 618) and spouses (n = 297), prevalence data of hyperlipidemia and high apolipoprotein B levels and their age and gender-corrected odds ratios (ORs) were calculated for sex-adjusted categories of waist-to-hip ratio (WHR), waist circumference, and BMI.

RESULTS

Increments of BMI, waist circumference, and WHR increased the frequency of hyperlipidemia. In the whole study population (relatives and spouses combined), frequency of hypertriglyceridemia showed a significant interaction only between WHR categories and FCHL. This was studied further after stratification of relatives by multivariable logistic regression analyses corrected for age and gender. Predominant expression of hypertriglyceridemia was observed with higher categories of WHR in FCHL relatives (prevalence up to 57.6%, OR 8.48 in highest vs. lowest WHR category, p < 0.001) but not in spouses (up to 32.9%, OR 1.05 in highest vs. lowest WHR category, not significant).

DISCUSSION

Both in spouses and FCHL relatives, increments in BMI and waist circumference increased the prevalence of hyperlipidemia. Specifically, in FCHL relatives, WHR was the most informative determinant of the expression of hyperlipidemia, in particular, hypertriglyceridemia. The data indicate that FCHL develops against a background of abdominal obesity.

Potential Role of Upstream Stimulatory Factor 1 Gene Variant in Familial Combined Hyperlipidemia and Related Disorders

Objective—

Genetic studies implicated upstream stimulatory factor 1 (USF1) in familial combined hyperlipidemia because the rs2073658 minor allele was associated with reduced risk of familial combined hyperlipidemia and related disorders. The molecular mechanisms whereby rs2073658 influences trait expression have remained elusive.

Methods and Results—

Plasma lipids, rs2073658 genotypes (N=372), and hepatic transcript levels (N=96) of USF1 and genes involved in hepatic lipoprotein production were determined in obese subjects. The rs2073658 minor allele was associated with reduced plasma triglycerides (TGs) ( P <0.001), hepatic USF1 ( P <0.01), and microsomal TG transfer protein transcript levels ( P <0.05). Functional studies in human hepatocellular carcinoma cells showed that rs2073658 is located in a forkhead box A2 (FOXA2) binding site and that major allele constructs displayed higher transcriptional activity than minor allele constructs. Knockdown of FOXA2 reduced the activity of major, but not minor allele constructs. Furthermore, an interaction between hepatic FOXA2 transcript levels and rs2073658 minor allele carrier status on hepatic USF1 transcript levels was observed in vivo ( P <0.05). USF1 activated the transcription of FOXA2 and FOXA2 strongly activated the transcription of microsomal TG transfer protein.

Conclusion—

A feed-forward loop comprising activation of USF1 transcription by FOXA2 and activation of FOXA2 transcription by USF1 , driving microsomal TG transfer protein expression, is modulated by rs2073658. Hence, rs2073658 likely influences hepatic TG secretion.

Physical, Social and Cultural, and Global Influences

In Chap. 5, we examined the technological environment of the health care policy-making system. Specifically, we examined the classification, evolution, and diffusion of medical technology; the effects of medical technology on medical training and the practice of medicine; effects on medical costs, quality of care, and quality of life; effects on access to care; the ethical concerns raised by medical technology; and the practice of technology assessment. We concluded the chapter by observing that the growth of technology, as well as other human endeavors, affects other important aspects of our lives, most notably, the air we breathe, the food we eat, the generation of radioactive by-products and toxic chemicals, the manufacture of illicit drugs, and the generation of natural and man-made hazards. In other words, in addition to their effects on the health care system, technology and other human activities affect many other aspects of our lives that are associated with health.

Novel drugs in familial combined hyperlipidemia: lessons from type 2 diabetes mellitus

PURPOSE OF REVIEW

Familial combined hyperlipidemia (FCHL) and type 2 diabetes mellitus (T2DM) are prevalent entities that share many features of the metabolic syndrome. Recent findings suggest that FCHL and T2DM are less distinct than initially anticipated, which could offer new insights for their therapeutic approach.

RECENT FINDINGS

Genetic association studies have provided evidence for a common genetic background (upstream transcription factor 1, activating transcription factor 6, transcription factor 7-like 2 and hepatocyte nuclear factor 4 alpha) between FCHL and T2DM. The metabolic overlap can be illustrated by the presence of ectopic fat accumulation and insulin resistance (muscle, adipose tissue and liver). We have shown that FCHL patients are at increased risk to develop T2DM. This indicates that both entities are not static, but instead the former is able to migrate to the latter as insulin resistance progresses. Given these new findings, it can be anticipated that FCHL patients could also benefit from insulin-sensitizing therapy such as pioglitazone and metformin. Indeed, pilot studies have demonstrated that pioglitazone might be advantageous in FCHL patients.

SUMMARY

Recent studies suggest that FCHL patients have an increased risk to develop T2DM, which has important clinical implications. Further studies are necessary to evaluate whether FCHL patients can be protected from new-onset T2DM and premature cardiovascular events with insulin-sensitizing therapy.

Upstream transcription factor 1 influences plasma lipid and metabolic traits in mice

Upstream transcription factor 1 (USF1) has been associated with familial combined hyperlipidemia, the metabolic syndrome, and related conditions, but the mechanisms involved are unknown. In this study, we report validation of Usf1 as a causal gene of cholesterol homeostasis, insulin sensitivity and body composition in mouse models using several complementary approaches and identify associated pathways and gene expression network modules. Over-expression of human USF1 in both transgenic mice and mice with transient liver-specific over-expression influenced metabolic trait phenotypes, including obesity, total cholesterol level, LDL/VLDL cholesterol and glucose/insulin ratio. Additional analyses of trait and hepatic gene expression data from an F2 population derived from C57BL/6J and C3H/HeJ strains in which there is a naturally occurring variation in Usf1 expression supported a causal role for Usf1 for relevant metabolic traits. Gene network and pathway analyses of the liver gene expression signatures in the F2 population and the hepatic over-expression model suggested the involvement of Usf1 in immune responses and metabolism, including an Igfbp2-centered module. In all three mouse model settings, notable sex specificity was observed, consistent with human studies showing differences in association with USF1 gene polymorphisms between sexes.

Identification of two common variants contributing to serum apolipoprotein B levels in Mexicans

BACKGROUND AND PURPOSE

Although the Mexican population has a high predisposition to dyslipidemias and premature coronary artery disease, this population is underinvestigated for the genetic factors conferring the high susceptibility. This study attempted to determine these genetic factors.

METHODS AND RESULTS

First, we investigated apolipoprotein B (apoB) levels in Mexican extended families with familial combined hyperlipidemia using a two-step testing strategy. In the screening step, we screened 5721 single-nucleotide polymorphisms (SNPs) for linkage signals with apoB. In the test step, we analyzed the 130 SNPs residing in regions of suggestive linkage signals for association with apoB. We identified significant associations with two SNPs (ie, rs1424032 [P=6.07x10(-6)] and rs1349411 [P=2.72x10(-4)]) that surpassed the significance level for the number of tests performed in the test step (P<3.84x10(-4)). Second, these SNPs were tested for replication in Mexican hyperlipidemic case-control samples. The same risk alleles as in the families with familial combined hyperlipidemia were significantly associated (P<0.05) with apoB in the case-control samples. The rs1349411 resides near the apoB messenger RNA editing enzyme (APOBEC1) involved in the processing of APOB messenger RNA in the small intestine. The rs1424032 resides in a highly conserved noncoding region predicted to function as a regulatory element.

CONCLUSIONS

We identified two novel variants, rs1349411 and rs1424032, for serum apoB levels in Mexicans.

A systems genetics approach implicates USF1, FADS3, and other causal candidate genes for familial combined hyperlipidemia

We hypothesized that a common SNP in the 3' untranslated region of the upstream transcription factor 1 (USF1), rs3737787, may affect lipid traits by influencing gene expression levels, and we investigated this possibility utilizing the Mexican population, which has a high predisposition to dyslipidemia. We first associated rs3737787 genotypes in Mexican Familial Combined Hyperlipidemia (FCHL) case/control fat biopsies, with global expression patterns. To identify sets of co-expressed genes co-regulated by similar factors such as transcription factors, genetic variants, or environmental effects, we utilized weighted gene co-expression network analysis (WGCNA). Through WGCNA in the Mexican FCHL fat biopsies we identified two significant Triglyceride (TG)-associated co-expression modules. One of these modules was also associated with FCHL, the other FCHL component traits, and rs3737787 genotypes. This USF1-regulated FCHL-associated (URFA) module was enriched for genes involved in lipid metabolic processes. Using systems genetics procedures we identified 18 causal candidate genes in the URFA module. The FCHL causal candidate gene fatty acid desaturase 3 (FADS3) was associated with TGs in a recent Caucasian genome-wide significant association study and we replicated this association in Mexican FCHL families. Based on a USF1-regulated FCHL-associated co-expression module and SNP rs3737787, we identify a set of causal candidate genes for FCHL-related traits. We then provide evidence from two independent datasets supporting FADS3 as a causal gene for FCHL and elevated TGs in Mexicans.

By integrating a genetic polymorphism with genome-wide gene expression levels, we were able to attribute function to a genetic polymorphism in the USF1 gene. The USF1 gene has previously been associated with a common dyslipidemia, FCHL. FCHL is characterized by elevated levels of total cholesterol, triglycerides, or both. We demonstrate that this genetic polymorphism in USF1 contributes to FCHL disease risk by modulating the expression of a group of genes functionally related to lipid metabolism, and that this modulation is mediated by USF1. One of the genes whose expression is modulated by USF1 is FADS3, which was also implicated in a recent genome-wide association study for lipid traits. We demonstrated that a genetic polymorphism from the FADS3 region, which was associated with triglycerides in a GWAS study of Caucasians, was also associated with triglycerides in Mexican FCHL families. Our analysis provides novel insight into the gene expression profile contributing to FCHL disease risk, and identifies FADS3 as a new gene for FCHL in Mexicans.

Genetic variation at the proprotein convertase subtilisin/kexin type 5 gene modulates high-density lipoprotein cholesterol levels

BACKGROUND

A low level of plasma high-density lipoprotein cholesterol (HDL-C) is a risk factor for cardiovascular disease. HDL particles are modulated by a variety of lipases, including endothelial lipase, a phospholipase present on vascular endothelial cells. The proprotein convertase subtilisin/kexin type 5 (PCSK5) gene product is known to directly inactivate endothelial lipase and indirectly cleave and activate angiopoetin-like protein 3, a natural inhibitor of endothelial lipase. We therefore investigated the effect of human PCSK5 genetic variants on plasma HDL-C levels.

METHODS AND RESULTS

Haplotypes at the PCSK5 locus were examined in 9 multigenerational families that included 60 individuals with HDL-C <10th percentile. Segregation with low HDL-C in 1 family was found. Sequencing of the PCSK5 gene in 12 probands with HDL-C <5th percentile identified 7 novel variants. Using a 2-stage design, we first genotyped these single-nucleotide polymorphisms (SNPs) along with 163 tagSNPs and 12 additional SNPs (n=182 total) in 457 individuals with documented coronary artery disease. We identified 9 SNPs associated with HDL-C (P<0.05), with the strongest results for rs11144782 and rs11144766 (P=0.002 and P=0.005, respectively). The SNP rs11144782 was also associated with very low-density lipoprotein (P=0.039), triglycerides (P=0.049), and total apolipoprotein levels (P=0.022). In stage 2, we replicated the association of rs11144766 with HDL-C (P=0.014) in an independent sample of Finnish low HDL-C families. In a combined analysis of both stages (n=883), region-wide significance of rs11144766 and low HDL-C was observed (unadjusted P=1.86x10(-4) and Bonferroni-adjusted P=0.031).

CONCLUSIONS

We conclude that variability at the PCSK5 locus influences HDL-C levels, possibly through the inactivation of endothelial lipase activity, and, consequently, atherosclerotic cardiovascular disease risk.

Retinoid X receptor heterodimer variants and cardiovascular risk factors

Nuclear receptors are transcription factors that can be activated by specific ligands. Recent progress has shown that retinoid X receptor (RXR) and its heterodimerization partners, including peroxisome proliferator-activated receptors, regulate many important genes involved in energy homeostasis and atherosclerosis, and should be promising therapeutic targets of metabolic syndrome. RXR heterodimers regulate a number of complex cellular processes, and genetic studies of RXR heterodimers have provided important clinical information in addition to knowledge gained from basic research. Genetic variants of RXR heterodimers were screened and investigated, and some variants were shown to have a considerable impact on metabolic disorders, including phenotypic components of familial combined hyperlipidemia. The combined efforts of basic and clinical science regarding nuclear receptors have achieved significant progress in unraveling the inextricably linked control system of energy expenditure, lipid and glucose homeostasis, inflammation, and atherosclerosis.This review summarizes the current understanding regarding RXR heterodimers based on their human genetic variants, which will provide new clues to uncover the background of multifactorial disease, such as metabolic syndrome or familial combined hyperlipidemia.

OSBPL10, a novel candidate gene for high triglyceride trait in dyslipidemic Finnish subjects, regulates cellular lipid metabolism

Analysis of variants in three genes encoding oxysterol-binding protein (OSBP) homologues (OSBPL2, OSBPL9, OSBPL10) in Finnish families with familial low high-density lipoprotein (HDL) levels (N = 426) or familial combined hyperlipidemia (N = 684) revealed suggestive linkage of OSBPL10 single-nucleotide polymorphisms (SNPs) with extreme end high triglyceride (TG; >90th percentile) trait. Prompted by this initial finding, we carried out association analysis in a metabolic syndrome subcohort (Genmets) of Health2000 examination survey (N = 2,138), revealing association of multiple OSBPL10 SNPs with high serum TG levels (>95th percentile). To investigate whether OSBPL10 could be the gene underlying the observed linkage and association, we carried out functional experiments in the human hepatoma cell line Huh7. Silencing of OSBPL10 increased the incorporation of [(3)H]acetate into cholesterol and both [(3)H]acetate and [(3)H]oleate into triglycerides and enhanced the accumulation of secreted apolipoprotein B100 in growth medium, suggesting that the encoded protein ORP10 suppresses hepatic lipogenesis and very-low-density lipoprotein production. ORP10 was shown to associate dynamically with microtubules, consistent with its involvement in intracellular transport or organelle positioning. The data introduces OSBPL10 as a gene whose variation may contribute to high triglyceride levels in dyslipidemic Finnish subjects and provides evidence for ORP10 as a regulator of cellular lipid metabolism.

Upstream transcription factor 1 (USF1) in risk of type 2 diabetes: association study in 2000 Dutch Caucasians

Type 2 diabetes shares substantial genetic and phenotypic overlap with familial combined hyperlipidemia. Upstream stimulatory factor 1 (USF1), a well-established susceptibility gene for familial combined hyperlipidemia, is postulated to be such a shared genetic determinant. We evaluated two established variants in familial combined hyperlipidemia (rs2073658 and rs3737787) for association with type 2 diabetes in two Dutch case-control samples (N=2011). The first case-control sample comprised 501 subjects with type 2 diabetes from the Breda cohort and 920 healthy blood bank donors of Dutch Caucasian origin. The second case-control sample included 211 subjects with type 2 diabetes, and 379 normoglycemic controls. SNP rs2073658 and SNP rs3737787 were in perfect linkage disequilibrium. In the first case-control sample, prevalence of the major allele was higher in patients than in controls (75% versus 71%, OR=1.25, p=0.018). A similar effect-size and -direction was observed in the second case-control sample (76% versus 72%, OR=1.22, p=0.16). A combined analysis strengthened the evidence for association (OR=1.23, p=0.006). Notably, the increased risk for type 2 diabetes could be ascribed to the major allele, and its high frequency translated to a substantial population attributable risk of 14.5%. In conclusion, the major allele of rs2073658 in the USF1 gene is associated with a modestly increased risk to develop type 2 diabetes in Dutch Caucasians, with considerable impact at the population level.

Biochemical and structural characterization of apolipoprotein A-I binding protein, a novel phosphoprotein with a potential role in sperm capacitation

The physiological changes that sperm undergo in the female reproductive tract rendering them fertilization-competent constitute the phenomenon of capacitation. Cholesterol efflux from the sperm surface and protein kinase A (PKA)-dependent phosphorylation play major regulatory roles in capacitation, but the link between these two phenomena is unknown. We report that apolipoprotein A-I binding protein (AI-BP) is phosphorylated downstream to PKA activation, localizes to both sperm head and tail domains, and is released from the sperm into the media during in vitro capacitation. AI-BP interacts with apolipoprotein A-I, the component of high-density lipoprotein involved in cholesterol transport. The crystal structure demonstrates that the subunit of the AI-BP homodimer has a Rossmann-like fold. The protein surface has a large two compartment cavity lined with conserved residues. This cavity is likely to constitute an active site, suggesting that AI-BP functions as an enzyme. The presence of AI-BP in sperm, its phosphorylation by PKA, and its release during capacitation suggest that AI-BP plays an important role in capacitation possibly providing a link between protein phosphorylation and cholesterol efflux.

Association of stearoyl-CoA desaturase 1 activity with familial combined hyperlipidemia

OBJECTIVE

Stearoyl-CoA desaturase 1 (SCD1) is the rate-limiting enzyme involved in the synthesis of monounsaturated fatty acids, and in mice SCD1 activity is associated with plasma triglyceride levels. We used the fatty acid desaturation index (the plasma ratio of 18:1/18:0) as a marker of SCD1 activity to investigate the relationship of SCD1 to familial combined hyperlipidemia (FCHL).

METHODS AND RESULTS

The fatty acid desaturation index was measured in 400 individuals from 18 extended FCHL pedigrees. FCHL-affected individuals exhibited increased SCD1 activity when compared to unrelated controls (P < 0.0001). The fatty acid desaturation index was found to be highly heritable (h(2) = 0.48, P = 2.2 x 10(-11)) in this study sample. QTL analysis in 346 sibling pairs from 18 FCHL families revealed suggestive linkage of the desaturation index to chromosomes 3p26.1 to 3p13 (z = 2.7, P = 0.003), containing the peroxisome proliferator-activated receptor gamma (PPARgamma) gene, and 20p11.21 to 20q13.32 (z = 1.7, P = 0.04), containing the hepatocyte nuclear factor 4, alpha (HNF4alpha) gene. A specific haplotype of HNF4alpha was found to be associated with the desaturation index in these FCHL families (P = 0.002).

CONCLUSIONS

Our results demonstrate that the fatty acid desaturation index is a highly heritable trait that is associated with the dyslipidemia observed in FCHL.

TCF7L2 is associated with high serum triacylglycerol and differentially expressed in adipose tissue in families with familial combined hyperlipidaemia

AIMS/HYPOTHESIS

Common DNA variants of the transcription factor 7-like 2 gene (TCF7L2) are associated with type 2 diabetes. Familial combined hyperlipidaemia (FCHL) is characterised by hypertriacylglycerolaemia, hypercholesterolaemia, or both. Additionally, disturbances in glucose metabolism are commonly seen in FCHL. Therefore, we hypothesised that TCF7L2 may contribute to the genetic susceptibility for this common dyslipidaemia.

METHODS

We investigated the effect of the TCF7L2 variants, rs7903146 and rs12255372, on FCHL and its component traits triacylglycerol (TG), total cholesterol (TC) and apolipoprotein B (ApoB) in 759 individuals from 55 Mexican families. As a replication sample, 719 individuals from 60 Finnish FCHL families were analysed. We also used quantitative RT-PCR to evaluate the transcript levels of TCF7L2 in 47 subcutaneous fat biopsies from unrelated Mexican FCHL and normolipidaemic participants.

RESULTS

Significant evidence for association was observed for high TG for the T alleles of rs7903146 and rs12255372 (p = 0.005 and p = 0.01) in Mexican FCHL families. No evidence for association was observed for FCHL, TC, ApoB or glucose in Mexicans. When testing rs7903146 and rs12255372 for replication in Finnish FCHL families, these single nucleotide polymorphisms were associated with TG (p = 0.01 and p = 0.007). Furthermore, we observed statistically significant decreases in the mRNA levels (p = 0.0002) of TCF7L2 in FCHL- and TG-affected individuals. TCF7L2 expression was not altered by the SNP genotypes.

CONCLUSIONS/INTERPRETATION

These data show that rs7903146 and rs12255372 are significantly associated with high TG in FCHL families from two different populations. In addition, significantly decreased expression of TCF7L2 was observed in TG- and FCHL-affected individuals.

Association of a polymorphism in the promoter of the cellular retinoic acid-binding protein II gene (CRABP2) with increased circulating low-density lipoprotein cholesterol

BACKGROUND

The cellular retinoic acid-binding protein II (CRABP-II), together with nuclear receptors such as the retinoid X receptor (RXR) and retinoic acid receptor (RAR), is involved in the transcriptional regulation of genes that control lipid metabolism via the retinoid signaling pathway and, as such, may be associated with disorders of lipid metabolism. Interestingly, the gene for CRABP-II is located on chromosome 1q21-23, which is a region that has been linked with disorders such as familial combined hyperlipidemia (FCHL), type 2 diabetes mellitus, and partial lipodystrophy, all of which are characterized by dyslipidemia.

METHODS

We investigated the hypothesis that the CRABP2 gene is involved in the regulation of lipid metabolism. Using the promoter -394T>C polymorphism of the CRABP2 gene, we performed association studies in three different cohorts: 299 healthy males, 182 HIV-infected patients and 151 patients with familial hypercholesterolemia (FH). All cholesterol measurements were performed in the absence of any lipid-lowering agents. ANOVA was performed on data adjusted for age, body mass index (BMI), gender, and use of protease inhibitors.

RESULTS

The frequency of the C allele was 0.03 in the three groups. Among healthy males, carriers of the C allele had 9% higher total plasma cholesterol (p=0.027) and 13% higher low-density lipoprotein cholesterol (LDL-C) concentrations (p=0.020). In HIV-infected patients, multivariate analysis of four measures over a 1-year period showed that carriers of the C allele had significantly higher LDL-C of between 10% and 31% (p=0.001) compared with non-carriers of the allele. FH patients who were carriers of the C allele had 16% higher LDL-C (p=0.038). The C allele was significantly over-represented among hypercholesterolemic patients (p=0.001).

CONCLUSIONS

Our results show that the CRABP2 gene, a member of the retinoid signaling pathway, is associated with increased plasma LDL-C concentrations.

Migraine: a complex genetic disorder

Although family and twin studies show that there is a genetic component to migraine, no genes predisposing to common forms of the disorder have been identified. The most encouraging findings have emerged from the identification of genes causing rare mendelian traits that phenotypically resemble migraine. These studies have pointed migraine research towards ion-transport genes; however, there is no direct evidence of the involvement of these genes in common forms of migraine. Family-based linkage studies have identified several chromosomal regions linked to common forms of migraine, but there is little consistency between studies. The modest success in the identification of contributing gene variants has stimulated research into more effective strategies. These include new phenotyping methods for genetic studies and new study designs-such as case-control and whole-genome association studies-to identify common variants contributing to the trait.

Genetic variation in thioredoxin interacting protein (TXNIP) is associated with hypertriglyceridaemia and blood pressure in diabetes mellitus

AIMS

Thioredoxin interacting protein (TXNIP) is an attractive candidate gene for diabetes or diabetic dyslipidaemia, since TXNIP is the strongest glucose-responsive gene in pancreatic B-cells, TXNIP deficiency in a mouse model is associated with hyperlipidaemia and TXNIP is located in the 1q21-1q23 chromosomal Type 2 diabetes mellitus (DM) locus. We set out to investigate whether metabolic effects of TXNIP that were previously reported in a murine model are also relevant in human Type 2 DM.

METHODS

The frequency distribution of a 3' UTR single nucleotide polymorphism (SNP) in TXNIP was investigated in subjects with normal glucose tolerance (NGT; n = 379), impaired glucose tolerance (IGT; n = 228) and Type 2 DM (n = 230). Metabolic data were used to determine the effect of this SNP on parameters associated with lipid and glucose metabolism.

RESULTS

The frequency of the TXNIP variation did not differ between groups, but within the group of diabetic subjects, carriers of the TXNIP-T variant had 1.6-fold higher triglyceride concentrations (P = 0.015; n = 136) and a 5.5-mmHg higher diastolic blood pressure (P = 0.02; n = 212) than homozygous carriers of the common C-allele, whereas in non-diabetic subjects fasting glucose was 0.26 mmol/l lower (P = 0.002; n = 478) in carriers of the T-allele. Moreover, a significant interaction between plasma glucose concentrations and TXNIP polymorphism on plasma triglycerides was observed (P = 0.012; n = 544).

CONCLUSION

This is the first report to implicate TXNIP in a human disorder of energy metabolism, Type 2 diabetes. The effect of TXNIP on triglycerides is influenced by plasma glucose concentrations, suggesting that the biological relevance of TXNIP variations may be particularly relevant in recurrent episodes of hyperglycaemia.

High Frequency of a Retinoid X Receptor γ Gene Variant in Familial Combined Hyperlipidemia That Associates With Atherogenic Dyslipidemia

OBJECTIVE

The genetic background of familial combined hyperlipidemia (FCHL) has not been fully clarified. Because several nuclear receptors play pivotal roles in lipid metabolism, we tested the hypothesis that genetic variants of nuclear receptors contribute to FCHL.

METHODS AND RESULTS

We screened all the coding regions of the PPARalpha, PPARgamma2, PPARdelta, FXR, LXRalpha, and RXRgamma genes in 180 hyperlipidemic patients including 60 FCHL probands. Clinical characteristics of the identified variants were evaluated in other 175 patients suspected of coronary disease. We identified PPARalpha Asp140Asn and Gly395Glu, PPARgamma2 Pro12Ala, RXRgamma Gly14Ser, and FXR -1g->t variants. Only RXRgamma Ser14 was more frequent in FCHL (15%, P<0.05) than in other primary hyperlipidemia (4%) and in controls (5%). Among patients suspected of coronary disease, we identified 9 RXRgamma Ser14 carriers, who showed increased triglycerides (1.62+/-0.82 versus 1.91+/-0.42 [mean+/-SD] mmol/L, P<0.05), decreased HDL-cholesterol (1.32+/-0.41 versus 1.04+/-0.26, P<0.05), and decreased post-heparin plasma lipoprotein lipase protein levels (222+/-85 versus 149+/-38 ng/mL, P<0.01). In vitro, RXRgamma Ser14 showed significantly stronger repression of the lipoprotein lipase promoter than RXRgamma Gly14.

CONCLUSION

These findings suggest that RXRgamma contributes to the genetic background of FCHL.

Apolipoprotein E polymorphism influences lipid phenotypes in Chinese families with familial combined hyperlipidemia

BACKGROUND

Apolipoprotein E (apoE) polymorphism is associated with changes in the lipoprotein profile of individuals with familial combined hyperlipidemia (FCHL), but its effects on the lipoprotein profiles of members of Chinese families with FCHL remain uncertain.

METHODS AND RESULTS

43 FCHL families (n=449) and 9 normolipidemic families (n=73) were recruited to assess the influence of apoE polymorphism on plasma lipids. The relative frequency of the epsilon4 allele in affected and unaffected FCHL relatives, spouses and normolipidemic members was 13.8%, 5.3%, 9.1% and 6.8%, respectively, with a significantly higher frequency in affected FCHL relatives, compared with unaffected FCHL relatives or normolipidemic members (p=0.0002 or p=0.029). In FCHL relatives, the apoE4 subset (E4/4 and E4/3) exhibited significantly higher levels of apoB, total cholesterol and low-density lipoprotein-cholesterol (LDL-C) than did the apoE3 (E3/3) subset, especially in women (all p<0.05), and there was significant elevation of LDL-C concentrations in men only (p<0.05). In men, the apoE2 (E3/2) subset indicated a decreased level of apoB and increased apoA1 compared with those in the apoE3 subset (p<0.05).

CONCLUSIONS

ApoE polymorphism appears to be associated with variance of the lipoprotein phenotype in Chinese families with FCHL.

Serum lipids in the GENECARD study of coronary artery disease identify quantitative trait loci and phenotypic subsets on chromosomes 3q and 5q

Coronary artery disease (CAD) and dyslipidemia have strong genetic components. Heterogeneity complicates evaluating genetics of complex diseases such as CAD; incorporating disease-related phenotypes may help reduce heterogeneity. We hypothesized that incorporating lipoproteins in a study of CAD would increase the power to map genes, narrow linkage peaks, identify phenotypic subsets, and elucidate the contribution of established risk factors to genetic results. We performed ordered subset analysis (OSA) and quantitative trait linkage (QTL) using serum lipoproteins and microsatellite markers in 346 families with early-onset CAD. OSA defined homogeneous subsets and calculated lod scores across a chromosome after ranking families by mean lipoprotein values. QTL used variance components analysis. We found significantly increased linkage to chromosome 3q13 (LOD 5.10, p = 0.008) in families with higher HDL cholesterol, lower LDL and total cholesterol, lower triglycerides, and fewer CAD risk factors, possibly due to a concentrated non-lipoprotein-related genetic effect. OSA identified linkage on chromosome 5q34 in families with higher cholesterol, possibly representing a hereditary lipoprotein phenotype. Multiple QTLs were identified, with the strongest for: total cholesterol on chromosome 5q14 (LOD 4.3); LDL on 20p12 (LOD 3.97); HDL on 3p14 (LOD 1.65); triglycerides on 18q22 (LOD 1.43); and HDL/TC ratio on 3q27-28 (LOD 2.06). Our findings suggest the presence of etiologic heterogeneity in families with early-onset CAD, potentially due to differential effects of lipoprotein phenotypes. Candidate genes are under investigation.

Resting metabolic rate and respiratory quotient: results from a genome-wide scan in the Quebec Family Study

BACKGROUND

Genes influencing resting metabolic rate (RMR) and respiratory quotient (RQ) represent candidate genes for obesity, type 2 diabetes, and the metabolic syndrome because of the involvement of these traits in energy balance and substrate oxidation.

OBJECTIVE

We conducted a genome-wide scan for quantitative trait loci (QTL) contributing to the variability in RMR and RQ.

DESIGN

Regression-based and variance components-based genome-wide autosomal scans on RMR and RQ phenotypes, obtained from indirect calorimetry, were performed in 169 families ascertained via an obese proband or from the general population.

RESULTS

We found evidence for linkage to RMR on chromosomes 3q26.1 (lod = 2.74), 1q21.2 (2.44), and 22q12.3 (1.33). QTL influencing RQ were found on chromosomes 12q13 (1.65) and 14q22 (1.83) when the analyses were performed in all families. Considerable locus heterogeneity within this population was suggested because most of the families were unlinked to any one quantitative trait locus. Significant associations between traits and linked microsatellites were detected within the linked, informative subsets.

CONCLUSIONS

We found several new QTL for energy metabolism, but the QTL on 1q may be a replication of the one reported in Pima Indians. All 3 RMR linkages overlapped regions previously linked to the metabolic syndrome or its components, and the significant association between RMR and the metabolic syndrome in the present cohort reinforces this relation. We conclude that considerable locus heterogeneity exists even within populations, which should be taken into account when considering candidate gene studies of energy metabolism phenotypes and other complex traits.

Haplotype analyses of the APOA5 gene in patients with familial combined hyperlipidemia

BACKGROUND

Familial combined hyperlipidemia (FCH) is the most common genetic lipid disorder with an undefined genetic etiology. Apolipoprotein A5 gene (APOA5) variants were previously shown to contribute to FCH. The aim of the present study was to evaluate the association of APOA5 variants with FCH and its related phenotypes in Dutch FCH patients. Furthermore, the effects of variants in the APOA5 gene on carotid intima-media thickness (IMT) and cardiovascular disease (CVD) were examined.

MATERIALS AND METHODS

The study population consisted of 36 Dutch families, including 157 FCH patients. Two polymorphisms in the APOA5 gene (-1131T>C and S19W) were genotyped.

RESULTS

Haplotype analysis of APOA5 showed an association with FCH (p=0.029), total cholesterol (p=0.031), triglycerides (p<0.001), apolipoprotein B (p=0.011), HDL-cholesterol (p=0.013), small dense LDL (p=0.010) and remnant-like particle cholesterol (p=0.001). Compared to S19 homozygotes, 19W carriers had an increased risk of FCH (OR=1.6 [1.0-2.6]; p=0.026) and a more atherogenic lipid profile, reflected by higher triglyceride (+22%) and apolipoprotein B levels (+5%), decreased HDL-cholesterol levels (-7%) and an increased prevalence of small dense LDL (16% vs. 26%). In carriers of the -1131C allele, small dense LDL was more prevalent than in -1131T homozygotes (29% vs. 16%). No association of the APOA5 gene with IMT and CVD was evident.

CONCLUSION

In Dutch FCH families, variants in the APOA5 gene are associated with FCH and an atherogenic lipid profile.

The involvement of upstream stimulatory factor 1 in Dutch patients with familial combined hyperlipidemia

Recently, the upstream stimulatory factor 1 gene (USF1) was proposed as a candidate gene for familial combined hyperlipidemia (FCH). In this study, we examined the previously identified risk haplotype of USF1 with respect to FCH and its related phenotypes in 36 Dutch FCH families. The diagnosis of FCH was based on both the traditional diagnostic criteria and a nomogram. The two polymorphisms, USF1s1 and USF1s2, were in complete linkage disequilibrium. No association was found for the individual single nucleotide polymorphisms (SNPs) with FCH defined by the nomogram (USF1s1, P = 0.53; USF1s2, P = 0.53), whereas suggestive associations were found when using the traditional diagnostic criteria for FCH (USF1s1, P = 0.08; USF1s2, P = 0.07). USF1 was associated with total cholesterol (USF1s1, P = 0.05; USF1s2, P = 0.04) and apolipoprotein B (USF1s1, P = 0.06; USF1s2, P = 0.04). Small dense LDL showed a suggestive association (USF1s1, P = 0.10; USF1s2, P = 0.09). The results from the haplotype analyses supported the results obtained for the individual SNPs. In conclusion, the previously identified risk haplotype of USF1 showed a suggestive association with FCH and contributed to the related lipid traits in our Dutch FCH families.

Variation within the gene encoding the upstream stimulatory factor 1 does not influence susceptibility to type 2 diabetes in samples from populations with replicated evidence of linkage to chromosome 1q

The gene encoding the transcription factor upstream stimulatory factor (USF)1 influences susceptibility to familial combined hyperlipidemia (FCHL) and triglyceride levels. Phenotypic overlap between FCHL and type 2 diabetes makes USF1 a compelling positional candidate for the widely replicated type 2 diabetes linkage signal on chromosome 1q. We typed 22 variants in the F11R/USF1 region (1 per 3 kb), including those previously implicated in FCHL-susceptibility (or proxies thereof) in 3,726 samples preferentially enriched for 1q linkage. We also examined glucose- and lipid-related continuous traits in an overlapping set of 1,215 subjects of European descent. There was no convincing evidence for association with type 2 diabetes in any of seven case-control comparisons, individually or combined. Family-based association analyses in 832 Pima subjects were similarly negative. At rs3737787 (the variant most strongly associated with FCHL), the combined odds ratio, per copy of the rarer A-allele, was 1.10 (95% CI 0.97-1.24, P = 0.13). In 124 Utah subjects, rs3737787 was significantly associated (P = 0.002) with triglyceride levels, but direction of this association was opposite to previous reports, and there was no corroboration in three other samples. These data exclude USF1 as a major contributor to type 2 diabetes susceptibility and the basis for the chromosome 1q linkage. They reveal only limited evidence for replication of USF1 effects on continuous metabolic traits.

Characterization of Cq3, a quantitative trait locus that controls plasma cholesterol and phospholipid levels in mice

Cq3 was identified in C57BL/6J (B6) x KK-Ay F2 mice as a quantitative trait locus (QTL) that controls plasma cholesterol and phospholipid levels, and normolipidemic B6 allele was associated with increased lipids. Cq3 was statistically significant in F2-a/a, but not in F2-Ay/a; probably because the Cq3 effect was obscured by introduction of the Ay allele, which in itself has a strong hyperlipidemic effect. Because the peak LOD score for Cq3 was identified near D3Mit102 (49.7 cM) on chromosome 3, linkage analyses with microsatellite markers located at 49.7 cM were performed in KK x RR F2, B6 x RR F2, and KK x CF1 F2. However, even a suggestive QTL was not identified in any of the three F2. By testing all pairs of marker loci, I found a significant interaction between Cq3 and the Apoa2 locus, and F2 mice with the Apoa2(KK)/Apoa2(KK); D3Mit102(B6)/D3Mit102(B6) genotype had significantly higher cholesterol levels than did F2 mice with other genotypes. The results showed that the ;round-robin' strategy was not always applicable to the search for QTL genes; probably because specific gene-to-gene interaction limited the validity of the strategy to the utmost extent.

Trait components provide tools to dissect the genetic susceptibility of migraine

The commonly used "end diagnosis" phenotype that is adopted in linkage and association studies of complex traits is likely to represent an oversimplified model of the genetic background of a disease. This is also likely to be the case for common types of migraine, for which no convincingly associated genetic variants have been reported. In headache disorders, most genetic studies have used end diagnoses of the International Headache Society (IHS) classification as phenotypes. Here, we introduce an alternative strategy; we use trait components--individual clinical symptoms of migraine--to determine affection status in genomewide linkage analyses of migraine-affected families. We identified linkage between several traits and markers on chromosome 4q24 (highest LOD score under locus heterogeneity [HLOD] 4.52), a locus we previously reported to be linked to the end diagnosis migraine with aura. The pulsation trait identified a novel locus on 17p13 (HLOD 4.65). Additionally, a trait combination phenotype (IHS full criteria) revealed a locus on 18q12 (HLOD 3.29), and the age at onset trait revealed a locus on 4q28 (HLOD 2.99). Furthermore, suggestive or nearly suggestive evidence of linkage to four additional loci was observed with the traits phonophobia (10q22) and aggravation by physical exercise (12q21, 15q14, and Xp21), and, interestingly, these loci have been linked to migraine in previous studies. Our findings suggest that the use of symptom components of migraine instead of the end diagnosis provides a useful tool in stratifying the sample for genetic studies.

Common hepatic nuclear factor-4alpha variants are associated with high serum lipid levels and the metabolic syndrome

Hepatic nuclear factor-4alpha (HNF-4alpha), a transcription factor involved in the regulation of serum lipid and glucose levels, has recently been associated with type 2 diabetes. The HNF-4alpha gene (HNF4A) resides on chromosome 20q12-q13.1, which, in addition to type 2 diabetes, has also previously been linked to high triglycerides in Finnish familial combined hyperlipidemia (FCHL) families. FCHL, characterized by elevated levels of serum total cholesterol, triglycerides, or both, is a common dyslipidemia observed in up to 20% of patients with premature coronary heart disease. Considering the clear phenotypic overlap between type 2 diabetes and FCHL, both predisposing to high serum triglycerides and glucose intolerance, we tested this gene for association in dyslipidemic families originating from two distinct populations, Finnish and Mexican, and comprising 1,447 subjects. Our data show that common HNF4A variants and haplotypes are associated with elevated serum lipid levels and the metabolic syndrome (P = 0.008-0.04), as well as with elevated glucose parameters (P = 0.008-0.03), using family-based association analysis. Importantly, both Finnish and Mexican families shared two common lipid-associated HNF4A haplotypes (P = 0.005 for total cholesterol and 0.006 for triglycerides). In conclusion, we show for the first time that common HNF4A variants are associated with high serum lipid levels and the metabolic syndrome.

Genetics of familial combined hyperlipidemia

PURPOSE OF REVIEW

To provide an overview of recent advances that have defined the first putative genes behind familial combined hyperlipidemia, the most common genetic dyslipidemia and a major risk factor for early coronary heart disease.

RECENT FINDINGS

The first locus for familial combined hyperlipidemia on 1q21-23 revealed a gene encoding a transcription factor critical in lipid and glucose metabolism, USF1. All the associated variants represent noncoding single nucleotide polymorphisms, one of which affects the binding site of nuclear proteins with a putative effect on transcript levels of USF1. Transcript analyses of fat biopsies have exposed risk-allele related changes in the downstream genes. Another recent clue to the molecular pathogenesis of familial combined hyperlipidemia is the association of the high triglyceride trait with the APOA5 gene, located on 11q. More familial combined hyperlipidemia genes are expected to be found, since linkage evidence exists for additional loci on 16q24 and 20q12-q13.1.

SUMMARY

Genetic research of familial combined hyperlipidemia families has revealed several linked loci guiding to susceptibility genes. The USF1 transcription factor is the major gene underlying the 1q21-23 linkage. Modifying genes, especially influencing the high triglyceride trait, include APOC3 and APOA5, the latter representing a downstream target of USF1 and implying a USF1-dependent pathway in the molecular pathogenesis of dyslipidemias.

A genome scan for loci influencing levels and trends of lipoprotein lipid-related traits since childhood: The Bogalusa Heart Study

Coronary heart disease is the result of life-long processes. Previous genetic linkage analyses of lipid and lipoprotein variables that can be measured throughout life have focused on a single measure at one point in time. Genome-wide linkage analyses were performed in the present study to identify loci influencing the long-term levels and trends of high-density lipoprotein cholesterol (HDLC) and low-density lipoprotein cholesterol (LDLC) and triglycerides in a longitudinal cohort. Microsatellite markers (n=357) were typed on 779 white and 444 black siblings, ages 14-43 years. Subjects had been examined serially 2-13 times with 6963 serial observations over an average of 22 years from childhood to adulthood. Total and incremental area under the growth curves of lipid traits was calculated and used as measures for long-term levels and trends. After adjusting for age, sex and body mass index, heritability estimates of total area values for all lipid variables were higher than those of a single measurement in either childhood or adulthood. In blacks, significant linkage to LDLC incremental area (peak LOD=3.6 at 50 cM) was observed on chromosome 1; and suggestive linkage for total area of LDLC (LOD=2.9 at 21 cM) on chromosome 19. Only one suggestive linkage (LOD=2.2 at 161 cM) on chromosome 2 was identified in whites for LDLC incremental area. Other suggestive linkage (LOD> or =2.0) was noted for LDLC and HDLC in terms of either total or incremental area on chromosomes 2, 5, 7 and 15 for blacks and whites. Several lipid-related candidate genes such as low-density lipoprotein receptor (LDLR), LDL receptor-related proteins 3 and 8, ApoE, ApoAII and ApoCII are located in these regions. Linkage evidence found in this community-based study indicates that regions on these chromosomes harbor genetic loci that affect the propensity to develop dyslipidemia from childhood.

A quantitative trait locus (QTL) on chromosome 6q influences birth weight in two independent family studies

Low birth weight is an important cause of infant mortality and morbidity worldwide. Birth weight has been shown to be inversely correlated with adult complex diseases such as obesity, type-2 diabetes and cardiovascular disease. However, little is known about the genetic factors influencing variation in birth weight and its association with diseases that occur in later life. We, therefore, have performed a genome-wide search to identify genes that influence birth weight in Mexican-Americans using the data from the San Antonio Family Birth Weight Study participants (n=840). Heritability of birth weight was estimated as 72.0+/-8.4% (P<0.0001) after adjusting for the effects of sex and term. Multipoint linkage analysis yielded the strongest evidence for linkage of birth weight (LOD=3.7) between the markers D6S1053 and D6S1031 on chromosome 6q. This finding has been replicated (LOD=2.3) in an independent European-American population. Together, these findings provide substantial evidence (LOD(adj)=4.3) for a major locus influencing variation in birth weight. This region harbors positional candidate genes such as chorionic gonadotropin, alpha chain; collagen, type XIX, alpha-1; and protein-tyrosine phosphatase, type 4A, 1 that may play a role in fetal growth and development. In addition, potential evidence for linkage (LOD>or=1.2) was found on chromosomes 1q, 2q, 3q, 4q, 9p, 19p and 19q with LODs ranging from 1.3 to 2.7. Thus, we have found strong evidence for a major gene on chromosome 6q that influences variation in birth weight in both Mexican- and European-Americans.

Familial combined hyperlipidemia: upstream transcription factor 1 and beyond

PURPOSE OF REVIEW

Familial combined hyperlipidemia is a common complex disease that accounts for up to 20% of premature coronary heart disease. The upstream transcription factor 1, located on 1q21, was recently shown to be linked and associated with familial combined hyperlipidemia in Finnish families. Upstream transcription factor 1 is the first gene identified by positional cloning for familial combined hyperlipidemia. Replication studies are critical to investigation of complex diseases because only they can verify the importance of the original findings. We review recent studies that examine the genetic contribution and functional consequence of upstream transcription factor 1 variants to familial combined hyperlipidemia and type 2 diabetes mellitus. Aiming beyond upstream transcription factor 1, we also evaluate novel strategies that have made it possible to globally examine the genome and the transcriptome.

RECENT FINDINGS

Three independent studies support the role of upstream transcription factor 1 in familial combined hyperlipidemia. The results for type 2 diabetes mellitus and the metabolic syndrome have been less conclusive highlight novel strategies for gene identification in familial combined hyperlipidemia.

SUMMARY

Currently, genetic and functional evidence is supportive of a role for upstream transcription factor 1 in the etiology of familial combined hyperlipidemia and its component traits, although the mechanism of causality still remains largely unknown.