Jakob Ek

Mutation analysis of peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1) and relationships of identified amino acid polymorphisms to Type II diabetes mellitus

Abstract.Aim/hypothesis: This study aimed to investigate if variability in the peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1) gene is associated with Type II (non-insulin-dependent) diabetes mellitus. Methods: The PGC-1 gene was examined in 53 Type II diabetic patients applying single strand conformational polymorphism analysis followed by nucleotide sequencing. Identified variants were genotyped in an association study comprising 483 Type II diabetic patients and 216 glucose-tolerant control subjects. A replication study was done in an additional 201 Type II diabetic patients and 293 glucose-tolerant subjects. Furthermore, a potential interaction between the Pro12Ala polymorphism of PPAR-γ2 and the PGC-1 Gly482Ser variant on risk of Type II diabetes was investigated. Results: A total of seven variants (Ser74Leu, IVS2 + 52C→A, Thr394Thr, Asp475Asp, Gly482Ser, Thr528Thr, and Thr612Met) were identified and investigated in an association study. Six of the variants showed no association with Type II diabetes in the initial study. However, the Gly482Ser polymorphism, was more frequent among Type II diabetic patients (37.0 %) than among glucose-tolerant subjects (30.8 %) (p = 0.032). In a replication study the difference in allele frequencies of the Gly482Ser variant remained significant (p = 0.0135). The combined study yielded an allele frequency of 37.3 % (34.7–39.9) for Type II diabetic patients and 30.5 % (27.7–33.4) for glucose-tolerant subjects (p = 0.0007). No interaction between this variant and the Pro12Ala polymorphism of PPAR-γ2 was observed. Conclusion/interpretation: A widespread Gly482Ser polymorphism of PGC-1 is associated with a 1.34 genotype relative risk of Type II diabetes. [Diabetologia (2001) 44: 2220–2226]

Homozygosity of the Pro12Ala variant of the peroxisome proliferation-activated receptor-gamma2 (PPAR-gamma2): divergent modulating effects on body mass index in obese and lean Caucasian men

Aims/hypothesis. The objectives of the present investigation were to examine: 1) whether a Pro115Gln variant in the peroxisome proliferator-activated receptor-γ2 (PPAR-γ2) is associated with juvenile-onset obesity among Danish Caucasianmen and 2) whether the relation of a Pro12Ala polymorphism in PPAR-γ2 with BMI and long-term weight regulation differ between lean and obese subjects within the same cohort. Methods. The Pro115Gln and Pro112Ala variants were examined using PCR and RFLP in a group of 752 subjects with a Body Mass Index (BMI) of 31.0 kg/m2 or more and in 869 non-obese control subjects. Results. We did not find Pro115Gln in any of the 1621 male subjects we examined. Among the males with juvenile-onset obesity, the allelic frequency of the Pro12Ala polymorphism was 14 % (95 % confidence interval: 12–16 %) compared with 16 % (14–17 %) among the non-obese control subjects (NS). Heterozygosity of the codon 12 variant was not associated with differences in BMI or changes in body weight regulation during follow up in lean or obese subjects. In the group of obese subjects, 21 homozygous Ala12Ala carriers had, however, a higher BMI (38.9 ± 5.4 kg/m2 (means ± SD) vs 35.5 ± 5.5 kg/m2, p = 0.008) and a higher weight gain (0.27 ± 0.24 kg · m–2· year–1 vs 0.10 ± 0.24 kg · m–2· year–1, p = 0.004), compared with wild-type carriers. Moreover, within the control group of 869 men the 14 homozygous carriers of the variant had a lower BMI (24.4 ± 2.7 kg/m2 vs 26.2 ± 3.7 kg/m2, p = 0.005) and a slower increase in BMI (0.11 ± 0.11 kg · m–2· year–1 vs 0.17 ± 0.11 kg · m–2· year–1, p = 0.002) compared with wild-type carriers. Conclusion/interpretation. The codon 12 variant of PPAR-γ2 is not intrinsically associated with juvenile obesity. The variant may in its homozygous form interact, however, with various combinations of genetic and environmental factors in lean and obese subjects to cause divergent modulating effects on BMI and long-term body weight control. [Diabetologia (1999) 42: 892–895]

Studies of the Pro12Ala polymorphism of the peroxisome proliferator-activated receptor-γ2 (PPAR-γ2) gene in relation to insulin sensitivity among glucose tolerant Caucasians

Abstract.Aims/hypothesis: We examined whether the Pro12-Ala polymorphism of the human peroxisome proliferator-activated receptor-γ2 (PPAR-γ2) gene was related to altered insulin sensitivity among glucose-tolerant subjects or a lower accumulated incidence or prevalence of IGT and Type II (non-insulin-dependent) diabetes mellitus among Scandinavian Caucasians. Methods: The Pro12Ala polymorphism was examined using PCR-RFLP. Whole-body insulin sensitivity measured under hyperinsulinaemic-euglycaemic conditions was estimated in a population-based sample of 616 glucose tolerant Swedish Caucasian men at age 70. In addition, insulin sensitivity index was measured using IVGTT and Bergman minimal modelling in a population-based sample of 364 young healthy Danish Caucasians. Finally, we evaluated whether the polymorphism predicted Type II diabetes and IGT in 841 seventy-year-old Swedish men. A case-control study was carried out in 654 unrelated Danish Type II diabetic patients and 742 Danish glucose tolerant subjects matched for age and sex. Results: Whole-body insulin sensitivity was significantly improved in carriers compared with non-carriers of the Ala-allele of the codon 12 polymorphism in Swedish Caucasian men (6.0 ± 2.5 vs 5.6 ± 2.5 mg · kg–1· min–1· [mU/l]–1· 100, p = 0.044). The same tendency, but not significant, was observed in the insulin sensitivity index among the group of young healthy Danish Caucasians. The incidence of Type II diabetes and IGT among the Swedish subjects at the age of 70 was similar in the three genotype-groups of the Pro12Ala variant and the Ala-allele was not related to a lower prevalence of Type II diabetes in Danish Caucasians. Conclusion/interpretation: The Ala-allele of the PPAR-γ2 polymorphism is associated with improved whole body insulin sensitivity among Swedish Caucasians. [Diabetologia (2001) 44: 1170–1176]

Genetic evidence that HNF-1α–dependent transcriptional control of HNF-4α is essential for human pancreatic β cell function

Mutations in the genes encoding hepatocyte nuclear factor 4α (HNF-4α) and HNF-1α impair insulin secretion and cause maturity onset diabetes of the young (MODY). HNF-4α is known to be an essential positive regulator of HNF-1α. More recent data demonstrates that HNF-4α expression is dependent on HNF-1α in mouse pancreatic islets and exocrine cells. This effect is mediated by binding of HNF-1α to a tissue-specific promoter (P2) located 45.6 kb upstream from the previously characterized Hnf4α promoter (P1). Here we report that the expression of HNF-4α in human islets and exocrine cells is primarily mediated by the P2 promoter. Furthermore, we describe a G → A mutation in a conserved nucleotide position of the HNF-1α binding site of the P2 promoter, which cosegregates with MODY. The mutation results in decreased affinity for HNF-1α, and consequently in reduced HNF-1α–dependent activation. These findings provide genetic evidence that HNF-1α serves as an upstream regulator of HNF-4α and interacts directly with the P2 promoter in human pancreatic cells. Furthermore, they indicate that this regulation is essential to maintain normal pancreatic function.

Genetic epidemiology of MODY in the Czech republic: new mutations in the MODY genes HNF-4α, GCK and HNF-1α

Aims/hypothesisThe aim of this study was to examine the prevalence and nature of mutations in HNF4α/MODY1, GCK/MODY2 and HNF-1α/MODY3 genes in Czech subjects with clinical diagnosis of MODY.MethodsWe studied 61 unrelated index probands of Czech origin (28 males, 33 females) with a clinical diagnosis of MODY and 202 family members. The mean age of probands was 22.7±12.0 years (range, 6–62) and the mean age at the first recognition of hyperglycaemia was 14.7±6.0 years (range, 1–25). The promotor and coding regions inclusive intron exon boundaries of the HNF-4α, GCK and HNF-1α genes were examined by PCR-dHPLC (HNF-1α and GCK) and direct sequencing.ResultsWe identified 20 different mutations in the HNF-4α, GCK and HNF-1α in 29 families (48% of all families studied), giving a relative prevalence of 5% of MODY1, 31% of MODY2 and 11.5% of MODY3 among the Czech kindred with MODY. Three of 3, 10 of 11 and 1 of 6 of the mutations identified in HNF-4α, GCK and HNF-1α respectively, were new.Conclusion/interpretationOf the families 48% carried mutations in the MODY1–3 genes and of the identified mutations 70% were new. In 52% of Czech families with clinical characteristics of MODY, no mutations were found in the analysed genes. This finding shows that the majority of MODY mutations in a central European population are local and that other MODY genes could be responsible for autosomal dominant transmission of diabetes mellitus.

PGC-1α Gly482Ser Polymorphism Associates With Hypertension Among Danish Whites

PGC-1α is a coactivator of numerous transcription factors and is expressed in tissues with high energy demands and abundant in mitochondria. It is induced in the myocardium on fasting and physical exercise, and cardiac-specific overexpression stimulates mitochondrial biogenesis in mice. The common Gly482Ser polymorphism of PGC-1α has previously shown association with arterial hypertension among Austrian men. Thus, we aimed at investigating this relationship in the Danish white population. The Gly482Ser polymorphism was genotyped in a total of 2562 Danish white subjects using polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) and a GenoView locked nucleic acid assay (LNA), and the relationships of this variant with blood pressure levels and arterial hypertension were analyzed. Furthermore, we performed a combined analysis of the data from the present study in combination with previously published results. The Ser/Ser genotype was significantly associated with a reduced risk of hypertension and with lower systolic, diastolic, and mean arterial blood pressure levels, predominantly among women. Finally, in a combined analysis using data obtained in both sexes, the Ser/Ser genotype group had an estimated odds ratio of 0.70 (95% confidence interval, 0.56 to 0.86) for hypertension compared with Gly/X carriers (P=0.001). In conclusion, the Ser allele of PGC-1α Gly482Ser confers a significantly reduced risk of hypertension in whites. Further studies are needed to elucidate the differential role of this polymorphism in men and women.

Variation in the peroxisome proliferator-activated receptor δ gene in relation to common metabolic traits in 7,495 middle-aged white people

Aims/hypothesisStudies in animals reveal that peroxisome proliferator-activated receptor δ (PPARδ) regulates glucose metabolism and insulin sensitivity in both the liver and skeletal muscles. Moreover, PPARδ augments physical endurance and increases oxidative metabolism, thereby averting obesity. Thus, we hypothesised that common variation in the PPARD gene is associated with insulin resistance and metabolic traits.Materials and methodsWe studied variation in the exonic region of PPARD. Based upon the results of variant detection and information derived from the HapMap data resource, we selected common variants and tag single-nucleotide polymorphisms for genotyping in 7,495 white subjects, including 1,416 patients with type 2 diabetes.ResultsFourteen nucleotide variants were identified and a total of 12 variants capturing the common variation of PPARD were genotyped. In the population-based Inter99 (ClinicalTrials.gov ID no: NCT00289237) sample we observed no robust association with homeostasis model assessment of insulin resistance (HOMA-IR), adiposity measures or fasting serum lipids. Similarly, no association with type 2 diabetes or the metabolic syndrome was found.Conclusions/interpretationBased on thorough investigation, we conclude that common variation in PPARD does not significantly affect the risk of metabolic disease in the population studied. Given the confidence intervals that were found for effect size estimates, we can effectively rule out an increase in HOMA-IR of any tag SNP above 7% per allele, assuming an additive model. Likewise, we can exclude an odds ratio of type 2 diabetes above 1.27 per allele.

Mutations in the VNTR of the carboxyl-ester lipase gene (CEL) are a rare cause of monogenic diabetes.

We have previously shown that heterozygous single-base deletions in the carboxyl-ester lipase (CEL) gene cause exocrine and endocrine pancreatic dysfunction in two multigenerational families. These deletions were found in the first and fourth repeats of a variable number of tandem repeats (VNTR), which has proven challenging to sequence due to high GC-content and considerable length variation. We have therefore developed a screening method consisting of a multiplex PCR followed by fragment analysis. The method detected putative disease-causing insertions and deletions in the proximal repeats of the VNTR, and determined the VNTR-length of each allele. When blindly testing 56 members of the two families with known single-base deletions in the CEL VNTR, the method correctly assessed the mutation carriers. Screening of 241 probands from suspected maturity-onset diabetes of the young (MODY) families negative for mutations in known MODY genes (95 individuals from Denmark and 146 individuals from UK) revealed no deletions in the proximal repeats of the CEL VNTR. However, we found one Danish patient with a short, novel CEL allele containing only three VNTR repeats (normal range 7–23 in healthy controls). This allele co-segregated with diabetes or impaired glucose tolerance in the patient’s family as six of seven mutation carriers were affected. We also identified individuals who had three copies of a complete CEL VNTR. In conclusion, the CEL gene is highly polymorphic, but mutations in CEL are likely to be a rare cause of monogenic diabetes.

Identification of Novel Variants in the Hepatocyte Nuclear Factor-1α Gene in South Indian Patients with Maturity Onset Diabetes of Young

CONTEXT Mutations in the HNF 1A gene are the most common cause of maturity-onset diabetes of the young (MODY) in most populations. India currently has the largest number of people with diabetes in the world, and onset of type 2 diabetes occurs at a younger age with possible overlap with MODY. There are very few data on MODY mutations from India. OBJECTIVE The objective was to screen coding and promoter regions of HNF1A gene for mutations in unrelated South Indian subjects in whom a clinical diagnosis of MODY was made. DESIGN This was an observational cross-sectional study. SETTING The study was conducted at a diabetes specialties centre in Chennai in southern India. PATIENTS Ninety-six unrelated south Indian subjects in whom clinical diagnosis of MODY was made were included in the study. The control population comprised of 57 unrelated nondiabetic subjects selected from the Chennai Urban Rural Epidemiology Study, a study conducted on a representative population (aged > or =20 yr) of Chennai. RESULTS We identified nine novel variants comprising seven mutations (one novel mutation -538G>C at promoter region and six novel coding region mutations) and two polymorphisms in the HNF1A gene. Functional studies revealed reduced transcriptional activity of the HNF1A promoter for two promoter variants. We also observed cosegregation with diabetes of the Arg263His coding region mutation in eight members of one MODY family, whereas it was absent in nondiabetic subjects of this family. CONCLUSION This study suggests that mutations in the HNF1A gene comprise about 9% of clinically diagnosed MODY subjects in southern India and a novel Arg263His mutation cosegregates with MODY in one family.

Autosomal inheritance of diabetes in two families characterized by obesity and a novel H241Q mutation in NEUROD1.

Background:  The aim of the study was to search for mutations in the NEUROD1 and IPF‐1 genes in patients with clinical characteristics of maturity‐onset diabetes of the young (MODY) but with no mutations in the HNF‐4A (MODY1), GCK (MODY2) and TCF1 (MODY3) genes.