Human KCNQ1 S140G mutation is associated with atrioventricular blocks.

BACKGROUND: We recently reported that an S140G mutation in human KCNQ1, an alpha subunit of potassium channels, was involved in the pathogenesis of familial atrial fibrillation (AF), but it is not clear whether the mutation is associated with other cardiac arrhythmias. OBJECTIVE: The purpose of this study was to further explore the association of the KCNQ1 S140G mutation with cardiac arrhythmias. METHODS: We produced a transgenic mouse model with myocardium-specific expression of the human KCNQ1 S140G mutation under the control of an alpha-cardiac myosin heavy chain promoter by standard transgenic procedure and evaluated the relationship between the KCNQ1 mutation and its phenotypes in a human family. RESULTS: Four lines of transgenic mice were established with a high level of human KCNQ1 S140G expression in the heart. Frequent episodes of first-, second-, advanced-, or third-degree atrioventricular block (AVB) occurred in at least 65% of transgenic descendants from the four lines. However, none of the five wild-type transgenic lines presented with AVBs. HMR1556, a KCNQ1-specific blocker, can terminate the AVBs. With the exception of at most three AF individuals, at least 13 AF patients were found to show obviously slow ventricular response, which may be one manifestation of AVBs. Interestingly, AF was not detected in these transgenic mice. CONCLUSION: The results suggest that human KCNQ1 S140G is also likely to be a causative mutation responsible for AVBs. The transgenic mouse model is a potential tool to explore mechanisms of AVBs.

Mapping a novel locus for familial atrial fibrillation on chromosome 10p11-q21.

BACKGROUND: Atrial Fibrillation (AF), the most common cardiac arrhythmia, is a significant public health problem in the United States, affecting approximately 2.2 million Americans. Recently, several chromosomal loci and genes have been found to be associated with familial AF. However, in most other AF cases, the genetic basis is still poorly understood. OBJECTIVE: The purpose of this study was to investigate the molecular basis of familial AF in a Dutch kindred group. METHODS: We analyzed a four-generation Dutch family in which AF segregated as an autosomal dominant trait. After the exclusion of linkage to 10q22-24, 6q14-16, 5p13, KCNQ1, KCNE2, KCNJ2 and some ion-channel-associated candidate genes, a genome-wide linkage scan using 398 microsatellite markers was performed. RESULTS: Two-point logarithms of odds (LOD) scores >1 at recombination fraction [theta] = 0.00 and a haplotype segregating with the disorder were demonstrated only across regions of chromosome 10. Subsequent fine mapping gave a maximum two-point LOD score of 4.1982 at D10S568 at [theta] = 0.00. Distinct recombination in several individuals narrowed the shared region among all affected individuals to 16.4 cM on the Genethon map (flanking markers: D10S578 and D10S1652), which corresponds to chromosome 10p11-q21. Thirteen candidate genes residing in this region, which could be associated with AF, were screened. No mutation has been found in their coding regions including the intron splice regions. CONCLUSION: We identify a novel locus for AF on chromosome 10p11-q21, which provides further evidence of genetic heterogeneity in this arrhythmia.

Up-regulation of CD36/FAT in preadipocytes in familial combined hyperlipidemia.

Familial combined hyperlipidemia (FCHL) shows many features of the metabolic syndrome. The strong genetic component makes it an excellent model to study the genetic background of metabolic syndrome and insulin resistance. Adipose tissue is believed to contribute to, or even underlie, the FCHL phenotype and is an interesting target tissue for gene expression studies. However, interpretation of adipose tissue gene expression experiments is complex since expression differences cannot only arise as a direct consequence of a genetic trait, but may also reflect an adaptation to metabolic influences at the cellular level. In the present study, we measured gene expression levels in cultured primary human preadipocytes from FCHL and control subjects. Since isolated preadipocytes were allowed to replicate for weeks under standardized conditions, the contribution of previous metabolic influences is rather small whereas genetic defects are preserved and expressed in vitro. The main finding was up-regulation of CD36/FAT in FCHL preadipocytes, confirmed in two independent groups of subjects, and a concomitant increase in CD36/FAT-mediated fatty acid uptake. CD36/FAT overexpression has previously been shown to be associated with other insulin-resistant states. The present data suggest that CD36/FAT overexpression in FCHL occurs very early in adipocyte differentiation and may be of genetic origin.

Variants in the PPARgamma gene affect fatty acid and glycerol metabolism in familial combined hyperlipidemia.

Familial combined hyperlipidemia (FCHL) is a common genetic lipid disorder characterized by premature coronary artery disease, dyslipidemia, insulin resistance, and impaired adipose tissue free fatty acid (FFA) metabolism. Increased adipose tissue FFA flux towards the liver may, in part, contribute to reduced insulin sensitivity and hyperlipidemia in FCHL. It was the objective of the present study to evaluate the contribution of the peroxisome proliferator-activated receptor gamma (PPARgamma) gene to FCHL traits related to adipocyte lipid metabolism, dyslipidemia, and insulin resistance. In a case-control panel consisting of 79 FCHL probands and 124 spouse controls, polymorphic marker D3S1259 and three intragenic PPARgamma variants, i.e., 161C > T, Pro12Ala, and Pro115Gln, were studied. The Pro115Gln variant was not found in any of the subjects. Allele frequencies of the 161C > T, Pro12Ala variants, and D3S1259 did not differ significantly between FCHL probands and spouses. In FCHL probands, individuals heterozygous or homozygous for the 161T allele had lower plasma concentrations of FFA (P < 0.05) and glycerol (P < 0.01). No significant associations were found in spouses. These findings identify PPARgamma as a quantitative trait locus for FFA and glycerol, against a background of insulin resistance for adipose tissue lipid metabolism, and therefore as a modifier gene in FCHL.

Identification of the PPARA locus on chromosome 22q13.3 as a modifier gene in familial combined hyperlipidemia.

Familial combined hyperlipidemia (FCHL) is a common genetic lipid disorder that is present in 10% of patients with premature coronary artery disease (CAD). It was the objective of the present study to evaluate the possible involvement of the PPARA locus in the pathophysiology of FCHL. Mutation detection analyses of the six coding PPARA exons resulted in the identification of four novel variants, [C/T] intron 3, S234G, [G/A] intron 5, and [C/A] 3(') UTR in three FCHL probands, whereas no novel variants were identified in spouses. In a case-control study, markers D22S275 and D22S928 were shown not to be associated with FCHL. However, D22S928, mapped within 1Mb of the PPARA gene, was shown to have a modifying effect on plasma apoCIII concentrations (P=0.011) and the combined hyperlipidemic FCHL phenotype (P=0.038). In addition two PPARA polymorphisms in intron 2 and 7 were studied, but these were not associated with FCHL. The frequency of the L162V variant was less in FCHL probands (1.98%) compared to that in spouses (4.84%). These results clearly demonstrate the genetically complex nature of FCHL and identify the PPARA gene as a modifier of the FCHL phenotype.

Identification of differentially expressed genes in subcutaneous adipose tissue from subjects with familial combined hyperlipidemia.

Subjects with familial combined hyperlipidemia (FCHL) are characterized by a complex metabolic phenotype with hyperlipidemia, insulin resistance, and central obesity. FCHL is due to impaired adipose tissue function superimposed on hepatic overproduction of lipoproteins. We investigated adipose tissue as an interesting target tissue for differential gene expression in FCHL. Human cDNA expression array analyses, in which adipose tissue from five FCHL patients was compared with that from four age, gender, and BMI matched controls, resulted in the identification of 22 up-regulated and three down-regulated genes. The genes differentially expressed imply activation of the adipocyte cell cycle genes. Furthermore, the differential expression of the genes coding for tumor necrosis factor alpha, interleukin 6, and intracellular adhesion molecule 1 support a role for adipose tissue in insulin resistance in FCHL subjects. The observed changes represent a primary genetic defect, an adaptive response, or a contribution of both.