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 5 0.53; USF1s2, P 5 0.53), whereas suggestive associations were found when using the traditional diagnostic criteria for FCH (USF1s1, P 5 0.08; USF1s2, P 5 0.07). USF1 was associated with total cholesterol (USF1s1, P 5 0.05; USF1s2, P 5 0.04) and apolipoprotein B (USF1s1, P 5 0.06; USF1s2, P 5 0.04). Small dense LDL showed a suggestive association (USF1s1, P 5 0.10; USF1s2, P 5 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.-

Objective: Familial combined hyperlipidemia (FCH) is characterized by elevated levels of total cholesterol (TC), triglycerides (TG) and apolipoprotein B (apo B) and is associated with premature cardiovascular disease (CVD). Other features of FCH are obesity and insulin resistance. Serum leptin levels have also been associated with obesity, insulin resistance and atherosclerosis. Leptin exerts its effect through the leptin receptor (LEPR). The aim of this study is to determine whether the Gln223Arg polymorphism in the LEPR gene contributes to FCH and its associated phenotypes. Methods: The study population consists of 37 families, comprising 644 subjects, of whom 158 subjects were diagnosed as FCH. The FCH diagnosis was based on plasma TC and TG levels, adjusted for age and gender, and absolute apo B levels, according to our recently published nomogram. The Gln223Arg polymorphism was studied by restriction fragment length polymorphism-PCR. Results: Carriers of one or two Arg alleles had an increased risk of FCH, compared to subjects homozygous for the Gln allele (OR ¼ 1.6 [95% CI 1.0-2.4]). A difference in high-density lipoprotein cholesterol (HDL-c) levels was present between carriers and non-carriers of an Arg allele, 1.21 vs 1.28 mmol/l, respectively (P ¼ 0.04), but no differences in obesity, insulin resistance and other lipid parameters were found. Conclusion: The Gln223Arg polymorphism in the LEPR gene is associated with FCH, which is supported by a significant association between HDL-c levels and the LEPR gene.

Patients with FCH have 2-fold elevated plasma RLP-C levels, which add to the atherogenic lipid profile and contribute to the increased risk for CVD. However, for clinical practice, non-high-density lipoprotein cholesterol is the best predictor of prevalent CVD.

To cite this article: Vermeulen SHHM, van der Vleuten GM, de Graaf J, Hermus AR, Blom HJ, Stalenhoef AFH, den Heijer M. A genome-wide linkage scan for homocysteine levels suggests three regions of interest. J Thromb Haemost 2006; 4: 1303-7.Summary. Background: An elevated plasma total homocysteine (tHcy) level is a risk factor for many clinical conditions, including vascular disease and venous thrombosis. The tHcy levels are partly determined by genetic factors. Extensive candidate gene studies have identified several genetic variants, including the MTHFR 677C>T, that influence tHcy levels, but so far only part of the genetic variation in tHcy can be explained. Objective: In order to identify chromosomal regions that influence tHcy levels, a genome-wide linkage analysis was conducted. Patients/methods: Our study population consisted of 13 pedigrees and 469 subjects with data on fasting plasma tHcy levels. A set of 377 markers covering the genome was genotyped in 275 subjects. The variance component linkage method (SOLAR version 2.1.3) was used for the two-point and multipoint linkage analyses. Results: The heritability of the age-and sexadjusted homocysteine levels was 44%. The multipoint linkage analysis identified one region with suggestive linkage on chromosome 16q (LOD score 1.76; nominal P ¼ 0.0024). Weaker evidence of linkage was found for regions on chromosome 12q (LOD score 1.57; nominal P ¼ 0.0036) and chromosome 13q (LOD score 1.52; nominal P ¼ 0.0041). Conclusions: In our families the plasma tHcy level was highly heritable. The multipoint linkage analysis identified three regions that showed weak to suggestive linkage to tHcy levels.

Familial combined hyperlipidemia (FCH), characterized by multiple lipoprotein phenotypes, is the most common hereditary lipid disorder in humans. A mutant mouse strain, HcB-19, with similar biochemical features as FCH patients, has recently been identified. The mutation causing the FCH phenotype in these mice is located in the thioredoxin interacting protein (TXNIP) gene. The TXNIP gene in mice is located on chromosome 3F2.2, which is syntenic to chromosome 1q21 in humans, a region where several groups have positioned a locus for FCH. To evaluate the potential role of TXNIP in the FCH phenotype in humans, we analyzed the coding region, 5' UTR and introns of the TXNIP gene by direct sequencing in 10 well-defined patients with FCH and 5 healthy controls. We did not find any sequence variants in these regions of the TXNIP gene in patients with FCH. Our results suggest that different genes are involved in the FCH phenotype in humans compared to mice. We conclude that in our Dutch FCH patients, the TXNIP gene, based on its intronic, exonic, and 5' UTR sequences, is not involved as a major contributor to the FCH phenotype. This article contains supplementary material, which may be viewed at the American Journal of Medical Genetics website at http://www.interscience.wiley.com/jpages/0148-7299/suppmat/index.html.