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

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, P5 0.05; USF1s2, P5 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. — vander Vleuten,G.M. , A. Isaacs, A.Hijmans, C.M. vanDuijn, A. F. H. Stalenhoef, and J. de Graaf. The involvement of upstream stimulatory factor 1 in Dutch patients with familial combined hyperlipidemia. J. Lipid Res. 2007. 48: 193–200. Supplementary key words single nucleotide polymorphisms & mRNA expression & total cholesterol & apolipoprotein B & small dense low density lipoprotein Familial combined hyperlipidemia (FCH; Online Mendelian Inheritance in Man 144250) is the most common genetic lipid disorder of unknown cause in humans, affecting up to 5% of the general population (1). Major characteristics of FCH include increased levels of apolipoprotein B (apoB), triglycerides (TGs), and/or plasma total cholesterol (TC). Other FCH phenotypes are decreased levels of high density lipoprotein cholesterol and the presence of small, dense low density lipoprotein (sdLDL). In addition, patients with FCH have a 2-fold increased risk of cardiovascular disease (CVD) and are often obese and insulin-resistant (2). During the past few years, several groups have performed linkage analyses in an attempt to determine the genetic defects causing FCH (3–8). By doing this, a locus on chromosome 1q21-23 was identified (4, 7–9). The first candidate gene proposed in this region was the thioredoxininteractingprotein gene (TXNIP) (10). It was demonstrated, however, that TXNIP was not a major contributor to the FCH phenotype (11–13). More recently, a second candidate gene, the upstream stimulatory factor 1 gene (USF1), was suggested as the prime candidate gene for FCH in this linkage region in 60 Finnish FCH families (12). Twenty-three single nucleotide polymorphisms (SNPs) were reported in the USF1 gene. Two of these SNPs, USF1s1 (39 untranslated region; rs3737787) and USF1s2 (intron 7; rs2073658), individually and combined into a haplotype, showed linkage and association with FCH and multiple phenotypes of FCH, including TG, apoB, TC, and sdLDL, implying that USF1 contributes to the complex pathophysiology of FCH in these Finnish FCH families (12). The association of USF1 with FCH, however, was strongest in males with increased levels of TGs (12). Huertas-Vazquez et al. (5) reported that USF1 was associated with FCH and increased TG levels in 24 Mexican Manuscript received 26 April 2006 and in revised form 30 August 2006 and in re-revised form 17 October 2006. Published, JLR Papers in Press, October 25, 2006. DOI 10.1194/jlr.M600184-JLR200 Abbreviations: apoB, apolipoprotein B; CHD, coronary heart disease; CVD, cardiovascular disease; FBAT, family-based association test; FCH, familial combined hyperlipidemia; HBAT, haplotype-based association test; HOMA, homeostasis model assessment; HSL, hormonesensitive lipase; LDL-c, low density lipoprotein cholesterol; lod, log of the odds; PBAT, pedigree-based association test; PBMC, peripheral blood mononuclear cell; sdLDL, small dense low density lipoprotein; SNP, single nucleotide polymorphism; TC, total cholesterol; TG, triglyceride; TXNIP, thioredoxin-interacting protein; USF1, upstream stimulatory factor 1. To whom correspondence should be addressed. e-mail: j.degraaf@aig.umcn. nl The online version of this article (available at http://www.jlr.org) contains two additional tables. Copyright D 2007 by the American Society for Biochemistry and Molecular Biology, Inc. This article is available online at http://www.jlr. org Journal of Lipid Research Volume 48, 2007 193 This is an Open Access article under the CC BY license. FCH families, whereas other phenotypes were not investigated. No sex-specific effect of USF1 was found in these families. Coon et al. (14) investigated the association of USF1 with FCH in Utah pedigrees ascertained for early death attributable to coronary heart disease (CHD), early stroke, or early-onset hypertension. They reported suggestive associations for FCH, TG, and low density lipoprotein cholesterol (LDL-c) levels in the pedigrees ascertained for early stroke and early onset of hypertension. However, in the families ascertained for early death attributable to CHD, in which 60% of the FCH patients were present, no association of USF1 with FCH was found (14). The USF1 protein regulates the transcriptional activation of a variety of genes involved inglucose and lipidmetabolism and in the development of atherosclerosis (15, 16). USF1 plays a pivotal role in adipose tissue, where it influences de novo lipogenesis by mediating the glucose-regulated expression of hormone-sensitive lipase (HSL), a key enzyme in the regulation of lipid storage in adipose tissue (17). An interaction between SNPs in the HSL and USF1 genes in postprandial TG levels has been reported previously (18). Despite this, HSL activity in adipose tissuewas unchanged in Finnish patients with FCH (19). USF1 also influences the transcription of fatty acid synthase (FAS), which is involved in the synthesis of fatty acids (15, 20). FAS might play a role in FCH, as patients with FCH have decreased circulating levels of FAS ligand (21). USF1 also plays a role in the transcription of several apolipoproteins (APOCIII, APOAII, and APOE) (16, 22), glucokinase (23), hepatic lipase (24), angiotensinogen (25), and ABCA1 (26). Genetic variations inAPOCIII,APOAII, and hepatic lipase have been associated with FCH (27–30); however, the role of glucokinase, angiotensinogen, and ABCA1 in FCH has not been explored yet. In this study, we evaluated the putative role of the USF1 gene in Dutch FCH families. We investigated the effect of two individual SNPs, and the haplotypes formed by these two SNPs, on FCH and its associated phenotypes, including not only lipids and lipoproteins but also parameters of obesity and insulin resistance.