Abstract-The scavenger receptor class B type I (SR-BI) is a lipoprotein receptor that has been shown to be important in high density lipoprotein cholesterol (HDL-C) metabolism in mice. To determine its role in humans, we have characterized the human SR-BI gene and investigated its genetic variation in 489 white men and women. Five variants were demonstrated: 2 in introns (3 and 5) and 3 in exons (1, 8, and 11). Three variants at exons 1 and 8 and intron 5 with allele frequencies Ͼ0.1 were used to examine associations with lipid or anthropometric variables. The exon 1 variant was significantly (PϽ0.05) associated with increased HDL-C and lower low density lipoprotein cholesterol (LDL-C) values in men, but no associations were observed in women. The exon 8 variant was associated in women with lower LDL-C concentrations (3.05Ϯ0.98 mmol/L and 3.00Ϯ0.93 mmol/L for heterozygotes and homozygotes, respectively) compared with women homozygous for the common allele T he scavenger receptor class B type I (SR-BI) is a multilipoprotein receptor found in the liver and steroidogenic glands of both mice 1 and humans 2,3 (for a review, see Reference 4). The cDNA for human SR-BI (also known as CLA-1) was originally cloned by homology to human CD36 and rat LIMPII, which are members of a family of transmembrane proteins. 5 An independent expression cloning study identified the hamster homologue by its ability to mediate the binding of modified LDL, and it was also shown to bind native LDL. 6 Subsequently, murine SR-BI was shown to mediate the uptake of lipid, but not apoprotein, from HDL into cells, 1 a process described as selective uptake. [7][8][9] This finding established SR-BI as the first HDL transmembrane receptor to be identified and cloned. Further studies of the human homologue demonstrated that it also is a multilipoprotein receptor that binds HDL, LDL, and VLDL. 2,10 Further analysis in vivo in mice and rats has supported a role for SR-BI in cholesterol metabolism. Targeted disruption of apoAI, the major protein component of HDL, leads to an increase in SR-BI expression in the adrenal glands of mice, 11 where HDL-C is used for steroid hormone synthesis. In addition, SR-BI expression levels in the adrenal glands are increased in response to adrenocorticotropic hormone and decreased in response to dexamethasone. 12 Estrogen treatment at high doses in rats greatly reduces SR-BI expression in the liver while it increases SR-BI expression in the adrenal gland and ovarian corpus luteal cells. 13 Transient overexpression of SR-BI in the livers of mice by adenoviral infection leads to a marked reduction in plasma HDL levels and a concomitant increase in plasma LDL/IDL cholesterol levels. 14 Finally, targeted disruption of the SR-BI gene in mice leads to a significant increase in plasma HDL 15,16 and reduced selective uptake of cholesterol from HDL into the liver. 16 Thus, SR-BI has clearly been shown to be a very important player in HDL metabolism in mice. However, although mice have HDL as the major cholesterol-carrying lipopr...

Background: Patients with familial hypercholesterolemia (FH) have a high risk of premature cardiovascular disease (PCVD). Mutations in the LDL receptor (LDLR)gene and the R3500Q mutation in the apolipoprotein B (APOB) gene are known to cause FH, but lack of high-throughput methods makes routine genetic diagnosis difficult. The objective of this work was to develop a DNA array for large-scale identification of mutant LDLR alleles. Methods: We developed a low-density oligonucleotide microarray to identify 118 DNA sequence variations (117 for the LDLR gene and 1 for the APOB gene). We verified specificity and sensitivity by analyzing 1180 previously sequenced DNA samples, and conducted a blind study screening 407 Spanish patients with a clinical diagnosis of FH. Results: The DNA array confirmed the previous genotyping results in almost all cases. In the blind study, the microarray detected at least 1 mutation in 51% of the patients for whom clinical diagnosis was classified as certain according to Dutch FH-MEDPED criteria; it also identified mutations in 37% of those with a diagnosis of probable/possible FH, thus giving a definite diagnosis.

Mutations in the low-density lipoprotein receptor (LDLR) gene cause familial hypercholesterolemia (FH), an autosomal dominant inherited disorder associated with an increased risk of premature atherosclerosis. The aim of this study was to characterize the LDLR mutations in a group of 476 apparently non-related Spanish FH patients. The promoter region and the 18 exons with their flanking intron sequences of the LDLR gene were screened by PCR-SSCP analysis and DNA sequencing. In addition, we tested for the presence of the mutation p.R3500Q in the gene coding for apolipoprotein B-100 (apo B-100). We found 77 mutations previously described, and 39 novel mutations affecting the LDLR gene: 8 missense, 5 nonsense, 15 frameshift, 5 splicing, 4 in frame, one nucleotide change in the non-coding sequence of exon 1, and one silent variant. We have identified al least one of these LDLR gene mutations in 329 subjects (69%). Four patients were homozygous, 4 patients were compound heterozygous, 48 patients were found to carry two different sequence variants in the same allele and 4 patients carried three different sequence variants in the same allele. Additionally, 4 subjects were carriers of the p.R3500Q mutation in the apo B gene. All of these findings indicate that there is a broad spectrum of mutations and sequence variants in the LDLR gene causing FH in Spain.

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