Novel rare alleles of ABCA1 are exclusively associated with extreme high-density lipoprotein-cholesterol levels among the Han Chinese

BACKGROUND: High-density lipoprotein (HDL) is a major plasma lipoprotein directly associated with cholesterol metabolism. The ATP binding cassette transporter 1 gene (ABCA1) is one of the major genes modulating plasma levels of HDL-cholesterol (HDL-C). Rare alleles of ABCA1 associated with extreme HDL-C concentrations have not been previously investigated in the Chinese. METHODS: Blood samples were collected from 470 subjects whose HDL-C concentrations were within the top 5% of the distribution, 335 subjects in the lowest 5%, and 220 within the range 5%-95%. First, we sequenced all exons of the ABCA1 gene from 50 subjects from the group with extremely high HDL-C, and 50 from the group with extremely low HDL-C concentrations. Next, in the remaining subjects, we genotyped the non-synonymous variants identified exclusively with either extreme group. RESULTS: Four novel non-synonymous alleles were identified; all were rare. Alleles c.3029C>T (p.Ala1010Val) and c.5399A>G (p.Asn1800Ser) were found exclusively in the low group, c.2031C>A (p.Asp677Glu) and c.2660G>T (p.Cys887Phe) exclusively in the high group. CONCLUSIONS: Our results show that some rare alleles of ABCA1 are associated with marked phenotypes, supporting the "rare-variant common-disease" hypothesis. Certain alleles also provide tools for identifying individuals at high risk of dyslipidaemia, allowing for early therapeutic intervention.