Cellular cholesterol efflux in heterozygotes for tangier disease is markedly reduced and correlates with high density lipoprotein cholesterol concentration and particle size.

Tangier disease (TD), caused by mutations in the ATP-binding cassette 1 (ABC-1) gene, is a rare genetic disorder characterized by severe deficiency of high density lipoproteins (HDL) in the plasma, hypercatabolism of HDL, and defective apolipoprotein (apo)-mediated cellular cholesterol efflux. In the present study, we assessed plasma lipid concentrations, HDL particle size and subspecies, and cellular cholesterol efflux in 9 TD heterozygotes from a kindred in which the proband was homozygous for an A-->C missense mutation at nucleotide 5338 of the ABC-1 transcript. Relative to age- and gender-matched controls from the Framingham Offspring Study (FOS), TD heterozygotes had significant reductions (P < 0.000) in HDL-C (-54% female; -40% male) and apoA-I (-33% female; -37% male) concentrations, as well as significantly less cholesterol (-68% female; -58% male) distributed in the largest HDL subclasses, H5 and H4. Consequently, HDL particle size (nm) was significantly smaller (P < 0.000) in TD heterozygotes (8.6 +/- 0.6 female; 8.7 +/- 0.1 male) relative to FOS controls (9.4 +/- 0.4 female; 9.0 +/- 0.3 male). Further studies demonstrated that apoA-I-mediated cellular cholesterol efflux in TD heterozygotes was essentially half that of controls (11 +/- 2 vs. 20 +/- 3% of total [(3)H]cholesterol, P < 0. 001), with strong correlations observed between cholesterol efflux and both HDL-C level (r = 0.600) and particle size (r = 0.680). In summary, our data demonstrate that apolipoprotein-mediated cholesterol efflux is aberrant in TD heterozygotes, as it is in homozygotes. This finding, along with the associations observed between HDL-C concentration, HDL particle size, and cholesterol efflux, supports the concept that plasma HDL-C levels are regulated, in part, by cholesterol efflux, which in turn influences HDL particle size and, ultimately, HDL apoA-I catabolism.