β2-glycoprotein I deficiency:: prevalence, genetic background and effects on plasma lipoprotein metabolism and hemostasis

β2-glycoprotein I (β2-GPI=apolipoprotein H) is an important autoantigen in patients with the antiphospholipid syndrome. It also plays a role in lipoprotein metabolism, such as anti-atherogenic property, triglyceride removal, and enhancement of lipoprotein lipase. Serum β2-GPI concentration of 812 apparently healthy Japanese individuals was measured by sandwich EIA. Two families with complete β2-GPI deficiency were identified. In one family, all affected had increased serum LDL-cholesterol levels or smaller particle sizes of LDL, while the other had no apparent abnormality in lipid metabolism. Individuals investigated had no history of thrombosis or overt abnormalities in hemostatic tests. A thymine corresponding to position 379 of the β2-GPI cDNA was deleted in every β2-GPI deficient individual. The incidence of this heterozygous deficiency determined by RFLP was 6.3% in Japanese and none in Caucasians. Heterozygotes had significantly lower concentrations of serum β2-GPI than did those without the mutation, yet no significantly different lipid profiles, such as total cholesterol, triglyceride, HDL-cholesterol, LDL-cholesterol, apoA-I, apoB and Lp(a), were observed. A low concentration of β2-GPI seemed not to be associated with apparent abnormality in lipoprotein metabolism.