Familial lecithin-cholesterol acyltransferase deficiency in a Japanese family: evidence for functionally defective enzyme in homozygotes and obligate heterozygotes.

Lecithin-cholesterol acyltransferase (LCAT) mass and activity were measured in a Japanese family with familial LCAT deficiency. The two LCAT-deficient subjects had LCAT mass approximately 40-46% of normal (2.65 and 2.31 micrograms/ml respectively, as compared with normal levels of 5.76 +/- 0.95 microgram/ml in 19 Japanese subjects) and enzyme activity less than 10% of normal (9.1 and 8.3 nmol/h/ml respectively, as compared with normal levels of 100 nmol/h/ml). All obligate heterozygotes examined, including the father of the two LCAT-deficient subjects, and all five children of the deficient subjects had LCAT mass approximately 72-80% of the normal LCAT mass (4.12, 4.38, 4.45, 4.48, 4.49, 4.61 micrograms/ml, respectively) and LCAT activity approximately half normal (51.9, 52.4, 54.2, 56.6, and 57.2 nmol/h/ml). We conclude that the two LCAT-deficient subjects of this family have functionally defective enzyme. Furthermore, the data suggest that the plasma of the obligate heterozygotes contain both normal and functionally defective enzymes.