Association of isoapolipoprotein-E3 deficiency with heterozygous familial hypercholesterolaemia: implications for lipoprotein physiology.

A prepubertal girl with both homozygous isoapolipoprotein-E3 deficiency (the genetic defect underlying type-III hyperlipoproteinaemia) and heterozygous familial hypercholesterolaemia (familial type-IIa hyperlipoproteinaemia) presented with severe hypercholesterolaemia and antecubital and popliteal planar xanthomas. She responded dramatically to clofibrate. Her mother was normolipidaemic and heterozygous for apo-E3-deficiency. Her father, an obligate apo-E3-deficient heterozygote, and his similarly affected brother died prematurely with severe hypercholesterolaemia which had been refractory to clofibrate. Her paternal grandfather, who had the same combination of disorders as the proband, also responded to clofibrate, whereas her grandmother was normolipidaemic. Hence homozygous apo-E3 deficiency may present during childhood as severe hypercholesterolaemia when combined with familial hypercholesterolaemia, suggesting that the low-density-lipoprotein receptor may represent one mechanism whereby apo-E3-deficient remnants of very-low-density lipoproteins and chylomicrons are cleared from the plasma compartment. The removal of such apo-E3-deficient remnants is especially facilitated by clofibrate.