We have studied a family carrying a variant of the class 2 mutation of familial hypercholesterolemia (FH) in which there is unusual longevity and in which obligate heterozygotes did not express constant or statistically significant hypercholesterolemia. The heterozygotes have the same kinetic defect in the processing of low density lipoprotein (LDL) receptors in their fibroblasts and the reduced fractional catabolic rate for apoLDL that is characteristic of other patients with heterozygous FH. However, their plasma lipid and lipoprotein levels are not as strikingly abnormal because they have normal or near normal rates of apoLDL synthesis.