Very occasionally (roughly one in a million cases), an individual inherits a abnormal gene for the LDL receptor from both parents, leading to a homozygous familial hypercholesterolaemia in which there are essentially no functional LDL receptors. This situation is associated with very high levels of LDL and very accelerated atherosclerotic complications.
Recently, a genetic mutation of apo B, which also results in defective removal of LDL via the LDL-receptor pathway, has been described. The frequency of familial defective apo B is somewhat less than familial hypercholesterolaemia. The condition results in an identical clinical picture to that seen in heterozygous familial hypercholesterolaemia.
