PRIMARY HYPERLIPIDAEMIA

This is a distinct clinical entity characterised by elevated levels of total cholesterol and xanthelesma, LDL, tendonous xanthomata, corneal arteriosclerosis. arcus, and premature The mode of inheritance is monogenic, autosomal dominant. The biochemical hallmark is a defect of the LDL receptor. There is a high frequency of heterozygotes (1 in about 500 Caucasians), the homozygous form is much rarer, being present in only about 1 in a million individuals. Almost all homozygotes die of a fatal myocardial infarction before the age of 30. In heterozygotes, the disease often presents in middle life, with a mean onset at 43 years in males and 53 years in females. Their risk of developing CHD is as much as 25 times greater than that in normal individuals above the age of 30 years. The average plasma cholesterol level in heterozygotes is about 9.0 mmoVL; homozygotes have levels which are >15.0 mmoliL. Values for plassma LDL are also uniformly high and proportionate to the elevation in total cholesterol concentration. Familial combined hyperlipoproteinaemia. This familial condition, the most common of the primary hyperlipidaemias, presents as a variety of hyperlipidaemic types in affected individuals within one family and is difficult to classify. The pathophysiologic mechanisms responsible for the disease are unknown, and the exact genetic inheritance is not clear but it is believed to be a monogenic, dominant trait. Patients identified with the disorder are at an increased risk (about 3-4 times) for premature atherosclerosis. Many of these patients have hypercholesterolaemia but only rarely do their plasma total cholesterol levels exceed 10 mmol/L. Tendonous xanthomas are rarely present and hyperlipidaemia does not manifest itself until adulthood, unlike homozygotes with familial hypercholesterolaemia.