Primary hyperlipidaemia.

It is estimated that over 60% of the variability in serum lipids is genetically determined, most of this variation being due to polygenic influences. Interaction between the latter and environmental factors is probably the commonest cause of hyperlipidaemia in the general population. Familial forms of hyperlipidaemia are usually more clearly defined, especially those which have a monogenic or dominant pattern of inheritance, but are less common. This type of disorder, exemplified by familial hypercholesterolaemia, is expressed independently of environmental influences. In contrast, in familial type III hyperlipoproteinaemia inheritance of the underlying gene defect is often insufficient to produce hyperlipidaemia unless additional environmental or genetic influences coexist. Rarely, hyperlipidaemia is recessively inherited, as in familial deficiency of lipoprotein lipase and of apolipoprotein CII. Primary hyperlipidaemias characterized by severe hypertriglyceridaemia predispose to acute pancreatitis whereas those disorders characterized by hypercholesterolaemia, apart from hyper alpha lipoproteinaemia, are associated with an increased risk of premature vascular disease.