HYPERCHOLESTEROLAEMIA

Hypercholesterolaemia, with little or no elevation of plasma triglycerides, is almost always due to raised plama LDL levels. Familial hypercholesterolaemia is due to deficiency of LDL receptors or to internalisation defects and may be a single gene or multigene defect. In the monogenic type, homozygotes for the abnormal gene have very high plasma cholesterol; the plasma cholesterol levels or family members of afflicted individuals show the characteristic trimodal distribution, with three distinct peaks of expression for the homozygotes with either the normal or the abnormal gene and the heterozygotes. In polygenic familial hypercholesterolaemia, the cholesterol values would show a continuous distribution, reflecting the variable expression of several gene abnormalities. The hypercholesterolaemia in the latter group is usually moderate. The main causes of secondary hypercholesterolaemia which has a higher prevalence than primary or familial hypercholesterolaemia are hypothyroidism, diabetes mellitus, nephrotic syndrome, cholestatic liver diseases, and Cushing's syndrome. Treatment of the underlying disorder normally corrects the cholesterol abnormality.