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Deficiencies of lipoproteins occur as genetic disorders or may be presenting features of underlying disease. Familial high density lipoprotein (HDL), or alpha-lipoprotein, deficiency so far described includes Tangier disease, Lecithin: cholesterol acyltransferase (LCAT) deficiency, A-I Variants syndrome and Fish-eye disease. In 1981 Vergani described a familial aggregation of low HDL-cholesterol (less than 33 mg/dl) and Apo A (about 50% of normal levels) in the presence of normal VLDL and LDL-cholesterol. LCAT and lipoprotein lipase activities, both extrahepatic and hepatic, were normal. By zonal ultracentrifugation HDL2 subclass was found to be reduced. HDL apoproteins, examined by isoelectric focusing in polyacrylamide gel, were qualitatively normal. No disorders to which low levels of HDL might be secondary (e.g., overweight, cigarette smoking, nephropathy, liver disease) are present in the affected members. The underlying biochemical defect is unknown but probably involves altered synthesis or catabolism of HDL. Familial hypo-alpha-lipoproteinemia is accompanied by a high prevalence of premature myocardial infarction and sudden death. The genetic analysis of the disorder is consistent with autosomal inheritance. The criteria for the definition of familial hypo-alpha-lipoproteinemia are, therefore, as follows: 1) low HDL-cholesterol level in the presence of normal VLDL and LDL-cholesterol levels; 2) absence of diseases or factors to which hypo-alpha-lipoproteinemia might be secondary; 3) presence of a similar lipoprotein pattern in a first degree relative.