Inheritance of endogenous hypertriglyceridaemia type IIB or IV.

The genetic background of endogenous hypertriglyceridaemia was evaluated in 239 first-degree relatives of 48 probands with serum triglyceride level in excess of 30.0 mM and with either normal (type IV) or elevated (type IIB) serum cholesterol concentration. In one quarter of the families, all examined first-degree relatives of the proband were normolipidaemic and, thus, the disorder was classified as non-genetic. Nine of 26 probands with IV in contrast to only three of 22 probands with type IIB abnormality fell into this category. In 75% of the families the hyperlipoproteinaemia was caused by one or several abnormal genes. A multiple-type (combined) familial hyperlipidaemia could be demonstrated in 30 families and a single-type IIB or IV familial disease was found in 6 instances. Thus, the multiple-type hyperlipoproteinaemia seems to be responsible for the elevated serum triglyceride level in more than one-half of the cases with moderate to severe hyperglyceridaemia while a pure familial endogenous hypertriglyceridaemia is relatively rare. Exactly 50% of the members of families with the multiple-type lipid disorder were affected but the distribution of individual cholesterol and triglycerides values did not show a definite bimodality. It is possible that the abnormality is heterogeneous and includes several disease entities, which are indistinguishable by a conventional lipid or lipoprotein analysis but can be separated by kinetic or enzyme studies.