Abetalipoproteinemia

Abstract

In this volume on low density lipoproteins (LDL), the inclusion of a chapter concerned with the most severe aberration of this lipoprotein species, namely its absence, may require some justification. Perhaps the most satisfactory explanation is to call attention to the overlapping heterogeneity of the lipoprotein classes and to emphasize the interdependence of all the human lipoproteins. The intensive study of patients with abetalipoproteinemia (ABL) has provided a wealth of information for investigators interested in lipid metabolism, lipoprotein structure and function, as well as for hematologists, neurologists, gastroenterologists, and ophthalmologists. I do not intend to cover most of the areas just mentioned, since recent reviews provide adequate reference material.^1,2 Abnormalities in the composition of the high density lipoproteins (HDL), in particular of the A apoproteins, and of the C apoproteins will be reviewed. There have been several studies of the activity of lecithin: cholesterol acyltransferase (LCAT) in patients with abetalipoproteinemia; although there are important differences in the assay systems used by the different groups, there is consensus that the enzyme activity is reduced in patients with ABL. These studies and the consequences of decreased LCAT activity will also be reviewed. It also seems appropriate in this chapter to comment upon certain genetic relationships that have been reported between hypobetalipoproteinemia and abetalipoproteinemia.