High density lipoprotein metabolism in a patient with abetalipoproteninemia

The concentration of individual plasma apoproteins together with the in vivo metabolism of 125I-labelled high density lipoprotein was studied in an adult male patient with abetalipoproteinemia. Plasma concentrations of cholesterol (26 mg/dl) and triglyceride (5 mg/dl) were markedly reduced and apoprotein B was absent. The concentrations of apo AI, apo AII, CI, CII, CIII and E were also lower than in normal subjects. To further evaluate these changes we studied the in vivo metabolism of autologous 125I-labelled HDL over a period of 13 days. The plasma half-life (4.1 days) and fractional catabolic rate (0.23) were similar to previously reported values for the normal subjects, but overall synthesis of apoproteins AI (5.7 mg/kg/day) and AII (3.6 mg/kg/day) were significantly reduced. After separation of delipidated HDL apoproteins by polyacrylamide-gel electrophoresis we were unable to demonstrate any difference in the half-life or fractional catabolic rates of apoproteins AI and AII and CII pulu CIII. We conclude that the low concentrations of apoproteins AI and AII in the plasma of our patient with abetalipoproteinemia are a consequence of reduced synthesis and do not reflect enhanced catabolism