The concept that an absence of
apoprotein B in plasma may result in increased
cholesterol biosynthesis was investigated by
sterol balance techniques in 2 male patients with
abetalipoproteinemia, one an adult, the other a child. Total body synthesis of
cholesterol in both the adult patient (19.3 +/- 3.8 mg/kg/day vs. 10.8 +/- 0.9 mg/kg/day in controls) and the child with
abetalipoproteinemia (34.9 mg/kg/day vs. 14.5 +/- 3.8 mg/kg/day in control children) was significantly higher than in controls whereas
bile acid synthesis was similar in both groups. Absorption of orally administered [1,2-3H]
cholesterol was lower in the abetalipoproteinemic subjects than the controls and subsequent labeling of plasma
cholesterol in the former patients was minimal (less than 3% of controls). The mechanisms for the increased
sterol synthesis in
abetalipoproteinemia may relate to the absence of
chylomicrons and
low density lipoproteins in plasma, but the magnitude of the increase can be largely explained on the basis of enhanced
sterol losses that occur secondary to malabsorption of biliary
cholesterol.