Cholesterol balance studies were carried out twice in a young male patient with homozygous familial hypercholesterolemia. At 13 mo, cholesterol balance in this patient averaged 31.3 mg/kg per d, and bile acid excretion was 12.0 mg/kg per d; at 3 yr, results were similar, 27.3 and 15.5 mg/kg per d for cholesterol balance and bile acids, respectively. A normal boy of 3 yr was also studied for comparison with the second study in the authors' patient. Cholesterol balance and bile acid outputs in the normal child were 11.5 and 3.3 mg/kg per d, respectively. Thus, in comparison with the normal child, the patient with homozygous familial hypercholesterolemia had a marked increase in synthesis of cholesterol and bile acids. Although synthesis of bile acids was high in this patient, the fraction of newly synthesized cholesterol converted into bile acids (40-56%) was in the normal range; this suggests that the enhanced output of bile acids was secondary to an increased synthesis of cholesterol and not to malabsorption of bile acids, which likely would have produced a higher fractional conversion. Although the patient has been studied at a younger age than any reported in the literature, two similar children 5 and 6 yr of age were also observed to have elevated cholesterol synthesis.
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