Previous reports in which
cholesterol homeostasis has been examined in patients with phenotypic
abetalipoproteinemia have shown an increase in whole body
cholesterol synthesis when measured by
sterol balance techniques but normal rates of
cholesterol synthesis when measured by isotopic
cholesterol turnover. Recent studies have indicated that increases in
cholesterol biosynthesis are paralleled by increases in the plasma concentrations of
mevalonic acid and by higher rates of excretion of
mevalonic acid in the urine. In the present report we have measured the 24-h urinary excretion of
mevalonic acid in 7 patients with phenotypic
abetalipoproteinemia and compared this to control subjects. Urinary excretion of
mevalonic acid was significantly higher in the patients with
abetalipoproteinemia (57.2 +/- 10.2 nmol/kg
body weight per day, mean +/- SEM) as compared to control subjects (23.1 +/- 1.5 nmol/kg per day). The magnitude of the increase in urinary
mevalonic acid excretion seen in patients with
abetalipoproteinemia (148%) is greater than the increase in whole body
cholesterol biosynthesis assessed by
sterol balance techniques (57% increase). Our results serve to further validate the usefulness of urinary
mevalonate as an
indicator of relative rates of
cholesterol biosynthesis in humans and suggest that this measurement provides a valuable means to potentially screen for disorders associated with an oversynthesis of
cholesterol.