Increased urinary mevalonic acid excretion in patients with abetalipoproteinemia and homozygous hypobetalipoproteinemia

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.