Beta-methylcrotonic aciduria associated with lactic acidosis.

A patient is described in whom lactic acidosis of very severe degree was found to coincide with the presence of beta-methylcrotonic acid and rho-hydroxyphenyllactic acid in urine in large amounts, while beta-hydroxyisovaleric acid was found to be a relatively minor excretion product. Beta-methylcrotonic acid is demonstrated, for the first time, to be present in blood and CSF. These findings are discussed in relation to the patients previously reported to have beta-methylcrotonylglycinuria and raise the possibility that our patient's organic aciduria may be secondary to acquired disease rather than to an inborn error of metabolism.