Propionyl-CoA carboxylase deficiency in a patient with biotin-responsive 3-methylcrotonylglycinuria.

Summary: The abnormal metabolites 3-hydroxypropionic acid (1.6–4.0 mg/day) and methylcitric acid (3.7–5.8 mg/day) were identified and quantitated in the urine of a patient in whom biotin-responsive 3-methylcrotonylglycinuria and deficiency of 3-methylcrotonyl-CoA carboxylase had previously been documented. The level of excretion of these metabolites was in the lower range of those found in patients with propionic acidemia in whom there is a deficiency of propionyl-CoA carboxylase. The activity of this enzyme in fibroblasts derived from the patient and grown in media low in biotin was 4% of normal. This is in the range of patients with propionyl-CoA carboxylase deficiency. Documented deficiency in this patient of two carboxylases, both of which contain biotin, suggests that the primary defect is in the metabolism of biotin. Speculation: The deficiency of two mitochondrial carboxylases in a patient suggests the presence of a fundamental defect in either the transport of biotin or in the holocarboxylase synthetase that attaches biotin covalently to both carboxylases.