ABSTRACT

Short/branched-chain acyl-CoA dehydrogenase (SBCAD) deficiency may be an inborn error of metabolism, which does not manifest clinically unless the patient undergoes some level of metabolic stress. The key to the metabolic abnormality was the excretion of 2-methylbutyrylglycine in the urine and an elevated level of 2-methylbutyrylcarnitine in the blood. SBCAD deficiency is coded for by an autosomal recessive gene on chromosome 10. It was localized to 10q25-q26 by fluorescence in situ hybridization. Defective activity of SBCAD enzyme leads to accumulation of 2-methylbutyryl-CoA and its conjugation products 2-methylbutyrylglycine and 2-methylbutyryl (C5) carnitine. Tandem mass spectrometry has been invaluable for the identification of this disorder of isoleucine metabolism. Patients have been treated with carnitine in doses of 50–100 mg/kg per day and diets restricted in protein or isoleucine, but poor compliance and discontinuation have occurred without obvious clinical consequences.