A newborn baby is well for 3 days, then develops poor feeding and sleepiness that progress to convulsions, coma, and apnea. Hypoglycemia and hyperammonemia are noted on serum chemistry studies. The baby is noted to have urine and perspiration that have a sweetish smell similar to maple syrup. Special metabolic studies demonstrate a deficiency of branched-chain ketoacid decarboxylase. Which of the following amino acids should be avoided in the diet?

A. Histidine
B. Isoleucine
C. Methionine
D. Phenylalanine
E. Tyrosine

B.

The correct answer is B. The disease is maple syrup urine disease, which is also known as branched chain ketoaciduria. This is a rare genetic disease with an incidence of 1 in 200,000 in most of the United States, although a Mennonite community has been found with an incidence of 1 in 1000. The defective enzyme, branched-chain ketoacid dehydrogenase, normally is involved in the catabolism of branched chain amino acids that have been previously transaminated to form their ketoacid derivatives. Leucine, isoleucine, and valine should be eliminated from or minimized in the diet.
Associate abnormal histidine metabolism (choice A) with histidinemia.

Associate abnormal methionine metabolism (choice C) with homocystinuria and cystathioninemia.

Associate abnormal phenylalanine metabolism (choice D) with phenylketonuria.

Associate abnormal tyrosine metabolism (choice E) with tyrosinemia, albinism, and alkaptonuria.