A 6-day-old newborn, who is being breast-fed, is brought to the ER because he is unresponsive. He has been vomiting and is lethargic for the past 2 days. Examination shows an obtunded infant with hypertonia and muscle rigidity. A peculiar odor of burnt sugar is noted in his diaper. The plasma concentration of which of the following amino acids is most likely to be increased in this patient?

Question

Quizplus · Accepted Answer

The symptoms and the burnt sugar odor suggest Maple Syrup Urine Disease, which is caused by a defect in the breakdown of branched-chain amino acids, leading to increased levels of leucine, isoleucine, and valine.  Maple syrup urine disease (MSUD), also called branched-chain aminoaciduria, is so called because the urine of affected individuals smells like maple syrup or burnt sugar. MSUD results from a deficiency in an enzyme, branched-chain a-keto acid dehydrogenase (BCKD), that is involved in the catabolism of the branched-chain amino acids (BCAAs), leucine, isoleucine, and valine.

A 6-Day-Old Newborn, Who Is Being Breast-Fed, Is Brought to the ER