<prompt> Deficiency of enzyme a-keto acid decarboxylase leading to a block in the metabolism of branch chain amino acids is observed inMaple syrup urine diseaseHanups diseaseAlkaptonuriaPhenylketonuria  <response>: Maple syrup urine diseaseMSUD is due to increased activity of branched chain alpha ketoacid dehydrogenaseBCKAD complex,a mitochondrial enzyme involved in degradation of branched chain amino acidsleucine,isoleucine, and valine.This enzyme has 4 subunits:E1alpha,E1beta,E2 and E3. Reference:Essential pediatrics-Ghai,8th edition,page no:652 