Deficiency of enzyme a-keto acid decarboxylase leading to a block in the metabolism of branch chain amino acids is observed in -

Ans. is 'a' i.e., Maple Syrup urine diseaseMAPLE SYRUP URINE DISEASE In this disorder, the branched-chain keto acids derived from isoleucine, leucine, and valine appear in the urine, giving it a maple syrup-like odor.This condition results from a deficiency in the branched-chain -keto acid dehydrogenase.It is a mitochondrial, enzyme complex consisting of a-ketoacid decarboxylase , Dihydrolipoyl dehydrogenase and Transacylase The early steps in the metabolism of these three amino-acids are similar. One of the steps - decarboxylation is accomplished by a complex enzyme system i.e. branched chain oc-keto acid dehydrogenase using thiamine pyrophosphate (vitamin B1) as a coenzyme.The elevated keto acids cause severe brain damage, with death in the first year of life.The disease is characterized by feeding problems,vomiting, dehydration, severe metabolic acidosis, and a characteristic maple syrup odor to the urine. If untreated, the disease leads to mental retardation, physical disabilities, and even death.Treatment. A few cases respond to megadoses of thiamine (vitamin B1). Otherwise, synthetic diets low in branched-chain amino acids are given.