182)Answer

D. Phenylketonuria

Rationale

•In untreated children with phenylketonuria (PKU), the hallmark of the disease is mental retardation. Other characteristics include fair skin, abnormal gait and posture, stunted growth, and urine with a musty odor.

•PKU is an autosomal recessive metabolic disorder. Absence of the liver enzyme phenylalanine hydroxylase prevents conversion of phenylalanine, an essential amino acid, into tyrosine. As a result, excessive phenylalanine builds up in the blood stream and tissues causing permanent damage to brain tissue.

•Branched-chain ketoaciduria, or maple syrup urine disease, causes an inability to break down branched-chain amino acids, leading to a buildup of waste products.

•Celiac disease is an autoimmune disorder in which gluten triggers an inflammatory response in the digestive tract.

•Tay-Sach’s disease causes an inability to break down phospholipids, causing lipid accumulation in the brain and a rapid deterioration of mental and physicial abilities.