A normal born child presents with mental retardation, blond hair and convulsions at 1 year of age. Most probable diagnosis is?

Ans. (b) PhenylketonuriaRef Nelson 18th ed chapter 85.1, Harrison's 17th Ed Ch 358Classic Phenylketonuria Clinical Manifestations* The affected infant is normal at birth.* Mental retardation may develop gradually and may not be evident for the 1st few months.* Vomiting, sometimes severe enough to be misdiagnosed as pyloric stenosis, may be an early symptom.* Older untreated children become hyperactive, with purposeless movements, rhythmic rocking, and Athetosis.* Infants are lighter in their complexion than unaffected siblings with blonde hair.* These children have an unpleasant odor of Phenyl-acetic acid, which has been described as musty or mousey.* Most infants are hypertonic with hyperactive deep tendon reflexes.* About 25% of children have seizures, and more than 50% have electroencephalographic abnormalities.* Microcephaly, prominent maxilla with widely spaced teeth, enamel hypoplasia, and growth retardation are other common findings in untreated children.