Question

A 1-year-old girl is brought to her pediatrician’s office with concerns about her development. She had an uncomplicated birth outside the United States at term. The mother reports that the baby is not achieving the normal milestones for a baby of her age. She also reports an unusual odor to her urine and some areas of hypopigmentation on her skin and hair. On exam, the girl is noted to have some muscle hypotonia and microcephaly. The urine collected is found to have a “mousy” odor.

the likely Diagnosis is Phenylketonuria (PKU)

*** Why are the CNS effects now rarely seen??

Answer 1

Phenylketonuria (PKU) is a condition that results from the presence of excess Phenylalanine, an Amino acid in the bloodstream. This is because of a deficiency of an enzyme called Phenylalanine Hydroxylase (PAH) which is required for Phenylalanine metabolism. In the absence of PAH, Phenylpyruvate, an intermediate accumulates and the body is unable to synthesize Tyrosine, the deficiency of which leads to neurological defects.

These days, PKU does not lead to Neurological defects as PKU can be managed by adhering to a specialized diet low in Phenylalanine, with some supplemental Tyrosine. By managing diet since birth Neurological defects are avoided.