Abstract This study reports a boy with psychomotor retardation and epilepsy due to maternal phenylketonuria (PKU). The boy was admitted at the age of 20 months because of psychomotor retardation and epilepsy. He had seizures from the age of 1 year. His development quotient was 43. He presented with microcephaly, normal skin and hair color. Brain MRI scan showed mild cerebral white matter demyelination, broadening bilateral lateral ventricle and foramen magnum stricture. Chromosome karyotype, urine organic acids, blood amino acids and acylcarnitines were normal. His mother had mental retardation from her childhood. She presented with learning difficulties and yellow hair. Her premarriage health examinations were normal. She married a healthy man at age of 26 years. When she visited us at 28 years old, PKU was found by markedly elevated blood phenylalanine (916.54 μmol/L vs normal range 20-120 μmol/L). On her phenylalanine hydroxylase (PAH) gene, a homozygous mutations c.611A>G (p.Y204C) was identified, which confirmed the diagnosis of PAH-deficient PKU. Her child carries a heterozygous mutation c.611A>G with normal blood phenylalanine. Her husband had no any mutation on PAH. It is concluded that family investigation is very important for the etiological diagnosis of the children with mental retardation and epilepsy. Carefully clinical and metabolic survey should be performed for the parents with mental problems to identify parental diseases-associated child brain damage, such as maternal PKU.
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