Phenylalanine hydroxylase deficiency: intelligence of patients after early dietary treatment

Neonatal screening for hyperphenylalaninemia (HPA) has been performed in Taiwan for more than 20 years. In this paper, we studied 21 cases of HPA caused by phenylalanine hydroxylase (PAH) deficiency. These patients were detected by a single newborn screening center over ten-years, and the incidence was one in 63,690. According to the initial plasma phenylalanine levels, four of the 21 patients belonged to classical phenylketonuria (PKU), seven were mild PKU, and ten were mild HPA. They commenced diet control at the age of 47 +/- 22 (17-106) days. Fourteen patients completed IQ tests, three of the 14 patients having classical PKU, five having mild PKU, and six having mild HPA. Their average IQ scores were within normal ranges (full-scale IQ 98 +/- 14, verbal IQ 92 +/- 8, and performance IQ 104 +/- 19), but patients with classical PKU tended to have lower IQ scores than other patients. Since classical PKU is rare in Taiwan, further studies including detailed neuropsychological tests will be required to evaluate the effect of treatment in this group of patients.