TURKISH JOURNAL OF PEDIATRICS, vol.44, no.1, pp.49-53, 2002 (Journal Indexed in SCI)
Hyperphenylalaninemia result from a block in the conversion of phenylalanine into tyrosine due to a defect in either the enzyme phenylalanine hydroxylase (98% of subjects) or in the metabolism of the cofactor tetrahydrobiopterin. Phenylalanine hydroxylase deficiency is the most common form of inherited hyperphenylalaninemia disorders, with a prevalence between 1/4,000-1/40,000.