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Hyperphenylalaninemia (HPA) may rarely be caused by defects in the synthesis or recycling of tetrahydrobiopterin (BH4), an essential co-factor in the phenylalanine hydroxylase activity (PAH) reaction. Approximately 2% of pacients with HPA have a defect in one of the four enzymes responsible for maintaining BH4 levels. Guanosine triphosphate cyclohydrolase (GTPCH) and pyruvoyltetrahydrobiopterin synthase (PTPS) are essential enzymes for biosynthesis, whereas pterin-4α-carbinolamine dehydratase (PCD) and dihydropteridine reductase (DHPR) are responsible for recycling. The case report is about two different children with two years old, one of them with defect in GTPCH and other in DHPR. P.S.F. presented hypotonia with 3 months and constated a delayed neuropsicomotor developmental (DNMD) in the first year of life. Neurologic exam certified pyramidal signs and trunk hypotonia. During the diagnostic investigation, was observed HPA with seric anormal values, but no high, which seems not compatible with phenilketonuria (PKU) diagnostic. The possibility was a secondary HPA, with a different enzyme defect. Complementary exam estabilished very low levels of neopterin and biopterin that indicates GTPCH defect. Other child, J.P.F.S., began clinical manifestations with epilepsy around 2 months and DNMD. The parents are consanguines. Neurologic exam demonstrated irritability and hypotonia. The inborn metabolism errors screen showed elevated seric phenylalanine and normal tyrosine. Adicional laboratory investigation confirmed DHPR absent activity. Biopterin disorders result in deficiencies of the neurotransmitters L-dopa and 5-hydroxytryptophan. Should be highlighted the early treatment could be modify the prognostic and register a rare cases of HPA without PKU.

Hyperphenylalaninemia; Biopterin Disorder; hypotonia; delayed neuropsicomotor developmental