Successful long term therapy of biopterin deficiency.

A hyperphenylalaninaemic infant, started on dietary therapy at 14 days of age, had severe developmental retardation and neurological abnormalities despite excellent biochemical control. A diagnosis of a deficit in biopterin synthesis was made at five months of age as a result of the following: high neopterin and low biopterin levels in both blood and urine, normal dihydropteridine reductase in the liver and a sharp drop in the plasma phenylalanine level 4 h after the administration of a test dose of tetrahydrobiopterin. Treatment with levodopa, carbidopa and 5-hydroxytryptophan resulted in prompt neurological improvement.