Phenylketonuria (PKU). Biopterin dependent PKU. 6PTS (6-pyruvoyltetrahydropterin) deficiency
Incidence
Approx. 70 cases known. It is a disorder of BH4 synthesis.
Clinical Characteristics
Can be mild to severe, or start with early onset encephalopathy, with seizures, myoclonus, respiratory & cardiac difficulties, with extrapyramidal Sx, such as cogwheel rigidity, bradykinesia (infantil Parkinsonism). Hyperphenylalaninemia is mild, and the excreted related organic acids are lower than classical PKU.
Precipitants
no
Provocation Tests
BH4 5-20 mg/kg/day administration will decrease blood phenylalanine to normal limits, urine biopterin increase to normal limits and biopterin will appear in urine.
Diagnostic Procedures
Ferric chloride gives emerald green transient color. Urine pterins determination. Patients have a greatly increased neopterin/biopterin ratio. EB-RBC