Central Tegmental Tract Involvement in an Infant with 6-Pyruvoyltetrahydropterin Synthetase Deficiency

SUMMARY: We report the case of an asymptomatic 2-month-old infant with 6-pyruvoyltetrahydrop-terin synthetase deficiency detected through a neonatal phenylketonuria screening program. MR imaging revealed symmetrical lesions in the central tegmental tract with reduced diffusion, which resolved after treatment. A possible explanation for these lesions is intramyelinic edema resulting from brain insults in utero. Tetrahydrobiopterin (BH4) deficiency comprises a heterog-enous group of disorders caused bymutations of one of the genes encoding enzymes involved in the synthesis or regener-ation of BH4. 1 It presents mostly with hyperphenylalaninemia (HPA) and a deficiency of neurotransmitter precursors L-dopa and 5-hydroxytryptophan and may be detected through neonatal phenylketonuria (PKU) screening pro-grams. BH4 deficiency (1/1,000,000) is much rarer than PKU (1/10,000). 6-Pyruvoyltetrahydropterin synthetase (PTPS) deficiency is the most common enzyme defect of BH4 defi