Autosomal recessive GTP cyclohydrolase I deficiency

Lore & Background

Patients with autosomal recessive GTP cyclohydrolase I deficiency may present with developmental delay, axial hypotonia, delayed speech development, or dysarthria. Motor disturbances include dystonia, oculogyric crises, and parkinsonism/hypokinesia, and psychiatric symptoms are possible. Biochemically, patients show hyperphenylalaninemia and usually have decreased levels of biopterin and neopterin in urine and dry blood spots.

Reader's Guide

Autosomal recessive GTP cyclohydrolase I deficiency is significant as a rare inborn error of metabolism affecting both neurotransmitter synthesis and phenylalanine homeostasis. Its recognition as one of six known causes of tetrahydrobiopterin deficiency and as part of the dopa-responsive dystonia spectrum has guided diagnostic and therapeutic approaches. Treatment, per a 2020 consensus guideline, may include a phenylalanine-restricted diet, sapropterin (an artificial tetrahydrobiopterin analogue), L-DOPA, and 5-hydroxytryptophan. Prolonged high-dose L-DOPA therapy can lead to cerebral folate deficiency, necessitating folinic acid supplementation to restore folate status. The condition highlights the interplay between cofactor deficiencies and neurotransmitter disorders, and its management requires careful monitoring of both metabolic and neurological parameters.

Did You Know?

• Patients may present with oculogyric crises and parkinsonism/hypokinesia.
• Prolonged therapy with large doses of L-DOPA may lead to cerebral folate deficiency.