GTP-cyclohydrolase deficiency responsive to sapropterin and 5-HTP supplementation: relief of treatment-refractory depression and suicidal behaviour.

The authors describe a new variant of guanosine triphosphate (GTP)- cyclohydrolase deficiency in a young man with severe and disabling major depressive disorder with multiple near-lethal suicide attempts. His cerebrospinal fluid levels showed that the concentration of tetrahydrobiopterin (BH4), neopterin, 5-hydroxyindoleacetic acid and homovanillic acid were below the reference range, suggesting a defect in the pterin biosynthetic pathway and in synthesis of dopamine and serotonin indicative of GTP-cyclohydrolase deficiency. Patient was started on sapropterin, a BH4 replacement protein, for the defect in the above pathway. In addition, the authors started 5-hydroxytryptophan titrated to 400 mg orally twice daily with concomittant carbidopa 37.5 mg orally four times a day, and he responded with remission of suicidal ideation and significant improvement in depression and function.