Hypertryptophanemia

Hypertryptophanemia (also known as familial hypertryptophanemia or tryptophanemia) is an extremely rare inborn error of amino acid metabolism characterized by elevated levels of tryptophan in the blood and urine. The condition is thought to result from a defect in the enzyme tryptophan 2,3-dioxygenase (TDO2), which catalyzes the first and rate-limiting step in the kynurenine pathway of tryptophan degradation. This enzymatic deficiency leads to accumulation of tryptophan and its metabolites, including indolic compounds, in body fluids. The condition primarily affects the nervous system. Clinical features reported in the very small number of documented cases include intellectual disability (cognitive impairment), behavioral abnormalities, mood disturbances, and exaggerated affective responses. Some patients have also been described with skin photosensitivity and ocular abnormalities. However, the clinical significance of hypertryptophanemia remains debated, as some individuals with elevated tryptophan levels have been reported to be clinically asymptomatic, raising the question of whether the biochemical finding is always pathogenic or may represent a benign metabolic variant in some cases. There is no specific curative treatment for hypertryptophanemia. Management is primarily supportive and may include dietary modification to restrict tryptophan intake, along with developmental and behavioral interventions as needed. Given the extreme rarity of this condition, with only a handful of families reported in the medical literature, evidence-based treatment guidelines are not established. Genetic counseling is recommended for affected families.

Common questions about Hypertryptophanemia