Urocanic aciduria

Urocanic aciduria (also known as urocanase deficiency or urocanic acid storage disease) is an extremely rare inborn error of histidine metabolism caused by a deficiency of the enzyme urocanase (also called urocanic acid hydratase), which catalyzes the second step in the degradation pathway of histidine. This enzyme deficiency leads to the accumulation of urocanic acid in the urine and blood. The condition is classified under disorders of histidine metabolism (ICD-10: E70.8). The clinical significance of urocanic aciduria remains uncertain, as only a very small number of cases have been reported in the medical literature. Some affected individuals have presented with intellectual disability and developmental delay, while others identified through biochemical screening have been clinically asymptomatic. Additional features reported in some cases include short stature and behavioral difficulties, though it is unclear whether these findings are causally related to the metabolic defect or represent coincidental associations. The nervous system appears to be the primary system of concern when clinical manifestations are present. There is currently no specific treatment for urocanic aciduria. Management, when deemed necessary, is supportive and symptom-based. A low-histidine diet has been attempted in some cases, but its clinical efficacy has not been established. Given the very limited number of reported patients and the variable clinical presentation, the natural history and long-term prognosis of this condition remain poorly defined. Genetic counseling is recommended for affected families.

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