Urocanase deficiency

Urocanase deficiency is a very rare autosomal recessive disorder that may be benign in most affected individuals. The reported cases with the disorder are less than ten. The enzyme defect is urocanase, an enzyme normally expressed in liver. The block in conversion of urocanic acid to imida-... 

Two patients identified by routine newborn urine screening have maintained normal development without dietary or other therapy. Dietary treatment is not indicated for this disorder although the treatment might be considered in the patients with urocanase deficiency who have clinical abnormalities. 

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The responses of histidine and its metabolites in blood and urine to histidine and urocanic acid loads in patients with histidinemia, urocanase deficiency and formiminotransferase deficiency. 

The histidinemic urine is sometimes only weakly positive or negative on ferric chloride testing, which reflects either the instability of imidazole-pyruvic acid, the relation of its excretion to protein intake, immaturity of histidine transaminase, or a combination of these factors. Even after histidine loading, histidinemic neonates excrete much smaller quantities of imi-dazolepyruvic acid than do older children. In patients with urocanase deficiency, the levels of blood histidine and urine imidazolepyruvic acid are normal or slightly elevated. Therefore, it is necessary to do a quantitative analysis of blood histidine and urine ferric chloride test in order to overlook the patients with this condition. 

Prenatal diagnosis is not indicated for histidinemia and urocanase deficiency because these disorders are probably harmless. 

Restricting dietary histidine will bring the blood histidine level back to normal and eliminates the urinary imidazole metabolites in patients with histidinemia and urocanase deficiency. However, no urgent treatment is required because of the benign nature of this condition. 

Although cDNAs encoding human histidase and formiminotransferase have already been cloned, mutation analysis is not performed in patients with histidinemia and formiminotransferase deficiency. cDNA for human urocanase is not cloned. 

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