Background
Histidine ammonia-lyase is a cytosolic enzyme catalyzing the first reaction in histidine catabolism, the nonoxidative;deamination of L-histidine to trans-urocanic acid. Histidine ammonia-lyase defects cause histidinemia which is;characterized by increased histidine and histamine and decreased urocanic acid in body fluids. Several transcript;variants encoding different isoforms have been found for this gene.