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http://www.ncbi.nlm.nih.gov/gene?Db=gene&Cmd=ShowDetailView&TermToSearch=3034

Histidinemia, also referred to as histidinuria, is a rare autosomal recessive metabolic disorder caused by a deficiency of the enzyme histidase. Histidase is needed for the metabolism of the amino acid histidine.

Diagnosis and symptoms
Histidenemia is characterized by increased levels of histidine, histamine and imidazole in blood, urine and cerebrospinal fluid. This also results in decreased levels of the metabolite urocanic acid in blood, urine, and skin cells.

Though it may remain asymptomatic for a few years, symptoms will usually present by early childhood. Common symptoms include hyperactivity, speech impediment, developmental delay, learning difficulties, and sometimes mental retardation.

Prevalence


Histidinemia is a somewhat rare disorder. However, in Japan, it is the single most prevalent inborn error of metabolism.