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At a glance

Histidinemia is a rare hereditary metabolic disorder characterized by a deficiency of the enzyme histidase, which is necessary for the metabolism of the amino acid histidine. The majority of individuals are asymptomatic.


Histiduria; Histidase Deficiency Syndrome; Histidine Ammonia-Lyase Deficiency; HAL Deficiency; HIS Deficiency; Hyperhistidinemia.


In a study of more than 20 million newborns, the incidence of this disease was estimated to be 1:11,500 births. This medical condition seems to be most prevalent among people of French Canadian or Japanese descent. In Japan, the incidence is reported to be 1:9,500 infants. In the Province of Quebec, Canada, the incidence is estimated approximately 1:8,600 infants.

Genetic inheritance

Histidinemia is inherited as an autosomal recessive trait and is considered one of the most common inborn errors of metabolism. It is present at birth and affects males and females in equal numbers. It is now thought to be a primarily benign disorder.


Histidinemia 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. A typical characteristic of histidinemia is an increase in the blood histidine levels from normal levels (70-120 µM) to an elevated level (290-1420 µM).

Clinical aspects

Histidinemia is considered a benign condition. For years, it was believed that mental retardation and speech defects were associated with histidinemia; however, it has now been established that these findings are coincidental. Infants with histidinemia are asymptomatic. Individuals with histidinemia have elevated levels of the amino acid histidine in the blood and excessive amounts of histidine, imidazole pyruvic acid, and other imidazole metabolism products in the urine.

Anesthetic considerations

No specific anesthetic considerations with this medical condition.

Other condition to be considered

  • Histidinuria due to Renal Tubular Defect: Disorder characterized by mild mental retardation and histidinuria despite normal blood levels. Histidine loading showed impaired intestinal absorption. Clinical findings include myoclonic seizures, sensorineural deafness, thin upper lips and long shallow philtrum, and short thick fingers and toes. Radiologically, the middle phalanges are short, rounded, and abnormally shaped. The inheritance is presumably autosomal recessive transmission.


Lam  WK, Cleary  MA, Wraith  JE,  et al: Histidinemia: A benign metabolic disorder. Arch Dis Child 74:343–346, 1996.  [PubMed: 8669938]
Lemieux  B: Newborn urine screening experience with over one million infants in the Quebec network of genetic medicine. J Inherit Metab Dis 11:45, 1988.  [PubMed: 3128688]

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