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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed August 2009

What is the official name of the HAL gene?

The official name of this gene is “histidine ammonia-lyase.”

HAL is the gene's official symbol. The HAL gene is also known by other names, listed below.

What is the normal function of the HAL gene?

The HAL gene provides instructions for making an enzyme called histidase. Histidase breaks down the amino acid histidine, a building block of most proteins. Histidase is active (expressed) primarily in the liver and the skin. This enzyme breaks down histidine to a molecule called urocanic acid. In the liver, urocanic acid is broken down to form another amino acid called glutamic acid. In the skin, urocanic acid is involved in the response to ultraviolet (UV) light.

How are changes in the HAL gene related to health conditions?

histidinemia - caused by mutations in the HAL gene

At least four mutations in the HAL gene have been found to cause histidinemia. All of these mutations change single amino acids in the histidase enzyme. These mutations are thought to decrease or eliminate enzyme activity, resulting in an inability to break down histidine. Histidine that is not broken down accumulates in the blood, but it typically causes no health problems.

Where is the HAL gene located?

Cytogenetic Location: 12q23.1

Molecular Location on chromosome 12: base pairs 95,972,662 to 95,996,365

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The HAL gene is located on the long (q) arm of chromosome 12 at position 23.1.

The HAL gene is located on the long (q) arm of chromosome 12 at position 23.1.

More precisely, the HAL gene is located from base pair 95,972,662 to base pair 95,996,365 on chromosome 12.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about HAL?

You and your healthcare professional may find the following resources about HAL helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the HAL gene or gene products?

  • HIS
  • histidase
  • HSTD

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding HAL?

acids ; amino acid ; ammonia ; enzyme ; expressed ; gene ; glutamic acid ; His ; histidine ; molecule

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Eckhart L, Schmidt M, Mildner M, Mlitz V, Abtin A, Ballaun C, Fischer H, Mrass P, Tschachler E. Histidase expression in human epidermal keratinocytes: regulation by differentiation status and all-trans retinoic acid. J Dermatol Sci. 2008 Jun;50(3):209-15. doi: 10.1016/j.jdermsci.2007.12.009. Epub 2008 Feb 15. (
  • Kawai Y, Moriyama A, Asai K, Coleman-Campbell CM, Sumi S, Morishita H, Suchi M. Molecular characterization of histidinemia: identification of four missense mutations in the histidase gene. Hum Genet. 2005 Apr;116(5):340-6. Epub 2005 Jan 27. Erratum in: Hum Genet. 2005 Dec;118(3-4):531-2. (
  • NCBI Gene (
  • Suchi M, Sano H, Mizuno H, Wada Y. Molecular cloning and structural characterization of the human histidase gene (HAL). Genomics. 1995 Sep 1;29(1):98-104. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: August 2009
Published: February 8, 2016