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


Reviewed April 2007

What is the official name of the AHCY gene?

The official name of this gene is “adenosylhomocysteinase.”

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

What is the normal function of the AHCY gene?

The AHCY gene provides instructions for producing the enzyme S-adenosylhomocysteine hydrolase. This enzyme is involved in a multistep process that breaks down the protein building block (amino acid) methionine. Specifically, S-adenosylhomocysteine hydrolase controls the step that converts the compound S-adenosylhomocysteine to the compounds adenosine and homocysteine. This reaction also plays an important role in regulating the addition of methyl groups, consisting of one carbon atom and three hydrogen atoms, to other compounds (methylation). Methylation is important in many cellular processes. These include determining whether the instructions in a particular segment of DNA are carried out, regulating reactions involving proteins and lipids, and controlling the processing of chemicals that relay signals in the nervous system (neurotransmitters).

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

hypermethioninemia - caused by mutations in the AHCY gene

Three mutations in the AHCY gene have been described in people with hypermethioninemia. In a Croatian family, one mutation substitutes the amino acid cysteine for the amino acid tyrosine at protein position 143 (written as Tyr143Cys or Y143C). Another mutation replaces the amino acid tryptophan with a premature stop signal at position 112 (written as Trp112X or W112X), resulting in an enzyme that is abnormally short. A U.S. patient was found to have, in addition to the Y143C mutation, a mutation that substitutes the amino acid valine for the amino acid alanine at position 89 (written as Ala89Val or A89V). These mutations reduce the activity of the S-adenosylhomocysteine hydrolase enzyme, resulting in the signs and symptoms of hypermethioninemia.

Where is the AHCY gene located?

Cytogenetic Location: 20q11.22

Molecular Location on chromosome 20: base pairs 34,234,840 to 34,311,976

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

The AHCY gene is located on the long (q) arm of chromosome 20 at position 11.22.

The AHCY gene is located on the long (q) arm of chromosome 20 at position 11.22.

More precisely, the AHCY gene is located from base pair 34,234,840 to base pair 34,311,976 on chromosome 20.

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

Where can I find additional information about AHCY?

You and your healthcare professional may find the following resources about AHCY 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 AHCY gene or gene products?

  • SAHH

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

What glossary definitions help with understanding AHCY?

alanine ; amino acid ; atom ; compound ; cysteine ; DNA ; enzyme ; gene ; hydrolase ; methionine ; methyl ; methylation ; mutation ; nervous system ; neurotransmitters ; protein ; tryptophan ; tyrosine ; valine

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


  • Barić I, Cuk M, Fumić K, Vugrek O, Allen RH, Glenn B, Maradin M, Pazanin L, Pogribny I, Rados M, Sarnavka V, Schulze A, Stabler S, Wagner C, Zeisel SH, Mudd SH. S-Adenosylhomocysteine hydrolase deficiency: a second patient, the younger brother of the index patient, and outcomes during therapy. J Inherit Metab Dis. 2005;28(6):885-902. (
  • Baric I, Fumic K, Glenn B, Cuk M, Schulze A, Finkelstein JD, James SJ, Mejaski-Bosnjak V, Pazanin L, Pogribny IP, Rados M, Sarnavka V, Scukanec-Spoljar M, Allen RH, Stabler S, Uzelac L, Vugrek O, Wagner C, Zeisel S, Mudd SH. S-adenosylhomocysteine hydrolase deficiency in a human: a genetic disorder of methionine metabolism. Proc Natl Acad Sci U S A. 2004 Mar 23;101(12):4234-9. Epub 2004 Mar 15. (
  • Biochemistry (fifth edition, 2002): Methionine Metabolism (
  • Buist NR, Glenn B, Vugrek O, Wagner C, Stabler S, Allen RH, Pogribny I, Schulze A, Zeisel SH, Barić I, Mudd SH. S-adenosylhomocysteine hydrolase deficiency in a 26-year-old man. J Inherit Metab Dis. 2006 Aug;29(4):538-45. Epub 2006 May 30. (
  • NCBI Gene (
  • Smythies JR, Gottfries CG, Regland B. Disturbances of one-carbon metabolism in neuropsychiatric disorders: a review. Biol Psychiatry. 1997 Jan 15;41(2):230-3. Review. (
  • Turner MA, Yang X, Yin D, Kuczera K, Borchardt RT, Howell PL. Structure and function of S-adenosylhomocysteine hydrolase. Cell Biochem Biophys. 2000;33(2):101-25. Review. (


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: April 2007
Published: February 1, 2016