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AHCY gene


Normal Function

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).

Health Conditions Related to Genetic Changes


More than 10 variants (also known as mutations) in the AHCY gene have been described in people with hypermethioninemia. Most of these variants substitute one amino acid for another amino acid in the S-adenosylhomocysteine hydrolase enzyme, causing it to process methionine less efficiently. Other variants introduce a premature stop signal in the instructions for making the S-adenosylhomocysteine hydrolase enzyme. As a result, a shortened, nonfunctional enzyme is produced. These changes reduce the activity of the S-adenosylhomocysteine hydrolase enzyme, impairing the breakdown of methionine. As a result, methionine builds up in the body, which is known as hypermethioninemia. In some cases, excess methionine can cause intellectual disability or other neurological problems in affected individuals.

More About This Health Condition

Other Names for This Gene

  • SAHH

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • Baric I, Cuk M, Fumic 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. doi: 10.1007/s10545-005-0192-9. Citation on PubMed or Free article on PubMed Central
  • 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. doi: 10.1073/pnas.0400658101. Epub 2004 Mar 15. Citation on PubMed or Free article on PubMed Central
  • Biochemistry (fifth edition, 2002): Methionine Metabolism
  • Buist NR, Glenn B, Vugrek O, Wagner C, Stabler S, Allen RH, Pogribny I, Schulze A, Zeisel SH, Baric I, Mudd SH. S-adenosylhomocysteine hydrolase deficiency in a 26-year-old man. J Inherit Metab Dis. 2006 Aug;29(4):538-45. doi: 10.1007/s10545-006-0240-0. Epub 2006 May 30. Citation on PubMed or Free article on PubMed Central
  • 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. doi: 10.1016/S0006-3223(96)00068-6. No abstract available. Citation on PubMed
  • 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. doi: 10.1385/CBB:33:2:101. Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.