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AMN gene
URL of this page: https://medlineplus.gov/genetics/gene/amn/

AMN gene

amnion associated transmembrane protein

Normal Function

The AMN gene provides instructions for making a protein called amnionless that spans the membranes of cells in the intestines and the kidneys. Amnionless helps the body absorb vitamin B12 (also called cobalamin) from food, which is important because the body cannot make this vitamin. Vitamin B12 is essential for the formation of DNA and for the chemical reactions that convert food into energy (energy metabolism). Vitamin B12 also plays a key role in making red blood cells and maintaining the nerve cells in the brain and spinal cord (central nervous system).

Amnionless binds to another protein called cubilin to form a complex called the cubam receptor. In the small intestine, cubilin can interact with vitamin B12 while it is anchored to the cell membrane by amnionless.

During digestion, vitamin B12 binds to intrinsic factor, which helps the intestines absorb vitamin B12. Vitamin B12 and intrinsic factor then bind to cubilin as they pass through the small intestine. Amnionless helps transfer this whole complex into the intestinal cells. Vitamin B12 is then released into the blood and travels throughout the body. In the kidneys, amnionless and cubilin help return proteins to the bloodstream (reabsorption) that would otherwise be released in the urine.

Health Conditions Related to Genetic Changes

Imerslund-Gräsbeck syndrome

Changes in the AMN gene cause Imerslund-Gräsbeck syndrome. Genetic changes that cause disease are called pathogenic variants. Imerslund-Gräsbeck syndrome is characterized by problems with the body's ability to absorb vitamin B12, which can lead to a blood disorder called megaloblastic anemia. Megaloblastic anemia occurs when a person has a low number of red blood cells (anemia) and the remaining red blood cells are larger than normal (megaloblastic). Affected individuals frequently have excess protein in their urine (proteinuria).

Some of the pathogenic variants that are associated with Imerslund-Gräsbeck syndrome cause cells to produce a version of amnionless that cannot bind to cubilin, while others prevent amnionless from reaching the cell membrane. These changes impair the intestinal absorption of vitamin B12 and reduce the amount of vitamin B12 that is available for the body to use. This affects the development of red blood cells, leading to megaloblastic anemia. When there is not enough amnionless in the membranes of kidney cells, proteins are released in the urine instead of being reabsorbed into the body.

More About This Health Condition

Other Names for This Gene

  • amnionless

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

References

  • Beech CM, Liyanarachchi S, Shah NP, Sturm AC, Sadiq MF, de la Chapelle A, Tanner SM. Ancient founder mutation is responsible for Imerslund-Grasbeck Syndrome among diverse ethnicities. Orphanet J Rare Dis. 2011 Nov 13;6:74. doi: 10.1186/1750-1172-6-74. Citation on PubMed or Free article on PubMed Central
  • Fyfe JC, Madsen M, Hojrup P, Christensen EI, Tanner SM, de la Chapelle A, He Q, Moestrup SK. The functional cobalamin (vitamin B12)-intrinsic factor receptor is a novel complex of cubilin and amnionless. Blood. 2004 Mar 1;103(5):1573-9. doi: 10.1182/blood-2003-08-2852. Epub 2003 Oct 23. Citation on PubMed
  • Kingma SDK, Neven J, Bael A, Meuwissen MEC, van den Akker M. Imerslund-Grasbeck syndrome: a comprehensive review of reported cases. Orphanet J Rare Dis. 2023 Sep 14;18(1):291. doi: 10.1186/s13023-023-02889-x. Citation on PubMed
  • Kozyraki R, Cases O. Vitamin B12 absorption: mammalian physiology and acquired and inherited disorders. Biochimie. 2013 May;95(5):1002-7. doi: 10.1016/j.biochi.2012.11.004. Epub 2012 Nov 20. Citation on PubMed
  • Namour F, Dobrovoljski G, Chery C, Audonnet S, Feillet F, Sperl W, Gueant JL. Luminal expression of cubilin is impaired in Imerslund-Grasbeck syndrome with compound AMN mutations in intron 3 and exon 7. Haematologica. 2011 Nov;96(11):1715-9. doi: 10.3324/haematol.2011.043984. Epub 2011 Jul 12. Citation on PubMed or Free article on PubMed Central
  • Udagawa T, Harita Y, Miura K, Mitsui J, Ode KL, Morishita S, Urae S, Kanda S, Kajiho Y, Tsurumi H, Ueda HR, Tsuji S, Saito A, Oka A. Amnionless-mediated glycosylation is crucial for cell surface targeting of cubilin in renal and intestinal cells. Sci Rep. 2018 Feb 5;8(1):2351. doi: 10.1038/s41598-018-20731-4. Citation on PubMed
  • Watkins D, Rosenblatt DS. Lessons in biology from patients with inborn errors of vitamin B12 metabolism. Biochimie. 2013 May;95(5):1019-22. doi: 10.1016/j.biochi.2013.01.013. Epub 2013 Feb 10. Citation on PubMed

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