AMN

Amn, in a biomedical context, most commonly refers to the AMN gene, which encodes the amnionless protein. Amnionless is a transmembrane component of a receptor complex that includes cubilin (CUBN) and is expressed on the apical surfaces of intestinal enterocytes and renal proximal tubular cells. The AMN–CUBN receptor mediates endocytosis of several ligands, most notably the intrinsic factor–vitamin B12 complex, enabling intestinal absorption and renal reabsorption of cobalamin and related proteins.

Mutations in AMN disrupt this receptor function, causing impaired intestinal absorption of vitamin B12 and, in many cases, renal proteinuria. This combination is characteristic of Imerslund-Gräsbeck syndrome (IGS), a rare inherited disorder. Patients typically present with vitamin B12 deficiency that can lead to anemia and, in some cases, neurological symptoms, along with varying degrees of proteinuria. Biochemical testing shows low serum cobalamin with elevated methylmalonic acid and homocysteine. Diagnosis is confirmed by genetic testing identifying pathogenic variants in AMN or, less commonly, in CUBN.

Treatment focuses on correcting B12 deficiency, usually with regular parenteral or high-dose oral vitamin B12; this can resolve anemia and prevent progression of symptoms. The prognosis depends on timely diagnosis and management. Beyond human health, AMN is primarily used as a gene symbol in genetics and protein biochemistry; other uses of the acronym are context-dependent.