B2M Gene

B2M (B2M stands for "beta2-microglobulin") is a protein-coding gene located on chromosome 15q21.1. The B2M gene encodes a serum protein (beta-2-microglobulin) that is found in association with the major histocompatibility complex (MHC) class I heavy chain on the surface of almost all nucleated cells. Beta-2 microglobulin has a predominantly beta-folded sheet structure. In certain pathological conditions, misfolded globulin occurs, allowing amyloid fibrils to form. The encoded antimicrobial protein shows antibacterial activity in amniotic fluid.

A mutation in this gene has been shown to cause hypercatabolic hypoproteinemia.

Diseases associated with B2M include:

• immunodeficiency 43 (OMIM: 241600)
• and
• Familial visceral amyloidosis (OMIM: 105200) (see below Amyloidosis hereditary).

Associated signaling pathways include primarily interferon-gamma signaling.

The encoded protein is a component of the major histocompatibility complex(MHC) class I. It is involved in the presentation of peptide antigens to the immune system. Exogenously applied M.tuberculosis EsxA or EsxA-EsxB (or host-expressed EsxA) binds B2M and decreases its export to the cell surface (total protein concentration does not change), likely leading to defects in class I antigen presentation

1. Ardeniz O et al (2015) Beta-2-microglobulin deficiency causes a complex immunodeficiency of the innate and adaptive immune system. J Allergy Clin 0Immun 136: 392-401.
2. Waldmann TA (1969) Disorders of immunoglobulin metabolism. New Eng. J Med 281: 1170-1177.
3. Waldmann TA (1968) Hypercatabolism of IgG and albumin: a new familial disorder. (Abstract) Clin. Res 16: 45.
4. Waldmann TA et al (1990) Familial hypercatabolic hypoproteinemia: a disorder of endogenous catabolism of albumin and immunoglobulin. J Clin Invest 86: 2093-2098.
5. Wani MA et al (2006) Familial hypercatabolic hypoproteinemia caused by deficiency of the neonatal Fc receptor, FcRn, due to a mutant beta-2-microglobulin gene. Proc Nat Acad Sci 103: 5084-5089.