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


Reviewed September 2008

What is the official name of the HEXB gene?

The official name of this gene is “hexosaminidase subunit beta.”

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

What is the normal function of the HEXB gene?

The HEXB gene provides instructions for making a protein that is a part (subunit) of two related enzymes, beta-hexosaminidase A and beta-hexosaminidase B. Each of these enzymes is made up of two subunits. Beta-hexosaminidase A includes one alpha subunit (produced from the HEXA gene) and one beta subunit (produced from the HEXB gene). Beta-hexosaminidase B is composed of two beta subunits, which are produced from the HEXB gene.

Beta-hexosaminidase A and beta-hexosaminidase B play a critical role in the brain and spinal cord (central nervous system). These enzymes are found in lysosomes, which are structures in cells that break down toxic substances and act as recycling centers. Within lysosomes, the enzymes break down fatty compounds called sphingolipids, complex sugars called oligosaccharides, and molecules that are linked to sugars (such as glycoproteins). In particular, beta-hexosaminidase A forms part of a complex that breaks down a fatty substance called GM2 ganglioside.

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

Sandhoff disease - caused by mutations in the HEXB gene

About 30 mutations that cause Sandhoff disease have been identified in the HEXB gene. These mutations reduce or eliminate the activity of both beta-hexosaminidase A and beta-hexosaminidase B. The malfunctioning or missing enzymes are unable to break down GM2 ganglioside and other molecules, which allows these compounds to accumulate within cells. Increased levels of GM2 ganglioside are particularly toxic to nerve cells in the central nervous system. Excess GM2 ganglioside leads to the progressive destruction of these cells, which causes many of the characteristic features of Sandhoff disease.

Most of the known mutations in the HEXB gene cause the severe form of Sandhoff disease, which becomes apparent in infancy. These mutations prevent cells from making any beta-hexosaminidase A or beta-hexosaminidase B, or lead to the production of completely nonfunctional versions of these enzymes. The most common mutation deletes a large segment of DNA near the beginning of the HEXB gene, which results in a total loss of enzyme activity. Other mutations reduce but do not eliminate the activity of the enzymes; these genetic changes are responsible for the less severe forms of Sandhoff disease, which appear later in life.

Where is the HEXB gene located?

Cytogenetic Location: 5q13

Molecular Location on chromosome 5: base pairs 74,640,023 to 74,721,288

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

The HEXB gene is located on the long (q) arm of chromosome 5 at position 13.

The HEXB gene is located on the long (q) arm of chromosome 5 at position 13.

More precisely, the HEXB gene is located from base pair 74,640,023 to base pair 74,721,288 on chromosome 5.

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

Where can I find additional information about HEXB?

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

  • beta-N-acetylhexosaminidase B
  • ENC-1AS
  • Hex B
  • hexosaminidase B
  • hexosaminidase B (beta polypeptide)

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

What glossary definitions help with understanding HEXB?

central nervous system ; DNA ; enzyme ; gene ; glycoproteins ; mutation ; nervous system ; oligosaccharides ; protein ; subunit ; toxic

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


  • Lemieux MJ, Mark BL, Cherney MM, Withers SG, Mahuran DJ, James MN. Crystallographic structure of human beta-hexosaminidase A: interpretation of Tay-Sachs mutations and loss of GM2 ganglioside hydrolysis. J Mol Biol. 2006 Jun 16;359(4):913-29. Epub 2006 Apr 27. (
  • Mahuran DJ. Biochemical consequences of mutations causing the GM2 gangliosidoses. Biochim Biophys Acta. 1999 Oct 8;1455(2-3):105-38. Review. (
  • Maier T, Strater N, Schuette CG, Klingenstein R, Sandhoff K, Saenger W. The X-ray crystal structure of human beta-hexosaminidase B provides new insights into Sandhoff disease. J Mol Biol. 2003 May 2;328(3):669-81. (
  • Mark BL, Mahuran DJ, Cherney MM, Zhao D, Knapp S, James MN. Crystal structure of human beta-hexosaminidase B: understanding the molecular basis of Sandhoff and Tay-Sachs disease. J Mol Biol. 2003 Apr 11;327(5):1093-109. (
  • Myerowitz R, Lawson D, Mizukami H, Mi Y, Tifft CJ, Proia RL. Molecular pathophysiology in Tay-Sachs and Sandhoff diseases as revealed by gene expression profiling. Hum Mol Genet. 2002 May 15;11(11):1343-50. (
  • NCBI Gene (


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: September 2008
Published: February 1, 2016