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The official name of this gene is “hexosaminidase B (beta polypeptide).”
HEXB is the gene's official symbol. The HEXB gene is also known by other names, listed below.
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.
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.
Cytogenetic Location: 5q13
Molecular Location on chromosome 5: base pairs 74,640,022 to 74,721,287
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 74,640,022 to base pair 74,721,287 on chromosome 5.
See How do geneticists indicate the location of a gene? (http://ghr.nlm.nih.gov/handbook/howgeneswork/genelocation) in the Handbook.
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.
See How are genetic conditions and genes named? (http://ghr.nlm.nih.gov/handbook/mutationsanddisorders/naming) in the Handbook.
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 (http://ghr.nlm.nih.gov/glossary).
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? (http://ghr.nlm.nih.gov/handbook/consult/findingprofessional) in the Handbook.