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The official name of this gene is “phosphorylase kinase, beta.”
PHKB is the gene's official symbol. The PHKB gene is also known by other names, listed below.
The PHKB gene provides instructions for making one piece, the beta subunit, of the phosphorylase b kinase enzyme. This enzyme is made up of 16 subunits, four each of the alpha, beta, gamma, and delta subunits. (Each subunit is produced from a different gene.) The beta subunit helps regulate the activity of phosphorylase b kinase. This enzyme is found in various tissues, although it is most abundant in the liver and muscles. One version of the enzyme is found in liver cells and another in muscle cells. The beta subunit produced from the PHKB gene is part of the enzyme found both in the liver and in muscle.
Phosphorylase b kinase plays an important role in providing energy for cells. The main source of cellular energy is a simple sugar called glucose. Glucose is stored in muscle and liver cells in a form called glycogen. Glycogen can be broken down rapidly when glucose is needed, for instance during exercise. Phosphorylase b kinase turns on (activates) another enzyme called glycogen phosphorylase b by converting it to the more active form, glycogen phosphorylase a. When active, this enzyme breaks down glycogen.
At least 14 mutations in the PHKB gene are known to cause a form of glycogen storage disease type IX (GSD IX) called GSD IXb. This form of the disorder affects the liver and the muscles. The liver problems caused by this disorder include an enlarged liver (hepatomegaly), slow growth, and periods of low blood sugar (hypoglycemia). These features usually improve over time. The condition can also cause mild muscle weakness, although some affected individuals have no muscle problems.
Mutations in the PHKB gene reduce the activity of phosphorylase b kinase in liver and muscle cells, although the mechanism is unknown. Reduction of this enzyme's function impairs glycogen breakdown. As a result, glycogen builds up in cells, and glucose is not available for energy. The inability to break down glycogen in the liver and reduced energy production in muscle cells lead to the features of GSD IXb.
Cytogenetic Location: 16q12-q13
Molecular Location on chromosome 16: base pairs 47,461,298 to 47,701,522
The PHKB gene is located on the long (q) arm of chromosome 16 between positions 12 and 13.
More precisely, the PHKB gene is located from base pair 47,461,298 to base pair 47,701,522 on chromosome 16.
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 PHKB 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.
breakdown ; enzyme ; gene ; glucose ; glycogen ; hypoglycemia ; kinase ; muscle cells ; simple sugar ; subunit
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.