The PHKG2 gene provides instructions for making one piece, the gamma 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 gamma subunit performs the function of phosphorylase b kinase enzyme, and the other subunits help regulate its activity. 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 gamma-2 subunit produced from the PHKG2 gene is part of the enzyme found in the liver.
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 to maintain normal levels of glucose in the blood between meals. 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.
Health Conditions Related to Genetic Changes
Glycogen storage disease type IX
At least 30 mutations in the PHKG2 gene are known to cause a form of glycogen storage disease type IX (GSD IX) called GSD IXc. This form of the disorder affects liver function and causes an enlarged liver (hepatomegaly), slow growth, and periods of low blood sugar (hypoglycemia) in affected individuals. These features usually improve over time. However, PHKG2 gene mutations have been associated with more severe signs and symptoms such as irreversible liver disease (cirrhosis).
Mutations in the PHKG2 gene reduce the activity of phosphorylase b kinase in liver 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 causes the features of GSD IXc.More About This Health Condition
Other Names for This Gene
- phosphorylase b kinase gamma catalytic chain, testis/liver isoform
- phosphorylase kinase gamma subunit 2
- phosphorylase kinase subunit gamma-2
- phosphorylase kinase, gamma 2 (testis)
- phosphorylase kinase, gamma 2 (testis/liver)
- serine/threonine-protein kinase PHKG2
Additional Information & Resources
Tests Listed in the Genetic Testing Registry
Scientific Articles on PubMed
Catalog of Genes and Diseases from OMIM
- Bali DS, Goldstein JL, Fredrickson K, Rehder C, Boney A, Austin S, Weinstein DA, Lutz R, Boneh A, Kishnani PS. Variability of disease spectrum in children with liver phosphorylase kinase deficiency caused by mutations in the PHKG2 gene. Mol Genet Metab. 2014 Mar;111(3):309-313. doi: 10.1016/j.ymgme.2013.12.008. Epub 2013 Dec 19. Citation on PubMed or Free article on PubMed Central
- Brushia RJ, Walsh DA. Phosphorylase kinase: the complexity of its regulation is reflected in the complexity of its structure. Front Biosci. 1999 Sep 15;4:D618-41. Review. Citation on PubMed
- Burwinkel B, Rootwelt T, Kvittingen EA, Chakraborty PK, Kilimann MW. Severe phenotype of phosphorylase kinase-deficient liver glycogenosis with mutations in the PHKG2 gene. Pediatr Res. 2003 Dec;54(6):834-9. Epub 2003 Aug 20. Citation on PubMed
- Burwinkel B, Shiomi S, Al Zaben A, Kilimann MW. Liver glycogenosis due to phosphorylase kinase deficiency: PHKG2 gene structure and mutations associated with cirrhosis. Hum Mol Genet. 1998 Jan;7(1):149-54. Citation on PubMed
- Maichele AJ, Burwinkel B, Maire I, Søvik O, Kilimann MW. Mutations in the testis/liver isoform of the phosphorylase kinase gamma subunit (PHKG2) cause autosomal liver glycogenosis in the gsd rat and in humans. Nat Genet. 1996 Nov;14(3):337-40. Citation on PubMed