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PHKG2 gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

PHKG2 gene

The PHKG2 gene provides instructions for the gamma subunit of the phosphorylase b kinase enzyme, which is vital for glycogen metabolism in the liver.

Normal Function

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. The gamma subunit performs the function of the 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. 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
  • Periods of low blood glucose (hypoglycemia)

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. 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.

Other Names for This Gene

  • GSD9C
  • PHK-gamma-T
  • PHKG2_HUMAN
  • 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)
  • PSK-C3
  • serine/threonine-protein kinase PHKG2

Frequently Asked Questions

frequent, carbohydrate‑rich diet with complex carbs and small, regular meals helps maintain blood glucose. Some patients benefit from a nighttime snack or continuous glucose monitoring to prevent nocturnal hypoglycemia. Consultation with a dietitian experienced in metabolic disorders is recommended.
There is no cure, but liver‑supportive therapies such as enzyme replacement are not available. Management focuses on dietary control, monitoring liver function, and treating complications. In severe cases, liver transplantation may be considered, but most patients improve with age and proper management.
Children with PHKG2 mutations may develop an enlarged liver (hepatomegaly), poor growth, and episodes of low blood sugar (hypoglycemia) especially between meals. Parents should watch for poor weight gain, fatigue, and jaundice, and seek evaluation if these occur.
Diagnosis involves a combination of liver imaging to detect hepatomegaly, blood tests showing hypoglycemia and elevated liver enzymes, and a genetic test that sequences the PHKG2 gene to identify pathogenic variants. A liver biopsy may be done to assess glycogen accumulation.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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