PhKγ2, active

Phosphorylase kinase (Phk) is a complex enzyme consisting of four different subunits, (abgd)4, and isoforms or splice variants exist for each subunit. A muscle specific form of Phk deficiency is caused by mutations in the gene for the muscle isoform of the a subunit, PHKA1, whereas liver Phk deficiency can be caused by mutations in three genes: PHKA2, PHKB, and PHKG2. PHKB mutations cause autosomal recessive Phk deficiency of both liver and muscle, but liver symptoms predominate and the biochemical muscle involvement is often not clinically apparent. Ten different mutations in the PHKB gene have been identified in seven patients. PHKG2, also autosomal, encodes the testis/liver isoform of the catalytic g subunit. PHKG2 is a serine/threonine kinase that plays an important role in glycogen metabolism. Inhibition of PHKG2 may result in recurrent hypoglycemia, liver fibrosis and increased risk of cirrhosis.