JAK2 is a kinase that is misregulated or mutated in a number of myeloproliferative diseases and cancers. The mutation V617F is the most clinically relevant variant, and is seen in around half of myeloproliferative disorders. The variant is a known activating mutation, and activated JAK2 is sufficient to drive myeloproliferative disorders in mouse models. V617F, while most recurrent, is not the only mechanism by which JAK2 can be activated in patients. JAK2 is now one of the first diagnostic markers tested upon diagnosis with a myeloproliferative disorder. JAK3 (Janus Kinase 3) is a Protein Coding gene. Diseases associated with JAK3 include Scid, Autosomal Recessive, T-Negative/B-Positive Type and Severe Combined Immunodeficiency, B Cell-Negative. Among its related pathways are Common Cytokine Receptor Gamma-Chain Family Signaling Pathways and Th2 Differentiation Pathway. GO annotations related to this gene include transferase activity, transferring phosphorus-containing groups and protein tyrosine kinase activity. An important paralog of this gene is JAK2.