JAK-2 Mutation (Exon 14, 12)

Function

The Janus Kinase 2 (JAK2) gene provides instructions for making a protein that promotes the growth and division of cells. This test looks for mutations in Exon 14 (V617F) and Exon 12. These mutations act like a 'broken switch,' keeping the JAK2 protein constantly active, which leads to the overproduction of blood cells.

Why it is Ordered

This test is crucial when a patient has a high red blood cell count (erythrocytosis), high platelets (thrombocytosis), or high white cells, and the doctor suspects a Myeloproliferative Neoplasm (MPN). It helps distinguish between a primary bone marrow disorder and a 'secondary' reaction (like high red cells due to smoking).

Associated Conditions

• Polycythemia Vera (PV): Over 95% of patients with PV have the JAK2 V617F mutation.
• Essential Thrombocythemia (ET): About 50-60% of patients carry this mutation.
• Primary Myelofibrosis (PMF): Frequently associated with JAK2 mutations.

Importance of Testing

Identifying the JAK2 mutation is a major diagnostic criterion in the WHO classification of blood cancers. It confirms that the cell proliferation is 'clonal' (cancerous) rather than a response to another condition.