JAK2 MUTATION

JAK2 Mutation — present in >95% of polycythemia vera, the JAK2 V617F mutation defines the diagnosis and unlocks JAK2 inhibitor therapy that has transformed myeloproliferative neoplasm management.

Whole genome sequencing evaluates JAK2 V617F, JAK2 exon 12 variants, and additional MPN genes (CALR, MPL) — providing comprehensive molecular evaluation for myeloproliferative neoplasm diagnosis and treatment selection.

JAK2
CALR
MPL

About this condition

JAK2 Mutation — Myeloproliferative Neoplasms

The JAK2 V617F mutation (valine to phenylalanine at position 617) is a somatic gain-of-function mutation in the Janus kinase 2 gene found in >95% of polycythemia vera (PV), 50-60% of essential thrombocythemia (ET), and 50-60% of primary myelofibrosis (PMF). Discovery of JAK2 V617F in 2005 revolutionized MPN diagnosis and treatment. The mutation activates the JAK-STAT signaling pathway constitutively, driving proliferation of myeloid cells independent of growth factor signaling.

JAK2 inhibitors have transformed MPN management. Ruxolitinib (Jakafi), the first FDA-approved JAK1/2 inhibitor (2011), produces significant improvement in splenomegaly, constitutional symptoms (night sweats, weight loss, fatigue), and quality of life in myelofibrosis and PV. Fedratinib (Inrebic) is approved for intermediate/high-risk myelofibrosis. Pacritinib (Vonjo) is approved for myelofibrosis with thrombocytopenia. These targeted therapies are available regardless of JAK2 mutation status but were developed from understanding JAK2 V617F biology.

JAK2 V617F is primarily a somatic (acquired) mutation — it arises in hematopoietic stem cells and is not inherited. However, familial predisposition to MPNs is well-documented — first-degree relatives of MPN patients have 5-7x increased risk. Germline variants in JAK2 (46/1 haplotype), TERT, and other genes predispose to somatic MPN development. A rare germline JAK2 V617I variant causes hereditary erythrocytosis. WGS evaluates both somatic MPN mutations (when performed on blood) and germline predisposition variants.

JAK2 V617F is primarily somatic (acquired), but familial MPN clustering is real — first-degree relatives have 5-7x increased risk. The JAK2 46/1 germline haplotype predisposes to acquiring the V617F mutation.

Gene locus: JAK2 (9p24.1), CALR (19p13.13), MPL (1p34.2)

JAK2 V617F testing is central to MPN diagnosis. WGS provides JAK2 V617F detection alongside CALR, MPL, and germline MPN predisposition variants — the complete MPN molecular workup in one test.

JAK2 V617F is required for WHO PV diagnosis — and JAK2 inhibitors provide symptom relief even in V617F-negative MPNs

WHO diagnostic criteria for PV require either JAK2 V617F or exon 12 mutation. ET and PMF diagnosis uses JAK2, CALR, or MPL mutations as major criteria. WGS evaluates all three gene targets simultaneously, providing WHO-compliant molecular diagnosis. JAK2 inhibitors (ruxolitinib) are effective for symptom relief regardless of molecular subtype — but molecular diagnosis is essential for accurate classification and prognosis.

JAK2 V617F allele burden correlates with disease severity and transformation risk — quantitative assessment guides prognosis

Higher JAK2 V617F allele burden (the percentage of cells carrying the mutation) correlates with increased risk of thrombosis, progression from ET to PV, and transformation to myelofibrosis or acute leukemia. Serial monitoring of allele burden can assess treatment response. WGS provides quantitative allele burden assessment alongside comprehensive molecular evaluation.

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