A somatic mutation, V617F, affecting the Janus tyrosine kinase 2 (JAK2) gene acts as a disease specific molecular marker which is used along with other tests such as erythropoietin for diagnosis of myeloproliferative neoplasms (MPNs), a bone marrow disorder which lead to overproduction of blood cells. The MPNs most commonly associated with JAK2 mutation are: polycythemia vera (PV), essential

thrombocythemia (ET) and primary myelofibrosis (PMF), also known as chronic idiopathic myelofibrosis or agnogenic myeloid metaplasia.

JAK2 V617F is a point mutation at a specific location (nucleotide G1849T) in the JAK2 gene and is the primary genetic test for JAK2 mutations leading to MPNs. This change results in a JAK2 protein that is constantly “on,” leading to uncontrolled blood cell growth. JAK2 V617F is a gain-of-function mutation that leads to clonal proliferation; it is present in about 95% of PV cases and about 50% of ET and MF cases.

Since 2008,diagnostic criteria for ET, MF, and PV adopted by the World Health Organization (WHO) has been revised and include identification of mutation marker adding the presence of JAK2 mutation as a major criterion for diagnostic confirmation for the diagnosis of BCR- ABL negative MPN.