It is plausible that individuals with SVT who carry the JAK2 V617F mutation but do not exhibit obvious clinical manifestations of myeloproliferative neoplasms may represent a unique MPN subtype or an early stage of the disease, and these SVTs may manifest during the early phase of MPNs, preceding the development of overt clinical characteristics. The gene discussed is JAK2; the disease is myeloproliferative disorder.