An inherited gain-of-function risk allele in EPOR predisposes to familial JAK2 myeloproliferative neoplasms.

Myeloproliferative neoplasms (MPN) are mainly sporadic but inherited variants have been associated with higher risk development. Here, we identified an EPOR variant (EPOR ) in a large family diagnosed with JAK2 -positive polycythaemia vera (PV) or essential thrombocytosis (ET). We investigated its functional impact on JAK2 clonal amplification in patients and found that the variant allele fraction (VAF) was low in PV progenitors but increase strongly in mature cells. Moreover, we observed that EPOR alone induced a constitutive phosphorylation of STAT5 in cell lines or primary cells. Overall, this study points for searching inherited-risk alleles affecting the JAK2/STAT pathway in MPN.