(E) Bone marrow trephine stained for glycophorin C. (F) Bone marrow trephine stained for CD61. gl The elder sister was referred independently for assessment of erythrocytosis in 2020, when she was aged 48, without knowledge of her sister's history. Cooperation of germ line JAK2 mutations E846D and R1063H in hereditary erythrocytosis with megakaryocytic atypia. Mutations in the Janus-associated kinase 2 ( I JAK2 i ) gene are found at varying frequency in myeloproliferative disorders but are almost always present in true cases of polycythaemia vera (PV). Crucially, this report represents 127 patient years with no occurrence of thrombosis indicating that germline heterozygous I JAK2 i E846D substitutions are unlikely to be a strong independent risk factor for thrombosis. [Extracted from the article]