Hereditary erythrocytosis has instead been linked with germline EPOR GOF mutations that lead to truncations of the encoded EPO-R that serve to enhance sensitivity to EPO [50], as well as various other germline mutations (including EPO GOF mutations and loss-of-function (LOF) mutations in the VHL gene encoding a key regulator) that serve to increase transcription of the EPO gene, resulting in high levels of EPO protein [51]. This evidence concerns the gene EPO and polycythemia.