Mutation in the negative regulatory element of the erythropoietin receptor gene in a case of sporadic primary polycythemia.

A 42-year-old Caucasian male with sporadic primary polycythemia has been followed by us for 13 years. During the time of observation, his hemoglobin had been stable, and he has never had an elevated white count or platelet count or any other stigmata of polycythemia vera (PV). Both of his parents, his three children, and all siblings have been hematologically normal. The in vitro culture of erythroid progenitors revealed an absence of autonomous erythropoietin (Epo)-independent erythroid colonies but demonstrated a marked increase in the sensitivity of erythroid progenitors to Epo. We have undertaken a study designed to determine whether a mutation in the Epo receptor (Epo-R) gene could cause the polycythemia phenotype seen in either dominant or recessive primary polycythemia described by us and others, or in polycythemia vera. We have sequenced the cytoplasmic positive and negative regulatory domains of the Epo-R genomic DNA, and a transversion of C to T in nucleotide 6148 was found in one of the patient's chromosomes. This mutation is located in the negative regulatory domain and results in a change from proline to serine (P488S). We have subsequently analyzed more than 40 chromosomes from unrelated normal subjects, as well as autosomal dominant, recessive, and sporadic primary polycythemia and polycythemia vera subjects. In no instance was the same or any other mutation in the Epo-R found. To determine if this Epo-R mutation is a cause of increased sensitivity of erythroid progenitors to erythropoietin, Ba/F3 cells (interleukin-3-dependent murine lymphoid line) were transfected with normal and mutated Epo-R cDNA, rendering the transfected cells viable and able to proliferate in Epo. Transfectants with wild-type and mutant Epo-R cDNA exhibited no difference in the presence of Epo. More recently, we were able to obtain DNA from the seven family members of the propositus and found that the nonpolycythemic mother and one of the siblings have the same Epo-R mutation. We conclude that this first described mutation of Epo-R encountered in humans does not appear on its own to explain the polycythemia phenotype; however, the possibility that it may interact with some other acquired or congenital abnormality in generating the polycythemia phenotype cannot be excluded.