Chuvash polycythemia (MIM 263400) is an autosomal recessive disorder characterized by a high hemoglobin level, relatively high serum erythropoietin, and early death. It results from a Von Hippel-Lindau (VHL) gene mutation (C598T) that causes increased HIF-1␣ activity and erythrocyte production in the face of normoxia. This polycythemia is endemic in Chuvashia, whereas its worldwide frequency is very low. We investigated the incidence of the Chuvash-type VHL mutation in Campania (South Italy) and identified 14 affected subjects (5 families). Twelve live on the island of Ischia (Bay of Naples). From analysis of the mutated allele, we found that the disease was more frequent on Ischia (0.070) than in Chuvashia (0.057). The haplotype of all patients matched that identified in the Chuvash cluster, thereby supporting the single-founder hypothesis. We also found that nonaffected heterozygotes had increased HIF-1␣ activity, which might confer a biochemical advantage for mutation maintenance. In conclusion, we have identified the first large cluster of Chuvash erythrocytosis outside Chuvashia, which suggests that this familial polycythemia might be endemic in other regions of the world.
IntroductionThe Chuvash variant of familial polycythemia was first described in more than 100 individuals from about 80 families living in the mid-Volga River region of European Russia. 1 The disease is characterized by a high hemoglobin level, increased plasma erythropoietin (Epo) level, varicose veins, vertebral hemangiomas, low blood pressure, and an elevated serum concentration of vascular endothelial growth factor (VEGF). 2 Patients affected by Chuvash polycythemia die early, mainly as a result of cerebral vascular events or peripheral thrombosis. These injuries seem to be linked to mechanisms other than blood hyperviscosity or serum Epo content. 2 Indeed, the prevalence of low blood pressure in patients with Chuvash polycythemia contrasts with the hypertension frequently associated with polycythemia vera and other familial polycythemias resulting from excess Epo.Genome-wide screening and candidate gene characterization demonstrated that the Arg200Trp mutation (C598T) of the Von Hippel-Lindau (VHL) gene causes the Chuvash form of polycythemia. 3 Thereafter, the mutation was detected in homozygosity in patients with sporadic or familial congenital erythrocytosis from diverse ethnic groups. 4-8 However, 19 homozygotes have been identified among the more than 150 known cases of non-Chuvash familial erythrocytosis. 9 Furthermore, 8 other VHL mutations (Arg79Cys, Gly104Val, Asp126Tyr, Val130Leu, Gly144Arg, Tyr175Cys, Leu188Val, His191Asp, Pro192Ala) were detected in either homozygotes or compound heterozygotes. 4,5,7,8,10 These mutations were detected in a total of 10 cases, which indicates that the C598T transition is the major cause of VHL-related erythrocytosis.The C598T mutation likely originated from a single founder event because the VHL haplotype in non-Chuvash patients is identical to that in polycythemic patients from Chuvashia....