Thirty-six unrelated cases with erythrocytosis of unknown origin were investigated. Exons 5-8 of the erythropoietin receptor gene (EPOR), the von Hippel-Lindau gene, and the prolyl hydroxylase domain protein 2 gene (PHD2) were screened by direct DNA sequencing. The Janus kinase 2 mutation, JAK2 (Val617Phe), was screened by allele specific PCR. In this study, three new mutations of EPOR causing deletions in exon 8 were found: the first led directly to a stop codon [g.5957_5958delTT (p.Phe424X)], the second to a stop codon after one residue [g.5828_5829delCC (p.Pro381GlnfsX1)] and the third to a stop codon following a frameshift sequence of 23 residues [g.5971delC (p.Leu429TrpfsX23)]. One patient had a previously reported EPOR mutation [g.6146A>G (p.Asn487Ser)] and another, a silent one (g.5799G>A). All were heterozygotes. In addition, 2 patients were positive for JAK2 (Val617Phe), and 2 reported elsewhere, were mutated in the PHD2 gene [c.606delG (p.Met202IlefsX71).

In a family of Spanish origin, five individuals presented a heterozygous alpha(0)-thalassemia (alpha-thal)-like phenotype. All had a -alpha(3.7) deletion with the recombinant alpha gene carrying the Hb Suan-Dok [alpha109(G16)LeuArg] mutation, proposed to be thalassemic. Thus, the abnormal chromosome carried an alpha(0)-thal-like allele that has to be taken into account for genetic counseling and prenatal diagnosis. The possibility of Hb H disease or hydrops fetalis should be considered when this allele is associated with alpha(+)-thal or with another alpha(0)-thal, respectively. Other described genotypes associated with Hb Suan-Dok are discussed.

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