IntroductionCongenital Erythrocytosis can be classified as primary, when the defect is intrinsic to the RBC progenitors and independent of the serum erythropoietin (Epo) concentration, or secondary, when the erythrocytosis is the result of an up-regulation of Epo production. Primary erythrocytosis is associated with mutations in the EPOR gene, secondary congenital erythrocytosis can de due to mutations that stabilize the hemoglobin in the oxygenated form or to mutations in the genes that control the transcriptional activation of the EPO gene -VHL, EGLN1, EPAS1. Material and MethodsWith the main objective of describing the etiology and molecular basis of congenital erythrocytosis we have studied 70 consecutive unrelated patients presenting with idiopathic erythrocytosis from our hematology clinic or referred from other centers. According to a study algorithm we have sequenced all the genes described as associated with congenital erythrocytosis. Results and DiscussionErythrocytosis molecular etiology was identify in 25 (36%) of the 70 subjects. High-affinity Hb variants were the most common cause, present in 20% of the cases. New mutations were identified in the JAK2, EPOR, VHL and EGLN1 genes. Conclusions High affinity hemoglobin variants are a very rare cause of secondary congenital erythrocytosis, but it seems likely that their incidence may be underestimated. Our experience shows that in erythrocytosis with a dominant inheritance and normal or inappropriate high Epo levels, the HBB and HBA genes should be the first to be studied. In spite of the seven genes known to be involved in congenital erythrocytosis, the majority of the cases have unknown etiology.

A fixed dose of 300 μg of darbepoetin alfa weekly (with or without filgrastim) seems to be an effective and safe treatment for anemic patients with low or intermediate-risk MDS, low transfusion burden and EPO levels <500 IU/L. Results may not be extrapolable to unselected MDS patients.

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We report a new structural defect of the α2-globin chain presenting with moderate microcytic hypochromic anemia, in six individuals from three unrelated families, living in Portugal and Spain. α-Globin gene deletions were ruled out by gap-polymerase chain reaction (gap-PCR) and multiplex ligation-dependent probe amplification (MLPA). Direct sequencing of the α2-globin gene revealed a substitution of codon 104 [α104(G11)Cys→Arg, TGC>CGC (α2) (HBA2:c.313T>C)]. This new variant, not detectable by high performance liquid chromatography (HPLC) or electrophoresis, was called Hb Iberia, as it was observed for the first time in families from the Iberian Peninsula. Although the mutant allele is transcribed, as indicated by the balanced mRNA α/β ratio, the abnormal α2 chain could not form a stable tetramer as the cysteine and arginine residues, located at the α1β1 contact, differ in size, charge and hydrophobicity. Hb Iberia is the third mutation described at codon 104 on the α-globin genes, namely, Hb Sallanches (α2, TGC>TAC) and Hb Oegstgeest (α1, TGC>AGC), also characterized as unstable hemoglobins (Hbs), present on an α-thalassemic phenotype.

Hb La Coruña [beta38(C4)Thr --> Ile] is a new hemoglobin (Hb) variant that has an increased oxygen affinity. Clinically, this Hb leads to erythrocytosis. Hb La Coruña is an electrophoretically silent variant that can be detected by reversed phase high performance liquid chromatography (HPLC) and characterized by DNA sequencing. The patient was a 22-year-old Spanish male whose family lived in La Coruña, in the northwest of Spain. His mother was also a carrier.