Congenital Erythrocytosis (CE), also called congenital polycythemia, represents a rare and heterogeneous clinical entity. It is caused by deregulated red blood cell production where erythrocyte overproduction results in elevated hemoglobin and hematocrit levels. 3Primary congenital familial erythrocytosis is associated with low erythropoietin (Epo) levels and generally results from mutations in the erythropoietin-receptor gene (EPOR).Secondary congenital erythrocytosis arises from conditions which cause tissue hypoxia thus resulting in increased Epo production. These include hemoglobin variants with increased affinity for oxygen (genes HBB, HBA1 and HBA2), decreased production of 2,3-biphosphoglycerate due to mutations in the BPGM gene, or mutations in the genes involved in the hypoxia sensing pathway (VHL, EPAS1 and EGLN1). Depending on the affected gene CE can be inherited either in an autosomal dominant or recessive mode, with sporadic cases arising de novo.Despite recent important discoveries in the molecular pathogenesis of CE, the molecular causes remain to be identified in about 70% of the patients.With the objective of collecting all the published and unpublished cases of CE the COST action MPN&MPNr-Euronet developed a comprehensive internet-based database focusing on the registration of clinical history, hematological, biochemical and molecular data (http://www.erythrocytosis.org/). In addition, unreported mutations are also curated in the corresponding Leiden Open Variation Database (LOVD).
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.
Reliable and accurate epidemiological data is a prerequisite for a cost effective screening program for inherited disorders, which however, is lacking in a number of developing countries. Here we report the first detailed population study in the Republic of Guinea, a sub-Saharan West African country, designed to assess the frequency of glucose-6-phosphate dehydrogenase (G6PD) deficiency and hemoglobinopathies, including screening for thalassemia. Peripheral blood samples from 187 Guinean adults were screened for hemoglobin (Hb) variants by standard hematological methods. One hundred and ten samples from males were screened for G6PD deficiency by the fluorescent spot test. Molecular analysis was performed for the most common α-thalassemia (α-thal) deletions, β-globin gene mutations, G6PD variants B (376A), A (376G), A- (376G/202A) and Betica (376G/968C), using polymerase chain reaction (PCR), restriction fragment length polymorphism (RFLP) or sequencing. Of the 187 subjects screened, 36 were heterozygous for Hb S [β6(A3)Glu→Val, GAG>GTG] (allele frequency 9.62%). Sixty-four subjects were heterozygous and seven were homozygous for the -α(3.7) kb deletion (allele frequency 20.85%). β-Thalassemia alleles were detected in five subjects, four with the -29 (A>G) mutation (allele frequency 1.07%) and one with codon 15 (TGG>TAG) (allele frequency 0.96%). The G6PD A- and G6PD Betica deficient variants were highly prevalent with a frequency of 5.7 and 3.3%, respectively. While we did not test for ferritin levels or α(0)-thal, four females (5.2%) had red cell indices strongly suggestive of iron deficient anemia: Hb <9.7 g/dL; MCH <19.3 pg; MCV <68.2; MCHC <31.6 g/dl; RDW >19.8%. Our results are consistent with high frequency of alleles such as Hb S, α-thal and G6PD deficient alleles associated with malaria resistance. Finding a 9.6% Hb S allele frequency supports the notion for a proficient neonatal screening to identify the sickle cell patients, who might benefit from early prophylactic treatment for infections. The incidence of significant iron deficient anemia in women is lower than expected in an under developed country.
Three major loci have been associated with HbF levels, including -158C/T (XmnI) at HBG2 promoter region, and several polymorphisms at BCL11A intron-2 and HBS1L-MYB (HMIP) intergenic region. Mutations in the KLF1 gene were recently associated with increased HbF levels. This study aims to evaluate whether genetic variability at these loci influence HbF levels in β-thalassemia carriers and in normal individuals of Portuguese origin. Sixty five β-thalassemia carriers, HbF levels ranging from 0.2% to 9.5%, and 60 individuals with normal haematological parameters, HbF levels ranging from 0.2% to 7.4%, were selected for this study. In β-thal carriers linear regression models revealed strong statistical significant association for HBG2 (XmnI) rs7482144 (β=0.45; P=5.85x10 -7 ), and nominal significance for BCL11A rs766432 (β=0.21; P=0.02) and HMIP rs9399137 (β=0.20; P=0.01). In normal individuals, a case (HbF>2%; n=15) vs. control (HbF<1.7%; n=45) model, showed nominal significant associations for BCL11A SNPs rs11886868 (OR=4; P=0.001), rs766432 (OR=3.7; P=0.002) and rs7606173 (OR=0.36; P=0.03). KLF1 rs3817621 was not found associated with HbF levels. Our results suggest that in Portuguese β-thal carriers the HBG2 XmnI polymorphism is strongly associated with HbF levels. In normal individuals, BCL11A polymorphisms, but not HMIP or HBG2 (XmnI) loci, are nominally associated with HbF expression.3
Glucose-6-phosphate isomerase (GPI) deficiency cause hereditary nonspherocytic hemolytic anemia (HNSHA) of variable severity in individuals homozygous or compound heterozygous for mutations in GPI gene. This work presents clinical features and genotypic results of two patients of Portuguese origin with GPI deficiency. The patients suffer from a mild hemolytic anemia (Hb levels ranging from 10 to 12.7g/mL) associated with macrocytosis, reticulocytosis, hyperbilirubinemia, hyperferritinemia and slight splenomegaly. Genomic DNA sequencing revealed in one patient homozygosity for a new missense mutation in exon 3, c.260G>C (p.Gly87Ala), and in the second patient compound heterozygosity for the same missense mutation (p.Gly87Ala), along with a frameshift mutation resulting from a single nucleotide deletion in exon 14, c.1238delA (p.Gln413Arg fs*24). Mutation p.Gln413Arg fs*24 is the first frameshift null mutation to be described in GPI deficiency. Molecular modeling suggests that the structural change induced by the p.Gly87Ala pathogenic variant has direct impact in the structural arrangement of the region close to the active site of the enzyme.
Neonatal cyanosis in healthy newborns can be associated either with methemoglobin due to cytochrome b5 reductase deficiency or to M-Hemoglobin, a group of hemoglobin variants resulting from mutations in the globin chain genes. We report the clinical case of a neonate with cyanosis and normal cardiac and respiratory function. At birth the hematological parameters were normal; however the methemoglobinemia was 16%. Spontaneously the cyanosis gradually decreased and by the fifth month of age the methemoglobin level wasnormal. An heterozygous G globin gene (HBG2) missense mutation 87 C-A (Leu28Met) was identified. His father, with a past history of transfusion in the neonatal period, is heterozygous for the same mutation. This hemoglobin variant, not previously described, was called Hb-FViseu and is the sixth G gamma chain variant reported in association with neonatal cyanosis.
Glucose-6-phosphate dehydrogenase (G6PD) deficiency, an X-linked disorder, is usually observed in hemizygote males and very rarely in females. The G6PD class 1 variants, very uncommon, are associated with chronic hemolytic anemia. Here we report a Portuguese woman who suffered in her sixties from a chronic hemolytic anemia due to G6PD deficiency. Molecular studies revealed heterozygosity for an in-frame 18-bp deletion, mapping to exon 10 leading to a deletion of 6 residues, 362-367 (LNERKA), which is a novel G6PD class 1 variant, G6PD Tondela. Two of her three daughters, asymptomatic, with G6PD activity within the normal range, are heterozygous for the same deletion. The patient's leukocyte and reticulocyte mRNA studies revealed an almost exclusive expression of the mutant allele, explaining the chronic hemolytic anemia. Patient whole blood genomic DNA HUMARA assay showed a balanced pattern of X chromosome inactivation (XCI), but granulocyte DNA showed extensive skewing, harboring the mutated allele, implying that in whole blood, lymphocyte DNA, with a very long lifetime, may cover up the current high XCI skewing. This observation indicates that HUMARA assay in women should be assessed in granulocytes and not in total leukocytes. © 2011 Elsevier Inc. All rights reserved. IntroductionX chromosome inactivation (XCI) is an epigenetic process, unique in mammals, by which one of the two X chromosomes in each cell is inactivated in females early in embryogenesis [1]. Therefore, women are a mosaic of paternal and maternal active X chromosome and a theoretical 1:1 ratio of two cell lines with inactive maternal to paternal X chromosome could be expected. The XCI ratio is usually assessed analyzing protein variants directly in heterozygous females' cells [2], transcribed mRNA expression [3] or DNA methylation status of polymorphic X-linked genes, such as the human androgen receptor (HUMARA) gene [4]. Deviation from the theoretical 1:1 ratio between the 2 parental alleles is called skewing. Several reports using the HUMARA assay show that the incidence of skewing is relatively low at birth and in adult non-hematopoietic tissues, but higher and agedependent in hematopoietic cells, with 30-40% of healthy elderly women reported to have skewing (greater than 75% expression of one parental X chromosome) [5][6][7][8][9][10][11][12]. T lymphocytes show less evidence of skewing with age than neutrophils, presumably reflecting the neutrophils' short half-life, whereas T lymphocytes are long-living cells, and in consequence, some T cells are produced near the time of study but others are derived from earlier stem cells [11][12][13]. This agerelated skewing in blood cells has been attributed to clonality as a consequence of hematopoietic stem cell senescence [5,7,9]. Swierczek et al. report a discrepancy between the skewed XCI observed in blood cells of 45 elderly women (ages 65-92 years; mean, 81.3 years) using the methylation-based HUMARA assay and a transcriptional based assay: with HUMARA assay in granulocyte DNA they found an ag...
This study confirmed the presence of Q248H mutation at polymorphic frequencies in three native sub-Saharan populations. Analysis of two additional markers in the same gene support a single origin of the mutant allele c.744T in the haplotype background IVS1( - 24)G/(CGG)(7).
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