RESUMEN

Fetal hemoglobin is a major genetic modifier of the phenotypic heterogeneity in patients with sickle cell disease and certain ß-thalassemias. Normal levels of fetal hemoglobin postnatally are approximately 1% of total hemoglobin. Patients who have hereditary persistence of fetal hemoglobin, characterized by elevated synthesis of γ-globin in adulthood, show reduced disease pathophysiology. Hereditary persistence of fetal hemoglobin is caused by ß-globin locus deletions (deletional hereditary persistence of fetal hemoglobin) or γ-globin gene promoter point mutations (non-deletional hereditary persistence of fetal hemoglobin). Current research has focused on elucidating the pathways involved in the maintenance/reactivation of γ-globin in adult life. To better understand these pathways, we generated new ß-globin locus yeast artificial chromosome transgenic mice bearing the (A)γ-globin -175 T > C or -195 C > G hereditary persistence of fetal hemoglobin mutations to model naturally occurring hereditary persistence of fetal hemoglobin. Adult -175 and -195 mutant ß-YAC mice displayed a hereditary persistence of fetal hemoglobin phenotype, as measured at the mRNA and protein levels. The molecular basis for these phenotypes was examined by chromatin immunoprecipitation of transcription factor/co-factor binding, including YY1, PAX1, TAL1, LMO2, and LDB1. In -175 HPFH versus wild-type samples, the occupancy of LMO2, TAL1 and LDB1 proteins was enriched in HPFH mice (5.8-fold, 5.2-fold and 2.7-fold, respectively), a result that concurs with a recent study in cell lines showing that these proteins form a complex with GATA-1 to mediate long-range interactions between the locus control region and the (A)γ-globin gene. Both hereditary persistence of fetal hemoglobin mutations result in a gain of (A)γ-globin activation, in contrast to other hereditary persistence of fetal hemoglobin mutations that result in a loss of repression. The mice provide additional tools to study γ-globin gene expression and may reveal new targets for selectively activating fetal hemoglobin.

Asunto(s)

RESUMEN

Sickle cell anemia is a genetic disease with high prevalence in people of African descent. There are five typical haplotypes associated with this disease and the haplotypes associated with the beta-globin gene cluster have been used to establish the origin of African-descendant people in America. In this work, we determined the frequency and the origin of haplotypes associated with hemoglobin S in a sample of individuals with sickle cell anemia (HbSS) and sickle cell hemoglobin trait (HbAS) in coastal regions of Colombia. Blood samples from 71 HbAS and 79 HbSS individuals were obtained. Haplotypes were determined based on the presence of variable restriction sites within the ß-globin gene cluster. On the Pacific coast of Colombia the most frequent haplotype was Benin, while on the Atlantic coast Bantu was marginally higher than Benin. Eight atypical haplotypes were observed on both coasts, being more diverse in the Atlantic than in the Pacific region. These results suggest a differential settlement of the coasts, dependent on where slaves were brought from, either from the Gulf of Guinea or from Angola, where the haplotype distributions are similar. Atypical haplotypes probably originated from point mutations that lost or gained a restriction site and/or by recombination events.

RESUMEN

Las hemoglobinas inestables son variantes estructurales de lamolécula de hemoglobina originadas, en su mayoría, por sustitucionespuntuales de aminoácidos en alguna de las cadenas de globina. Estos cambios afectan la estabilidad de la molécula,causan pérdida de la solubilidad y precipitación dentro del eritrocito, lo cual provoca su destrucción acelerada. Desde el punto de vista clínico, las hemoglobinas inestables puedenpresentar anemia hemolítica crónica de gravedad variable.La hemoglobina Evans es una hemoglobina inestable causadapor la sustitución de valina por metionina en la posición 62 de la cadena de alfa globina. Hemos identificado esta variante en una niña con crisis hemolítica aguda asociada a faringitis y en dos miembros de su grupo familiar. Éste es el tercer caso de anemia hemolítica congénita causada por hemoglobina Evans comunicado en la bibliografía mundial.

Unstable hemoglobins are structural variants of the hemoglobin molecule, mostly originated by single amino-acid replacement in some globin chains. These changes affect molecule stability, leading to loss of solubility, precipitation, and cellular lysis. Patients carrying these unstable hemoglobins may present mild to severe chronic hemolytic anemia. Hemoglobin Evans is an unstable variant originated by replacement of valine with methionine at position 62 of the αa-globin chain. We have identified this variant in a girl with an acute hemolytic crisis associated to pharyngitis, as well as in two of her family members. This is the third case of hemolytic anemia due to hemoglobin Evans reported in the literature.

Asunto(s)

RESUMEN

Methemoglobin (Hb-M) is a rare hemoglobinopathy in China. We hereby report on a family living in Yantai, East China, with congenital cyanosis due to Hb-M mutation. The proband, a 65-year-old female, presented 63% oxygen saturation. Both Hb-M concentration and arterial oxygen saturation remained unchanged, even following intravenous treatment with methylene blue. There was also no change in blood-color (chocolate-brown) after adding 0.1% KCN. A fast-moving band (Hb-X) in hemolysates was found by cellulose acetate electrophoresis, the Hb-X/Hb-A ratio exceeding 10%. GT transition at 131nt of exon 2, although present in one of the α(2) -globin alleles, was not found in α(1) -globin alleles as a whole. This mutation leads to the aspartic acid to tyrosine substitution (Asp76Tyr). In this family, the novel mutation in the α(2) -globin gene resulted in a rare form of congenital cyanosis due to Hb-M. This hemoglobin was named Hb-M (Yantai) .

RESUMEN

Methemoglobin (Hb-M) is a rare hemoglobinopathy in China. We hereby report on a family living in Yantai, East China, with congenital cyanosis due to Hb-M mutation. The proband, a 65-year-old female, presented 63 percent oxygen saturation. Both Hb-M concentration and arterial oxygen saturation remained unchanged, even following intravenous treatment with methylene blue. There was also no change in blood-color (chocolate-brown) after adding 0.1 percent KCN. A fast-moving band (Hb-X) in hemolysates was found by cellulose acetate electrophoresis, the Hb-X/Hb-A ratio exceeding 10 percent. GT transition at 131nt of exon 2, although present in one of the alfa2-globin alleles, was not found in alfa1-globin alleles as a whole. This mutation leads to the aspartic acid to tyrosine substitution (Asp76Tyr). In this family, the novel mutation in the alfa2-globin gene resulted in a rare form of congenital cyanosis due to Hb-M. This hemoglobin was named Hb-M Yantai.

Asunto(s)

RESUMEN

The fetal hemoglobin (HbF) levels and betaS-globin gene haplotypes of 125 sickle cell anemia patients from Brazil were investigated. We sequenced the Gg- and Ag-globin gene promoters and the DNase I-2 hypersensitive sites in the locus control regions (HS2-LCR) of patients with HbF level disparities as compared to their ßS haplotypes. Sixty-four (51.2 percent) patients had CAR/Ben genotype; 36 (28.8 percent) Ben/Ben; 18 (14.4 percent) CAR/CAR; 2 (1.6 percent) CAR/Atypical; 2 (1.6 percent) Ben/Cam; 1 (0.8 percent) CAR/Cam; 1 (0.8 percent) CAR/Arab-Indian, and 1 (0.8 percent) Sen/Atypical. The HS2-LCR sequence analyses demonstrated a c.-10.677G>A change in patients with the Ben haplotype and high HbF levels. The Gg gene promoter sequence analyses showed a c.-157T>C substitution shared by all patients, and a c.-222_-225del related to the Cam haplotype. These results identify new polymorphisms in the HS2-LCR and Gg-globin gene promoter. Further studies are required to determine the correlation between HbF synthesis and the clinical profile of sickle cell anemia patients.

Asunto(s)

RESUMEN

Beta S-globin gene (âS-globin) haplotypes, markers for severe sickle cell anemia (SCA), and the alpha-thalassemia 2 gene 3.7 kb deletion (-á2(3.7 kb) thal) along with demographic and clinical data were investigated in SCA outpatients (n = 125, 63 female and 62 male) in the Brazilian state of Bahia, which has a high prevalence SCA. PCR-RFLP showed that the Central African Republic/Benin (CAR/BEN, 51.2 percent) haplotype was most frequent, followed by the Benin/Benin (Ben/Ben, 28.8 percent). At least one CAR haplotype was present in every outpatient with a history of cerebrovascular accident. The Cameroon (Cam), Senegal (Sen) and Arab-India haplotypes occurred in small numbers, as did atypical haplotypes. Fetal hemoglobin (HbF, percent) was unevenly distributed. Compared to those > 18 y, those aged < 18 y had had fewer erythrocyte transfusions and high HbF levels (12.3 percent ± 7.01 to 7.9 percent ± 4.36) but a higher frequency of spleen sequestration and pneumonia. Compared with normal á - genes carriers values, the outpatients with -á2(3.7 kb) thal (determined by PCR analysis) had significantly higher mean hemoglobin concentration (Hb) (8.3 ± 1.34 g/dL, p = 0.018) and packed cell volume (PCV = 27.1 percent ± 4.26, p = 0.019) but low mean corpuscular volume (MCV = 86.1 fL = 10-15 L ± 9.56, p = 0.0004) and mean corpuscular hemoglobin (MCH = 26.6 percent ± 4.60, p = 0.039).