Comments on: “Clinical, hematological and genetic data of a cohort of children with hemoglobin SD”☆

Sickle cell disease (SCD) is a group of genetic conditions related to the presence of a sickle hemoglobin (Hb S) mutation (HBB:c.20A>T). People with SCD can be homozygous for Hb S or can have compound heterozygosity for Hb S with other gene mutations.1,2 Some hematologic features of SCD are listed in Table 1, but rare genotypes can also be found. Since the concentration of Hb S is a pathophysiological factor of disease severity, the presence of lower concentrations of Hb S due to double heterozygosity can determine phenotypic heterogeneity.1,3 However, other genetic and environmental factors can also have an effect on the disease phenotype.4 Studies looking for abnormal hemoglobins (Hbs) in the Brazilian population have been performed since the 1950s.5–8 However, the Brazilian Government Directive MS # 822/01 that regulates newborn screening for hemoglobinopathies, has promoted an increase of data about hemoglobinopathies in different Brazilian regions.9–11 This associated with the use of isoelectric focusing electrophoresis (IEF) and high-pressure liquid chromatography (HPLC) as diagnostic methods, has enabled the identification of an increasing number of abnormal Hbs as well as compound heterozygous states of Hb S.12–14 An example is a paper published in this issue of the Revista Brasileira de Hematologia e Hemoterapia that shows data on a cohort of children with hemoglobin SD pattern.15 Hb D is an abnormal Hb, which migrates to the same position as Hb S in electrophoresis at alkaline pH, and can be separated from Hb S in acid pH.16–18 Several Hb D have been described in different racial groups, but the majority presented a point mutation in codon 121 of the -globin gene, which results in the substitution of glutamic acid for