Sequenciamento genético e pesquisa de α-talassemia das hemoglobinas variantes de comportamento físico-químico semelhante ao da hemoglobina S (S-like) em crianças do Programa Nacional de Triagem Neonatal do estado do Rio de Janeiro

Abstract

Brazilian population is characterized by having a unique genetic composition which is a result of its intense miscegenation throughout history. Genetic recombination resulting from this process can lead to diseases such as hemoglobinopathies. Some hemoglobin variants have physical-chemical behavior similar to the Hb S and are referred as S-like. These molecules can lead to a false diagnosis of sickle cell trait and are usually asymptomatic, however when in combination with other hemoglobinopathies and thalassemias they may represent important hematological alterations and critical clinical conditions. This study aimed to identify by genetic sequencing S-like hemoglobins of Rio de Janeiro Newborn Screening Program, and to verify the association of these variants with alpha thalassemia. For the purpose of this study, 17 blood samples of newborns were selected from October, 22, 2010 to February 1, 2017, which presented in their investigation hemoglobinopathies, hemoglobin variants in S-Window, by the methodology HPLC ) - ULTRA 2™ with the Genesys Ultra Screening Kit (Trinity Biotech, Jamestown, NY). They were submitted by molecular analysis through PCR to verify the presence of alpha thalassemia and genetic sequencing of alpha (HBA) and beta chains of the hemoglobin (HBB). The HPLC-VARIANT® technique with the β-Thalassemia Short kit (Bio-Rad, California, USA) was performed to reassess the hemoglobin profile. Chromatograms revealed characteristic profiles of 4 Hb Stanleyville II, 5 Hb D-Punjab, 5 Hb Korle-Bu, 1 Hb Constant Spring and 2 undefined variants. The molecular analysis showed that 8 samples (47.05%) had the -α3.7/αα deletion. The sequencing of the alpha gene performed on 3 samples revealed the presence of Hb Stanleyville II, however with the mutation present in the -α3.7 hybrid gene, unlike most cases described in the literature. In the beta globin gene, the polymorphisms found were the same for the three samples sequenced: one in the first exon and two in the second intron. In conclusion, Hb Stanleyville II, D-Punjab and Korle-Bu although not frequent, in the state of Rio de Janeiro are not uncommon. The association between -α3.7 and the S-like variants found in the research is frequent. The study of HBB and HBA genes by sequencing methodology is necessary to identify new mutations and to confirm the diagnoses of more complex hemoglobinopathies. The mutation of Hb Stanleyville II corresponding to codon 78 at the third baseline (AAC> AAA) in the hybrid gene -α3.7 is uncommon and appears to be the second case described in Brazil.