Print version ISSN 0004-282X
Arq. Neuro-Psiquiatr. vol.70 no.8 São Paulo Aug. 2012
Alfa-talassemia protege crianças com anemia falciforme contra doença cerebrovascular
André Rolim BelisárioI,II; Marina Lobato MartinsI; Cibele Velloso-RodriguesI; Célia Maria SilvaI; Marcos Borato Viana
IFoundation and Center for Hematology and Hemotherapy of Minas Gerais (HEMOMINAS), Belo Horizonte MG, Brazil
IIMedical School/Nupad, Department of Pediatrics, Federal University of Minas Gerais (UFMG), Belo Horizonte, Brazil
Cerebrovascular disease (CVD) is a severe complication in children with sickle cell anemia (SCA). Currently, transcranial Doppler (TCD) ultrasonography is the only clinical tool available to detect increased risk of occurrence of CVD in these children. TCD is a very sensitive, but moderately specific test: 60% of untreated children with abnormal velocities did not develop a stroke at 40 months1, and it would be unnecessarily subjected them to prophylactic blood transfusions. The identification of more specific biomarkers is clearly needed. Recently, Filho et al. found that Bantu/Atypical βS-globin gene cluster haplotype (βS-haplotype) was associated with the occurrence of CVD, and alpha-thalassemia (α-thal) was not2.
We also have studied the influence of βS-haplotype and α-thal on CVD in a cohort of 208 children with SCA from Minas Gerais state, Brazil, and published it in 20103,4. In our experience, α-thal genotypes were significantly associated with reduction in CVD risk4. This association has been previously described. Although the prevalence of α-thal was lower in patients with CVD in the study published by the Arquivos2, the association was not statistically significant probably because the sample was too small (n=86) to detect the difference.
In our study, the data regarding βS-haplotypes were analyzed in several ways, and none showed a significant association between haplotypes and CVD3. The only current evidence on the association between βS-haplotypes and SCA phenotype is their relationship to the level of Hb F. However, the Hb F concentration seems to have no association with CVD5.
We would like to know whether some analyses were done for this population and were not shown in the study:
Were the patients molecularly tested to confirm sickle cell genotypes? Maybe some βº-thalassemic chromosomes were misclassified as atypical βS-haplotypes.
Were the atypical chromosomes as a group completely homogeneous to eventually justify its association with an increased risk of CVD? It seems that they are heterogeneous in sickle cell patients from Brazil6.
Have the authors analyzed the association between hematological features and CVD? Logistic regression showed that reticulocyte count was the main factor for CVD in our experience5.
It is likely that the discrepancies between the two study results are due to differences in methodological design, CVD definition and relative prevalence of α-thal and βS-haplotypes. Anyway, we congratulate the authors for the published data and we are sure that they contribute to foster debate and increase knowledge about this important topic.
1. Adams RJ, McKie VC, Carl EM, et al. Long-term stroke risk in children with sickle cell disease screened with transcranial Doppler. Ann Neurol 1997;42:699-704. [ Links ]
2. Filho IL, Leite AC, Moura PG, et al. Genetic polymorphisms and cerebrovascular disease in children with sickle cell anemia from Rio de Janeiro, Brazil. Arq Neuropsiquiatr 2011;69:431-435. [ Links ]
3. Belisário AR, Martins ML, Brito AM, Rodrigues CV, Silva CM, Viana MB. β-globin gene cluster haplotypes in a cohort of 221 children with sickle cell anemia or Sβº-thalassemia and their association with clinical and hematological features. Acta Haematol 2010;124:162-170. [ Links ]
4. Belisário AR, Rodrigues CV, Martins ML, Silva CM, Viana MB. Coinheritance of α-thalassemia decreases the risk of cerebrovascular disease in a cohort of children with sickle cell anemia. Hemoglobin 2010;34:516-529.
5. Silva CM, Giovani P, Viana MB. High reticulocyte count is an independent risk factor for cerebrovascular disease in children with sickle cell anemia. Pediatr Blood Cancer 2011;56:116-121. [ Links ]
6. Zago MA, Silva WA, Dalle B, et al. Atypical beta(s) haplotypes are generated by diverse genetic mechanisms. Am J Hematol 2000;63:79-84. [ Links ]
Marcos Borato Viana
Department of Pediatrics, Medical School of the Federal University of Minas Gerais
Avenida Alfredo Balena 190/267
30130-100 Belo Horizonte MG - Brasil
Received 30 January 2012
Received in final form 22 March 2012
Accepted 29 March 2012
Conflict of interest: There is no conflict of interest to declare.