Blood group polymorphisms in Brazil^☆

Blood group antigens are polymorphisms of proteins and carbohydrates on the surface of red blood cells (RBC) with the distribution of alleles varying between different ethnic groups and populations. By using the genetic information provided by the human genome project, the molecular basis of most blood group genes encoding blood group systems, antigens and phenotypes have been elucidated and nowadays the molecular basis is known for the 308 antigens clustered in the 36 blood group systems recognized by the International Society of Blood Transfusion (ISBT).¹ This knowledge has provided the means to predict red cell antigens and phenotypes in order to identify more extensively matched blood for chronically transfused patients. However, data on the prevalence of various blood group antigens in different populations are essential for estimating the availability of blood components.

The available wealth of serologically defined variants has contributed to the rapid rate with which the genetic diversity of blood group genes has been revealed. Initially, molecular information associated to each variant was obtained from only a small number of samples and applied to DNA analysis with the hopeful assumption that the molecular analysis would correlate with RBC antigen typing. By gathering more information, it became obvious that many molecular events result in the genotype and RBC phenotype being apparently discrepant.² Therefore, a large number of people from a variety of ethnic backgrounds need to be studied to determine the occurrence of particular genotypes and to establish more reliably the correlation between blood group genotype and phenotype.

Hemagglutination has identified many phenotypic variants and molecular analysis has revealed remarkable variations within variants. Investigations on the automation of SNP and DNA sequence analysis are ongoing and the potential for genotyping large numbers of samples has already been achieved.³ Several assays for blood group genotyping have been developed to predict the blood group antigen profile of an individual and with the development of several commercial kits, molecular testing is being performed in many laboratories worldwide to solve clinical problems that cannot be addressed by hemagglutination.

The identification of the molecular basis of blood group antigens has also provided an insight into the generation of gene diversity in humans showing that blood group polymorphisms can be useful markers of genetic differentiation of human populations. The effects of mutations on protein expression and the relative ease of identifying individuals bearing variant alleles has led to the proposal that genes encoding blood group antigens are an important and unique resource for studies on human DNA variation.⁴

The Brazilian population is of heterogeneous ethnic origin. This diverse population is also unevenly distributed within a country of continental dimensions. Besides the Native-American population, Brazil received many immigrants from Portugal, Italy, Spain, Germany, Japan and the Middle East. During the slave trade from the 16th to the 18th century Brazil received approximately 4 million Africans, mainly from Angola, Congo and Mozambique, who settled in almost all regions of the country.⁵ The intense process of miscegenation made the Brazilian population unique in its ethnic background. In a multi-ethnic population, such as that of Brazil, the frequencies of the different blood group antigens vary significantly. Genotyping studies in this population have shown that the blood group polymorphisms differ significantly from other populations^6and7 and studies inside the country have also shown a heterogeneous distribution of blood group alleles and variants between groups of people from different regions.^8and9 Moreover, the high degree of genetic mixture in the Brazilian population facilitates the generation of new alleles.^10and11 Therefore, studies on the distribution of blood group alleles and variants in donors and patients from different regions of Brazil can report the frequencies of defined polymorphic blood group antigens that function as receptors for parasites, map the rare phenotypes across the country and contribute in the selection of the most adequate blood component for chronically transfused patients.

References

• ¹
  SBT- Blood Group Allele Terminology [monograph on the internet]. Available from: http://www.isbtweb.org/working-parties/red-cell-immunogenetics-and-blood-group-terminology/blood-group-terminology/blood-group-allele-terminology/
  » http://www.isbtweb.org/working-parties/red-cell-immunogenetics-and-blood-group-terminology/blood-group-terminology/blood-group-allele-terminology/
• ²
  Reid ME. Applications of DNA-based assays in blood group antigen and antibody identification. Transfusion. 2003;43(12):1748-57.
• ³
  Flegel WA, Gottschall JL, Denomme GA. Integration of red cell genotyping into the blood supply chain: a population-based study. Lancet Haematol. 2015;2(7):e282-9.
• ⁴
  Blumenfeld OO, Patnaik SK. Allelic genes of blood group antigens: a source of humans mutations and cSNPs documented in the Blood Group Antigen Gene Mutation Database. Hum Mutat. 2004;23(1):8-16.
• ⁵
  Curtin PD. Atlantic slave trade: a census. Milwaukee: University of Wisconsin Press; 1969.
• ⁶
  Pellegrino J Jr, Castilho L, Rios M, De Souza CA. Blood group genotyping in a population of highly diverse ancestry. J Clin Lab Anal. 2001;15(1):8-13.
• ⁷
  Castilho L, Baleotti W Jr, Tossas E, Hue- Roye K, Ribeiro KR, Lomas- Francis C, et al. Molecular studies of DO alleles reveal that JO is more prevalent than HY in Brazil, whereas HY is more prevalent in New York. Immunohematology. 2008;24(4):135-7.
• ⁸
  Piassi FC, Santos SM, de Castilho LM, Baleotti Júnior W, Suzuki RB, da Cunha DM. Dombrock genotyping in Brazilian blood donors reveals different regional frequencies of the HY allele. Rev Bras Hematol Hemoter. 2013;35(6):400-3.
• ⁹
  Flôres MA, Visentainer JE, Guelsin GA, Fracasso Ade S, de Melo FC, Hashimoto MN, et al. Rh, Kell, Duffy, Kidd and Diego blood group system polymorphism in Brazilian Japanese descendants. Transfus Apher Sci. 2014;50(1):123-8.
• ¹⁰
  Baleotti W Jr, Rios M, Reid ME, Hashmi G, Fabron A Jr, Pellegrino J Jr, et al. Dombrock gene analysis in Brazilian people reveals novel alleles. Vox Sang. 2006;91(1):81-7.
• ¹¹
  Arnoni CP, Muniz JG, Gazito D, Person Rde M, Vendrame TA, Castilho L, et al. Novel RHAG allele encoding the Rh(null) phenotype in Brazil. Transfusion. 2015;55(10):2521-2.

• ☆
  See paper by Costa et al. on pages 199-205.

Publication Dates

• Publication in this collection
  Jul-Sep 2016