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GENETIC VARIATION OF BLOOD GROUPS BETWEEN KHAYANGS AND OTHER ETHNIC COMMUNITIES OF BANGLADESH Gourab Dewan1* Preeti Prasun Barua2 Narayan Chandra Das3 Sanjib Kumar Purohit4 Rownak Jahan5 Abul Kalam Azad6 Abstract Background: Gene diversity of the Khayang community of Bangladesh is undetermined. Methods: A descriptive study was carried out among Khayang communities of Rajasthalithana, Rangamati district. We determined ABO and rhesus blood groups. Allele frequency of blood groups was determined using Hardy-Weinberg formula. Obtained allele frequency was compared with eight ethnic groups of Bangladesh. Results: 118 participants blood group was determined. ABO phenotypic frequency was A > O > AB > B. Allele frequency was IO 0.5821, IA 0.2863 and IB 0.1316 and (O > A > B). Khayang have highest frequency of group A and lowest frequency of group B among ethnic population of Bangladesh. Observed heterozygosity was 0.5618. Comparative study showed allele frequency of the Khayang community differed significantly from eight ethnic communities of Bangladesh (p < 0.0001). No rhesus negative blood group was found. Conclusion: Khayang community show significant genetic diversity. Their ABO phenotypic frequency and allelic distribution is different from other ethnic communities of Bangladesh. Therefore Khayangsare unique ethnic population group in their blood group antigen inheritance. Key words: Gene; Khayang; Bangladesh; Allele; Blood group.
Pangkhua, Khayang, Lushai, Mru and Khumi4. They have radiated to inhabit different geographical locations of Bangladesh. As yet, the nature of their genetic diversification has not been explored. It seems interesting to examine the genetic structure of representative Khayang populations. Hence, we have employed classical blood group markers (i.e ABO and Rh) to understand genetic difference of the Khayangs.
Introduction Genetic evaluation of ethnic population of Bangladesh is sparse. In resource constrained settings like ours feasible genetic markers for such evaluation are ABO and rhesus (Rh) blood group genes1. Few studies have examined genetic variation among Bangladeshi ethnic population2. As many as 25 ethnic communities resides in Bangladesh3. Khayangs are ethnic minorities living in Chittagong Hill Tracts (CHT). They belong to Kuki community. Kuki community of Bangladesh is known as Chin in Myanmar and Mizo in India. This group in Bangladesh consists of six ethnic groups- Bawm,
Materials and methods Khayang is one of the smallest ethnic groups in CHT. Their current population is approximately 45004. This was a descriptive study. The required sample size for allele frequency determination is 1005. We determined Blood group of 118 Khayang participants.Place of study was Kuki Para at Rajasthalithana of Rangamati district. All the participants gave written consent. Purposive sampling technique was followed during selection of participants. We employed serological tests to determine phenotype of ABO and rhesus (D) systems. We used Anti-A, anti-B and anti-D (Blended IgM and IgG) antibody of Atlas Medical®, William James House, Cowley Rd, Cambridge, UK. Corresponding antigen in red cell membrane of a subject (Forward blood grouping method) was detected by slide method. In ABO system there are four phenotypes (A, B, AB and O) and six genotypes (AA, AO, BB, BO, AB and OO). In rhesus system there are two phenotypes (Rhesus positive/negative) and three genotypes (DD, Dd and dd). Phenotypic frequencies were expressed
1. Assistant Professor of Medicine Rangamati Medical College, Rangamati. 2. Associate Professor of Community Medicine Rangamati Medical College, Rangamati. 3. Medical Officer of Community Medicine Chittagong Medical College, Chittagong. 4. Associate Professor of Medicine Rangamati Medical College, Rangamati. 5. Associate Professor of Gynaecology and Obstetrics Rangamati Medical College, Rangamati. 6. Associate Professor of Paediatrics Rangamati Medical College, Rangamati. Correspondence: Dr. GourabDewan Cell: 01712599770 E-mail:
[email protected] Received on Accepted on
: 22.11.2017 : 26.11.2017
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Volume 21 Number 2 July 2017
as percentages. From the observed phenotypic frequencies, allele frequency for ABO (IA, IB and IO) and rhesus (D) system (ID and Id) were calculated by Hardy-Weinberg formula as mentioned by Agrawal et al6. This is a standard formula of quantitative population genetics. Results were expressed according to convention in decimal where all allele frequencies add up to 1.00. Genotypic frequency of ABO and rhesus systems was expressed in decimal. With Chi-square test we compared observed phenotypic frequencies of ABO system. Statistical difference considered significant when p < 0.05 at 95% confidence interval.
Table III : Interethnic comparison of allele frequency of ABO system Ethnic group Location
Allele frequency IB IO Khayang CHT 0.2863 0.1316 0.5821 Chakma CHT 0.2246 0.2897 0.4857 Marma CHT 0.1672 0.3394 0.4934 Tripura CHT 0.3646 0.2896 0.3458 Tanchangya CHT 0.2303 0.2794 0.4903 Garo Mymensingh 0.2921 0.2226 0.4853 Khasia Sylhet 0.2042 0.2018 0.5940 Manipuri Moulvibazar 0.2724 0.1061 0.6215 Santal Rajshahi 0.1985 0.2895 0.5120 IA
Results We obtained blood sample from 118 participants. ABO blood group frequency was A 41.52% (n = 49) O 33.89% (n = 40) AB 13.56% (n = 16) and B 11.01% (n = 13). Observed phenotypic frequency was A > O > AB >B. There was no rhesus negative blood group. Allelic and genotypic frequencies obtained from observed phenotypic frequency is presented in table I. Interethnic comparison of phenotypic and allelic frequencies of the Khayang presented in table II and III respectively. Khayang have significant difference in allele distribution of ABO system (p < 0.0001) when compared with eight separate ethnic groups.
Characteristics Frequency Allele type IA 0.2863 IB 0.1316 IO 0.5821 Genotype AA 0.0821 AO 0.3333 BB 0.0173 BO 0.1532 OO 0.3389 AB 0.0753 Table II : Comparison of ABO and rhesus (D) blood groups of ethnic groups of Bangladesh Rhesus (D) +Ve -Ve 100.0 99.5 0.5 99.4 0.6 100.0 97.5 2.5 99.1 0.9 100.0 97.1 2.9 100.0 -
Ref
< 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001 < 0.0001
2 2 2 2 7 8 8 9
Discussion Significant variation in allele frequency indicates genetic variation. As an ethnic group the Khayangs show significant difference in frequency of ABO allele. Among tribal population of CHT Khayangs have the highest frequency of “O” allele. However, even higher frequency of IO was reported among Khasia and Manipuris from Sylhet8. While IA frequency of the Khayangs is within the range of previously observed values among ethnic communities of Rangamati, those of IB is lower2. Only IA frequency closely matched with the Garo and the Manipuri but not IO or IB(Table III).
Table I: Allele and genotypic frequency of ABO blood group system
Ethnic ABO system group A B O AB Khayang 41.5 11.0 33.9 13.5 Chakma 27.9 36.8 23.3 12.6 Marma 19.7 45.3 24.0 10.9 Tripura 38.5 28.4 11.9 21.1 Tanchangya 28.4 35.8 23.6 12.2 Garo 36.9 31.1 23.6 8.4 Khasia 28.4 28.4 35.2 7.8 Manipuri 41.2 12.9 38.6 7.1 Santal 24.27 38.83 26.22 10.68
χ2
Allele frequency of the Khayang correlates with the Garo, Khasia and Manipuri population (O > A > B). It differs for the Chakma, Marma, Tanchangya, Santal (O > B > A) and Tripura (A > O > B)2,7-9. Phenotypic frequency of the Khayangs (A > O > AB > B) is different from all the compared communities. They also have the highest frequency of group A (41.5%) and the lowest frequency of group B (10.0%) among the ethnic groups of Bangladesh. Generally AB is the least common group in ABO system worldwide. All the nine communities except Khayangs (B) and Tripura (O) had AB as the least frequent group. If compared with the Bengali communities; Bengali people from eastern Bangladesh shows O > B > A > AB and those from western Bangladesh shows B > O > A > AB pattern2.
Phenotypic Ref frequency A > O > AB > B B > A > O > AB 2 B > O > A > AB 2 A > B > AB > O 2 B > A > O > AB 2 A > B > O > AB 7 O > A = B > AB 8 A > O > B > AB 8 B > O > A > AB 9
Khayang, Tripura, Garo and Manipuris are so far the only known communities in whom group A is predominant in Bangladesh2,7,8. However, frequency of group A in the later three ethnic groups was lower (range 36.9 to 41.2%) than the Khayangs (41.5%)2,7,8. This high frequency of group A may be due to practice of consanguinity or small population size. 2
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Blood group B is generally predominant among Asian population of Mongoloid origin. Group B is dominant among Chakma, Marma and Tanchangya2. Among Tripura and Garo it is second in frequency; Manipuris have “B” as third in frequency2,7,8. But Khayang have B as the least common group. All seven ethnic groups mentioned here have Mongoloid background.Khasiaare of Austric origin and have “O” predominance whereasSantals are Australoid in origin and “B” is predominant among them3.
References 1. Farhud DD, YeganehMZ .A Brief History of Human Blood Groups.Iranian J Publ Health. 2013; 42(1):1-6. 2. Dewan G. Comparative frequency and allelic of ABO and Rh (D) blood groups of major tribal communities of southern Bangladesh with general population and their determinants. Egypt J Med Hum Genet. 2015; 16 (2):141-147
Important determinant of blood group antigen frequency is environmental selection pressure. As group O is protective against malaria it occurs in high frequency among Africans2. Protective role of ABO blood group against malaria is not clear in Indian subcontinent2. Despite living in a malaria endemic zone, none of the communities from CHT have high frequency of group O2. Dewan previously hypothesized that like other south-east Asian countries, high frequency of hemoglobin E mutation among ethnic communities of CHT plays a major role in malaria protection rather than blood group O2. Hemoglobin E homozygous or heterozygous state was observed in ~ 49% Khayangs of CHT10. This observation supports his hypothesis.
3. Sarkar J, Ghosh G, editor. Populations of the SAARC countries: Bio-cultural perspectives. New Delhi: Sterling Publishers Pvt. Ltd. 2003. 4. Kim A, Roy P, Sangma M. The Kuki-Chin Communities of Bangladesh: A sociolinguistic survey. SIL International. [Cited 2016, Nov 25] Available from: www.01.sil.org/silesr/2011/silesr2011-025.pdf 5. Chakraborty R. Sample size requirements for addressing the population genetic issues of forensic use of DNA typing. Hum Biol. 1992; 64(2):141-159. 6. Agrawal A, Tiwari AK, Mehta N, Bhattacharya P, Wankhede R, Tulsiani S et.al. ABO and Rh (D) group distribution and gene frequency, the first multicentric study in India. Asian J Transfus Sci. 2014; 8:121-125.
Frequency of Rh-Ve blood group was low in all ethnic communities of Bangladesh in previous observations2,7-9. Similar to the Tripura, Khasia and Santals we observed no Rh-Ve blood group among Khayangs.
7. Sultana R, Rahman Z, Sunyal DK, Masud MAA, Molla GM, Begum R, et al. Comparison of ABO and Rh-D blood group systems between the Garo tribal people of Mymensingh and general people of Dhaka city. J Enam Med Col 2011;1(1):31–35.
The observed variations may reflect the diverse ancestry, subsequent evolution of the Khayang community. Small population size, migration, scattered places of living and subsequent endogamous mating and possible founder effect may have influenced pattern of blood group antigen inheritance of the Khayangs.
8. Begum D, Amin MR, Khatun F, Ahmed SS, Sinha SK, Rahman MA. Distribution of ABO and Rh blood groups among tribal population of Sylhet, Bangladesh. J Dhaka Med Coll. 2011; 20(1):44–50. 9. Haque KMG, Rahman M, Hussain M. Clinically important blood group antigens in six different tribal populations of Bangladesh. Transfus Today. 1999; 39:6 –7.
Conclusion Khayang people have significantly different allele distribution in ABO blood group system. They have the highest frequency of group A and lowest frequency of group B among ethnic population of Bangladesh. Observed results fill the information gap on genetic diversity of Khayang ethnic community from Bangladesh.
10. Shannon KL, Ahmed S, Rahman H, Prue CS, Khyang J , Ram M et al. Hemoglobin E and Glucose6-Phosphate Dehydrogenase Deficiency and Plasmodium falciparum Malaria in the Chittagong Hill Districts of Bangladesh..Am J Trop Med Hyg.2015 ;93(2):281-286.
Disclosure All the authors declared no competing interest.
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