Background: ABO blood group system plays a vital role in transfusion medicine, genetics understanding, inheritance pattern, and disease susceptibility; therefore, it is fundamental to have information on the distribution of these blood groups among any population. There is very slim published data about distribution of ABO blood groups in Sudan and lesser about subgroups.

Methods: Blood samples were collected from 100 students in faculty of Medicine, Al imam Al Mahdi university, Kosti, White Nile state, Sudan. Students were known to have either A or AB blood groups and were typed for A1 and A2 subgroups as well as RhD antigen.

Results: Among the A group there are 93.42% A1 subgroup and 6.6% A2 subgroup. Among the AB group there were 91.6% A1B and A2B was 8.33%.

Conclusion: Frequency of A2 subgroup among A and AB blood phenotypes are equal in Sudanese.

Keywords: blood, group, subgroup A₁, subgroup A₂, sudanese

Antigens of the ABO blood group system (i.e., A, B, and H antigens) and Rhesus factor were discovered more than one century ago by karl et al.^1,2 who is considering the father of transfusion medicine, and with this discovery he enabling physicians to transfuse blood without endangering the patient′s life. The ABO antigens are defined by carbohydrate moieties on the extracellular surface of the red blood cell (RBC) membranes,³ but they are also highly expressed on the surface of a variety of human cells and tissues, including epithelium, sensory neurons, platelets, and vascular endothelium.⁴ The ABO and Rh blood group system remain the most important blood group systems and the classical immuno genetic markers.^5,6 Blood group antigens play a vital role in transfusion medicine, genetics understanding, inheritance pattern, and disease susceptibility.⁷ ABO and Rh D system also have a key role in evolutionary biology, anthropology, studying migration patterns, forensic pathology, and medico-legal issues such as unmatched pregnancy and disputed paternity.⁸ The frequency of ABO blood groups varies greatly in different races and populations. In most populations, about 50% are Group O, followed closely by group A, with groups B and AB showing a much lower incidence.³ In Chinese population group B has higher frequencies⁹ and it is the commonest group in the Bengalese population.¹⁰

ABO subgroups are distinguished by decreased amounts of antigens on RBCs and, in secretors, present in the saliva.³ Variation in A antigen expression was recognized early in the twentieth century¹¹ and the A blood group was divided into A₁ and A₂^12,13 which are the two principal A subgroups. Subgroups weaker than A₂ are not frequent, and are characterized by a decreasing number of A antigen sites on the RBCs and a reciprocal increase in H antigen activity. Other subgroups of A include A_int, A₃, A_x, A_end, A_m and A_el are met only rarely in transfusion practice, and the last four cannot reliably b identified on the basis of blood typing tests alone.³ The frequency of the common A subgroups varies greatly among different populations. Approximately 80% of blood type A or AB are classified as A₁ or A₁B, the remaining 20% are either A₂ or A₂ B.^14,15 In study from India the frequency of A₁ and A₂ subgroups among A blood group was respectively 98.14% and 1.07%, in the AB group the frequency of A₁B was 89.28% and that of A₂B was 8.99%, this report described the proportion of A₂B among AB samples as significantly higher than that of A₂ in group A samples¹⁶ and approximately the same distribution is obtained by Bangera.¹⁷ In general frequencies of A₁and A₂ phenotypes are compatible with the Hardy-Weinberg equilibrium for the Mendelian inheritance of the allelic A₁ and A₂ genes, but in some populations, such as blacks and the Japanese, the frequency of the A₂B phenotype is significantly higher than the expected frequency based on the frequency of the A₂ phenotype.^18,19

A₂ and A₂B individuals may have anti-A₁ in their serum, which appears as an atypical cold agglutinin.¹⁶ Approximately 0.4% of A2 and 25% of A₂B individuals have anti-A₁ in the serum,²⁰ these antibodies become clinically significant when react at 37 °C and cause extensive destruction of A₁ cells.^21,22 These antibodies can interfere in routine blood grouping and can give incorrect blood typing or can rarely cause haemolytic transfusion reactions.¹⁷

In Sudan there is very slim published data about distribution of ABO blood groups,^23,24 frequency of the Rh antigens²⁵ and only one report²⁶ described the general frequency of A₁and A₂ among the blood donors and to the best of our knowledge there is no published work in the literature regarding distribution of subgroups(A₁,A₂) among individuals of group A neither distribution of subgroups (A₁B,A₂B) among individuals with group AB in Sudan. So in this study we aim to determine the frequency of subgroups(A₁,A₂), (A₁B,A₂B) Among individuals of group A and AB respectively in the students of Faculty of Medicine and Health Sciences at AL imam Al Mahdi university, Kosti, White Nile ,Sudan.

100 students known having blood group A or AB were recurred for this study after an oral informed consent had been obtained. Standard method for ABO blood group was used to confirm the blood group and Rh status. Samples were further tested with anti-A₁ lectin to classify them into A₁, A₂. Whenever the agglutination was 4+ with anti-A antisera but negative with anti-A₁ lectin, the sample was considered as A₂ subgroup. The significance of differences in proportions was analyzed using percent test.

Distribution of A and AB blood groups in the total population of the study is shown in Table 1. 97% of the total sample was positive for Rh D antigen. Distribution of A subgroups and AB subgroups among A and AB respectively are shown in Figure 1 & 2. Frequency of A₂B subgroup among AB group was slightly higher than frequency of A₂ among A group (Table 2) but was statistically insignificant (percent test). Ratio of A₂/A₁ is0.07 and that of A₂B/A₁B is 0.09.

Figure 1 Distribution of ¹ and ² subgroup among A group (%).

Figure 2 Distribution of ¹B and ²B subgroup among AB group (%).

The frequency of the common ABO phenotypes (A₁, A₂, B, A₁B, A₂B and O) varies greatly among different populations.^14,27 Populations with a high frequency of A phenotype are found mainly in Northern and Central Europe. The B phenotype is most frequent in Central Asia and almost absent in Amerindians. Blood group O is the most frequent phenotype in a global perspective.⁴ In this study 100 blood samples we collected from students of faculty of Medicine, Al imam Al Mahdi University, they were known to have either A or AB blood group and this was confirmed in each sample. Among this studied sample there were 76% group A and 24% group AB (Table 1) and this is in consisting with the previous studies done in Sudanese^25,26 which also showed a higher frequencies of A group than AB group.97% of our population were positive for RhD antigen which matches previously reported per cents in Sudanese.^25,26 Our results showed that A₁ is the commonest sub group among A group (Figure 1) and A₁B is the commonest subgroup among AB group (Figure 2) which is in agreement with^16,18,28 which reported the same distributions in Indian, Japanese and South Africans respectively. Which means that A₂ and A₂B are rare subgroups. But still they are important because anti-A₁ antibodies occur in sera of A₂ groups and more common in A₂B subgroups²⁰ and can be encountered during clinical practice,²⁹ causing difficulties in blood typing,³⁰ hemolytic transfusion reaction²² and complicate organs transplantation.³¹ In this study the frequency of A₂B subgroup in AB group is slightly higher than that of A₂ subgroup in A group (Table 2), but this difference is statistically insignificant, so the frequencies of A₂ and A₂B among A and AB groups respectively are in balance, which is in agreement with studies done in Caucasian population,^14,32 but in contrast to studies done in blacks population.^14,28 Indian,¹⁶ Japanese¹⁸ and Chinese³³ because studies performed among all those populations reported imbalance in the frequencies of A₂ and A₂B in A and AB positive individuals, respectively. This imbalance in blacks has been explained by domination of the B gene on phenol typing expression of A₁B causing this A₁ to be expressed as A₂ or A_int leading to A₂B excess.^28,34,35 In Japanese the higher frequency of A₂ in AB group was explained by the different expressions of the allele R101, which is expressed as phenotype A₁ in *R101/*O heterozygous individuals, but as phenotype A₂ in *R101/*B hetero zygotes, thus giving rise to a higher A₂B phenotype frequency.¹⁹ This super active B gene has been reported as a control for expression of the super active B* enzyme, exists in both blacks and Japanese.¹⁸

In conclusion frequency of A₂ subgroup among A and AB blood phenotypes are almost equal in Sudanese, which is a surprise, because Sudanese ethnic groups are mainly African and the balanced distribution is a character of Caucasian groups. This can be related to the fact that Sudanese are a mixture of different ethnic groups.³⁶

None.

The author declares no conflict of interest.

1. Landsteiner K. ZurKenntnis der antifermentativen, 7. lytischen und agglutinierendenWirkungen des Blutserums und der Lymphe. ZblBakt. 1990;27:357–362.
2. Landsteiner K. Über Agglutination serscheinungen nor8. Malen Menschlichen Blutes. Wien KlinWochenschr. 1901;14:1132–1134.
3. Franchini M, Liumbruno GM. ABO blood group: old dogma, new perspectives. ClinChem Lab Med. 2013;51(8):1545–1553.
4. Storry JR, Olsson ML. The ABO blood group system revisited: a review and update. Immunohematology. 2009;25(2):48–59.
5. RW. Introduction to blood transfusion technology. ISBT Science Series. 2008;3(2):xiii–xiv.
6. Ilyas M, Iftikhar M, Ullah R. Frequency of ABO and Rh blood groups in Gujranwala (Punjab), Pakistan. Biologia. 2013;59(1):107–114.
7. Khan MS, Subhan F, Tahir F, et al. Prevalence of blood groups and Rh factor in Bannu region (Pakistan). Pak J Med Res. 2004;43(1):8–10.
8. Piyush P, Sangeetha PP. Frequency and distribution of blood groups in blood bank donors. National journal of medical Research. 2012;2(2):202–206.
9.  Napier JAF. Handbook of blood transfusion therapy. 2nd ed. USA: John Wiley & Sons Ltd; 1996.
10. Mollison PL, Engelfriet CP, Contreras MK. Blood transfusion in clinical medicine. 9th ed. Blackwell Scientific Publications; 1993. 150 p.
11. Race RR, Sanger R. Blood groups in man. 6th ed. United Kingdom: Blackwell Scientific Publications; 1975.
12. VonDungern E, Hirzsfeld L. Uber die gruppens11. pezifischestrukturen des blutes III. ImmunForsch. 21918:526–562.
13. Camp FR, Ellis FR. Selected contributions to the literature of blood groups and immunology. Fort Knox, USA: US Army Medical Research Laboratory; 1966.
14. Mourant AE, Kope AC, Domaniewska K. The distribution of human blood groups and other polymorphisms. 2nd ed. New York, USA: Oxford University Press; 1977.
15. Roychoudhuri AK, Nei M. Human polymorphic genes world distribution. Oxford: New York, USA: Oxford University Press; 1988.
16. Shamee Shastry, Sudha Bhat. Imbalance in A2 and A2B phenotype frequency of ABO group in South India. Blood Transfus. 2010;8(4):267–270.
17. Bangera IS, Fernandes H, Swethadri GK, et al. Prevalence of A2 sub group in A and AB blood groups and the transfusion implications. Asian Journal of Transfusion Science. 2007;1(2):103.
18. Yoshida A, Dave V, Hamilton HB. Imbalance of blood group A subtypes and the existence of super active B gene in Japanese in Hiroshima and Nagasaki. Am J Hum Genet. 1988;43(4):422–428.
19.  Ogasawara K, Yabe R, Uchikawa M, et al. Different alleles cause an imbalance in A2 and A2B phenotypes of the ABO blood group. Vox Sang. 1998;74(4):242–247.
20. Rudmann SV. Textbook of Blood Banking and Transfusion Medicine. 1st ed. WB Saunders, USA; 1995. p. 73–75.
21. Boorman KE, Dodd BE, Loutit JF. Some results of transfusion of blood to recipients with “cold agglutinin”. Br Med J. 1946;1:751–754.
22. Chaudhary R, SonkarA. High titer immunizing anti-A1 in an A2B patient resulting in hemolytic transfusion reaction. Transfusion Bulletin. 2004;12(2):2004–2008.
23. Abo Algasim EI, Malik H, et al. Frequencies of ABO, Rh-D and Kell (Kpa, Kpb) Blood Group Antigens in Dinka Sudanese ethnic group. SUST 01-12; 2007.
24. Khalil IA, Phrykian S, Farr AD. Blood group distribution in Sudan. Gene Geogr. 1989;3(1):7–10.
25. Shahata WM, Khalil HB, Awad-Elkareem A, et al. Blood group and Rhesus antigens among blood donors attending the central blood bank, Sudan. Sudan JMS. 2012;7(4):245–248.
26. Hassan FM. Frequency of ABO, Subgroup ABO and Rh(D)blood groups in major sudanese ethnic Groups. Pak J Med Res. 2010;49(1):21–23.
27. Roychoudhuri AK, Nei M. Human polymorphic genes 13. World distribution. USA: Oxford University Press; 1988.
28. May RM, Du Toit ED. Blood group gene frequencies of four population groups in the western cape. S Afr Med J. 1989;76(12):647–650.
29. Chaudhari Surg Cdr CN, Surg Capt RN Misra, Col AK Nagpal. Transfusion in blood group A2B with anti A1 recipient. MJAFI. 2008;64:371–372.
30. Padmasri R, Urvashi Bhatara, Iyengar RS. A Rare Case of A2+ve Blood group in an obstetric emergency. J Clin Diagn Res. 2014;8(2):181–182.
31. Brecher ME, Moore SB, Reisner RK, et al. Delayed hemolysis resulting from anti-A1 after liver transplantation. Am J Clin Pathol. 1989;91(2):232–258.
32. Voak D, Lodge TW, Stapleton RR, et al. The incidence of H deficient A2 and A2B bloods and family studies on the AH-ABH status of an Aint and some new variant blood types (Aint H-A1, A2-HWA1, A2BHWA1B and A2-BHWA2B). Vox Sang. 1970;19(1):73–84.
33. Ying Y, Hong X, Xu X, et al. Serological characteristic and molecular basis of A2 subgroup in the Chinese population. Transfus Apher Sci. 2013;48(1):67–74.
34. Ssebabi ECT. Action of African B gene on A, sub group A. Vox Sang. 1976;30(2):208–210.
35. Voak D, TW Lodge, JV Reed. A possible explanation for the expression of A2B phenotypes observed in some populations. Vox Sang. 1970;18:471–474.
36. Royal Anthropological Institute of Great Britain and Ireland, JSTOR (Organization). Journal of the royal anthropological institute of great Britain and Ireland; 1999. 17 p.