Genotypes and allele frequencies of ACE insertion/deletion polymorphism among Omanis 25 Genotypes and allele frequencies of angiotensin converting enzyme (ACE) insertion/deletion polymorphism among Omanis. *Ali T. Al-Hinai1, Mohammed O Hassan2, Mehmet Simsek3, Hameeda Al-Barwani3, Riad Bayoumi3 ABSTRAC T. Objective: To describe the angiotensin converting enzyme (ACE) genotype frequencies among Omani Arabs. Method: A polymerase chain reaction (PCR) test, based on separation of different size DNA fragments, was developed to test the presence or absence (polymorphism) of a small DNA deletion in the ACE gene. The subjects were 124 Omani Arab students of Sultan Qaboos University, Muscat. Results: The frequency of the I allele was 0.29, while that of the D allele was 0.71. The gene frequency distribution did not deviate from Hardy-Weinberg equilibrium. Conclusions: The frequency of D allele among Omanis is similar to that among other Arabs and Africans, but differs significantly from that among the Japanese and Chinese. Key Words: Allele, genotype, polymorphism, hypertension. Departments of 1Medicine, 2Physiology and 3Biochemistry, College of Medicine & H Sc, Sultan Qaboos University, P.O.Box 35, Al-Khod-123, Sultanate of Oman. *To whom correspondence should be addressed. Email: alihinai@squ.edu.om ESSENTIAL HYPERTENSION (HTN) IS A MAJOR RISK factor for morbidity and mortality from car-diovascular diseases.1 The causes of HTN have not yet been determined. It is considered as a multifacto- rial and polygenic disease,2 and occurs as a consequence of a complex interplay of genetic alterations and envi- ronmental factors.3 The angiotensin converting enzyme (ACE) gene is one of the genes that control blood pres- sure and has been intensively investigated. The ACE gene, first described by Rigat et al in 990,4 has an inser- tion/deletion (I/D) polymorphism in intron 6. Various published reports suggest an association or linkage of the D allele of the ACE gene with myocardial infarction,5 essential hypertension,6 left ventricular hypertrophy,7 renal insufficiency8 and high fasting blood sugar levels.9 However, some other investigators have found no asso- ciation between ACE I/D polymorphism and HTN.10,11 Inter-ethnic variations in the frequency of allelic forms of certain genes, have been suggested as one of the rea- sons for such discrepancies.12 This is particularly true for the ACE gene, since wide inter-ethnic allelic variations have been reported.13 The aim of our study was to find out ACE allele and genotype frequencies among Omani Arabs and compare them with those among other ethnic groups. Oman is one of the countries in Arabian Peninsula, and 85% of its population are Arabs of Bedouin descent; the remaining 5% originate from Eastern Africa and the Indian sub- continent.14 S U B J E C T S One hundred and twenty four (24) unrelated Omani Arabs were randomly selected from among students of Sultan Qaboos University. After getting an informed consent, 5 ml of blood was collected from each into an EDTA-containing tube. SQU JOURNAL FOR SCIENTIFIC RESEARCH: MEDICAL SCIENCES 2002, VOL. 4, NO. –2, 25–27 ©SULTAN QABOOS UNIVERSIT Y Dr Al hinai ����� ������� ������ ����������� ) ����� (����������� ������ ������ ��������� ��������� �� �������� ������� � ����� ������ ��� ����� ����� ������� ���� �������� ����� �������� ����� �������� :����� :���� ������� �������� ��������� �� ����������� ���� ����� ������� ����� ���� �����.������� :�� ��� ���� ��� ��� �� ���� � ������ ������ ��� ����� ��� ������� �������� ������� ���� ����� ������ �� ���� ����� ������� ���������� ������ ������ ������ �� ������� ���� �� ������ ������ �� ���� �� .��� ������������ ����� ��� �� ����� ���� �� ��������� ������.�������:���� ���� ���)���� (I���������� ���� ��� ����� �D������ . �� ������ ���� ������ �� ������ � ����� ����� �� ����������:���� ���� ��D�� ������ ����� ���� �������� ������ ����� �� ������ ������ ��� ��������� �� ��� �� �������������� ������� . 26 DNA ANALYSIS DNA was isolated from leukocytes by phenol/chlo- roform extraction. The insertion/deletion (I/D) poly- morphism in intron 6 of the ACE gene was detected by the polymerase chain reaction (PCR), following the method described previously by Rigat et al,15 using a set of oligonucleotide primers which differentiate the three ACE genotypes: II, ID and DD. Using 2% agarose gel electrophoresis and ethidium bromide staining, the homozygote deletion (DD) alleles were visualised as 90 base pairs (bp) bands, homozygote insertion (II) alleles as 490bp bands, and heterozygotes (ID) alleles as two bands of 490 bp and 90 bp. Since the D alleles in hetero- zygous samples (ID) are prefer- entially amplified, some samples with ID genotypes are liable to be mistyped as DD.16 Therefore, each sample found to have the DD gen- otype was verified in an independ- ent second PCR amplification. A 335 bp band was visualised only in the presence of an I allele and no bands were visualized in samples with DD. R E S U L T S The frequency distribution of gen- otypes and alleles of the ACE (I/ D) polymorphism among Omani Arabs is summarised in Table . The frequency of the I allele was 0.29 while that of the D allele was 0.7. Ten heterozygotes were mistyped as DD, but proved to be heterozy- gotes on independent second PCR using insertion specific primers. The gene frequency distribution did not deviate from the Hardy-Weinberg equilibrium. D I S C U S S I O N The frequency of the D allele of the ACE gene among Omanis (0.7) is comparable to that in other Arabs, such as the Emiratis (0.66), Somalis (0.73) and Sudanese (0.64). Compared to other ethnic groups (Table 2) the frequency of the D allele seems to be among the highest reported. The frequency of the D allele seems to follow a clinal distribution, being highest among Africans and Arabs (0.70–0.60), followed by Caucasians (0.46–0.58), then the Japanese (0.33–0.35) and the Chinese (0.29). The Yanomami Indians and Samoans seem to have the lowest frequencies: 0.5 and 0.09, respectively. C O N C L U S I O N This study confirms the results obtained among other Arabs and adds to the data indicating the wide variations observed in the frequency of the ACE alleles among the peoples of the world. Therefore, the interpretation of clinical data on the association of the ACE alleles with cardiovascular disease must be approached with the greatest of care. Table 2. Prevalence of insertion/deletion polymorphisms of ACE gene among different ethnic groups as per different studies. Allele Frequency Ethnic group I D Number of Individuals tested I. Arabs Emirates17, 18 Sudanese18 Somalis18 Omanis (present study) 0.34 0.39 0.36 0.27 0.29 0.66 0.61 0.64 0.73 0.71 159 111 121 53 124 II. Africans Nigerians13 African-Americans19 0.41 0.30 0.59 0.70 80 40 III. Caucasians5,20,21 0.42–0.54 0.46–0.58 1212 IV. Asians Japanese22,23,24 Chinese25 0.65–0.67 0.71 0.33–0.35 0.29 354 189 V. Others: Yanomami Indians13 Samoans13 0.85 0.91 0.15 0.09 49 58 Table 1. Frequency of genotypes and alleles of ACE (I/D) polymorphism in 124 Omani Arabs. Genotypes Allele fequency Total Number II (n) O(E) ID (n) O(E) DD (n) O(E) I D 124 8(10.1) 55(50.6) 61(63.2) 0.29 0.7 1 O: Observed, (E): Expected �2 : 0.896, for Goodness of Fit Test. No deviation from the Hardy-Weinberg equilibrium was observed. A L H I N A I E T A L 27 R E F E R E N C E S . MacMahon S, Peto R, Cutler J, Collins R, Sorlie P, Neaton J, et al. Blood pressure, stroke and coronary heart disease: part I, prolonged difference in blood pressure: prospective obser- vational studies corrected for the regression dilution bias. Lancet, 990, 335, 766–774. 2. Lifton RP, Jeunemaitre X. Finding genes that cause human hypertension. J Hypertens, 993, , 23–236. 3. Hamet P, Pausova Z, Adarichev V, Adaricheva K, Tremblay J. Hypertension: genes and environment. J Hyertens, 998, 6, 397–48. 4. 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