Gene frequencies of human platelet alloantigens in Bahraini Arabs.

Abstract

Human platelet antigens (HPA) are implicated in the pathophysiology of certain hematological disorders, and as varied distribution of HPA-1 alleles and genotypes were reported fordifferent countries and ethnic populations, we determined the distribution of HPA-1, -2, -3, -4, and -5 alleles, genotypes and haplotypes for 194 healthy Bahraini subjects by polymerase chain reaction with sequence specific primers. The distribution of the HPA polymorphisms was in Hardy-Weinberg equilibrium. Allele frequencies of 0.76 and 0.24 (HPA-1a and -1b), 0.77 and 0.23 (HPA-2a and -2b), 0.57 and 0.43 (HPA-3a and -3b), 0.93 and 0.07 (HPA-4a and -4b), and 0.86 and 0.13 (HPA-5a and -5b) were seen. With the exception of HPA-3a/a (30.4%), the frequencies of homozygous HPA-1a/a (56.8%), 2a/a (60.1%), 4a/a (87.2%), and 5a/a (75.7%) were higher than those of heterozygous (a/b) or homozygous (b/b) variants. Our results provide basic information for further studies of the HPA system polymorphism, which in turn will be instrumental in understanding and treating immune-mediated platelet disorders.

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Gene Frequencies of Human Platelet Alloantigens
in Bahraini Arabs
Abeer M. Al-Subaie,1Iman K. Al-Absi,1Khadija Al-Ola,2Sarra Saidi,3
Naglaa A. Fawaz,4and Wassim Y. Almawi1*
1Department of Medical Biochemistry, College of Medicine and Medical Sciences, Arabian Gulf University, Manama, Bahrain
2Department of Pediatrics, Salmaniya Medical Complex, Manama, Bahrain
3Faculty of Pharmacy, University of Monastir, Monastir, Tunisia
4Faculty of Medicine, King Faisal University, Dammam, Saudi Arabia
Human platelet antigens (HPA) are implicated in the pathophysiology of certain hematological
disorders, and as varied distribution of HPA-1 alleles and genotypes were reported for different
countries and ethnic populations, we determined the distribution of HPA-1, -2, -3, -4, and -5
alleles, genotypes and haplotypes for 194 healthy Bahraini subjects by polymerase chain reaction
with sequence specific primers. The distribution of the HPA polymorphisms was in Hardy-Wein-
berg equilibrium. Allele frequencies of 0.76 and 0.24 (HPA-1a and -1b), 0.77 and 0.23 (HPA-2a and
-2b), 0.57 and 0.43 (HPA-3a and -3b), 0.93 and 0.07 (HPA-4a and -4b), and 0.86 and 0.13 (HPA-5a
and -5b) were seen. With the exception of HPA-3a/a (30.4%), the frequencies of homozygous HPA-
1a/a (56.8%), 2a/a (60.1%), 4a/a (87.2%), and 5a/a (75.7%) were higher than those of heterozygous
(a/b) or homozygous (b/b) variants. Our results provide basic information for further studies of
the HPA system polymorphism, which in turn will be instrumental in understanding and treating
immune-mediated platelet disorders. Am. J. Hematol. 82:242–244, 2007.
V V
C 2006 Wiley-Liss, Inc.
Key words: human platelet antigens; PCR-SSP; haplotype; hematological disorders
INTRODUCTION
Human platelets alloantigens (HPA) are complex of
platelet membrane glycoproteins with cell-bound anti-
gens [1]. HPAs are polymorphic, with many biallelic var-
iants identified [1], and single nucleotide substitution
within HPAs yields the a and b alleles [2]. These were
implicated in the pathogenesis of pathological condi-
tions, including ischemic stroke and cerebrovascular dis-
eases. The distribution of HPA genotypes is geographi-
cally and ethnically restricted. The prevalence of HPA-
5b and HPA-2b is high among Africans [3] but very low
among Asians [4,5], while the frequency of HPA-1b is
higher among Caucasians [6] and Berbers [7] than Asians
[4,5]. In so far as data on the distribution of HPA poly-
morphisms among Arabs are scanty, the present study
investigated the diversity in HPA alleles, genotypes, and
haplotypes in Bahrain, an island kingdom located in the
Arabian Gulf. This study provides basic information for
further studies of the HPA diversity and will serve as ref-
erence for anthropological studies, and for studies of
associations between HPA polymorphisms and disease.
MATERIALS AND METHODS
Study Subjects
Study subjects comprised 194 Bahraini healthy sub-
jects (102 males, 92 females, mean age: 27.7 ± 15.2
years). Participants were considered healthy accord-
ing to clinical history and laboratory examinations,
including complete blood count and hemoglobin elec-
trophoresis. Exclusion criteria included subjects with
a personal and familial history of hemoglobinopathies
and thrombophilias, and non-Arab origin. All partici-
pants were asked to sign a consent form after the pur-
*Correspondence to: Wassim Y. Almawi, Department of Medical
Biochemistry, College of Medicine & Medical Sciences, Arabian
Gulf University, PO Box 22979, Manama, Bahrain.
E-mail: wyalmawi@yahoo.co.uk
Received for publication 7 June 2006; Accepted10 July 2006
Published online in 7 December 2006 Wiley InterScience (www.
interscience.wiley.com).
DOI: 10.1002/ajh.20769
American Journal of Hematology 82:242–244 (2007)
V V
C 2006 Wiley-Liss, Inc.

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pose of the study was explained, and after all institu-
tional ethics requirements were met.
HPA Polymorphism Genotyping
Total genomic DNA was extracted from the pe-
ripheral blood mononuclear leukocytes by the Amer-
sham GFX column methods, according to manufac-
turer’s specification (Amersham, Buckinghamshire,
UK). DNA was dissolved in RNAase-free water, and
stored at 48C pending analysis. HPA polymorphism
was done by the polymerase chain reaction with
sequence specific primers, as previously described [2].
Amplified products were subjected to agarose gel elec-
trophoresis. Allele frequencies were determined using
HLAStat-2000 software, and the frequencies of the
most frequent haplotypes were determined by the
maximum likelihood method. The odds ratio (O.R.)
and 95% confidence interval were also determined.
Analysis was performed with SPSS version 13.0 for
Windows statistical package.
RESULTS
HPA Polymorphisms Analysis
The distribution of HPA-1, -2, -3, -4, and -5 was in
Hardy-Weinberg equilibrium among study subjects
(Table I). Allele frequencies of 0.76 and 0.24 were
seen for HPA-1a and -1b, 0.77 and 0.23 for HPA-2a
and -2b, 0.57 and 0.43 for HPA-3a and -3b, 0.93 and
0.07 for HPA-4a and -4b, and 0.86 and 0.13 for HPA-
5a and -5b (Table I). With the exception of homozy-
gous HPA-3a/a (30.4%), the frequencies of homozy-
gous HPA-1a/a (56.8%), 2a/a (60.1%), 4a/a (87.2%),
and 5a/a (75.7%) genotypes were higher than hetero-
zygous (a/b) or homozygous (b/b) variants (Table I).
The most significant HPA haplotypes encountered
were HPA 1a-2a-3a-4a-5a (haplotype frequency ¼
0.33) and HPA 1a-2a-3b-4a-5a (haplotype frequency ¼
0.20).
DISCUSSION
In view of their association with hematological dis-
orders, coupled with their differential world distribu-
tion, we investigated the prevalence of HPA-1(5 in
Bahrain. To avoid epidemiologic bias, non-Arab Bah-
rainis (Iranians or recently-naturalized Bahrainis)
were excluded. The varied prevalence of the HPA
polymorphisms was consistent with previous reports
documenting the geographical heterogeneity in their
distribution [3,5,6].
The prevalence of HPA-1b (24%) and HPA-2b
(23%) were high among Bahrainis, compared with
Africans [3], Asians [5,8], and Europeans [6], which
was comparable to rates established for Saudi Arabia
[9], Tunisia [10], and North African Berbers [7], sug-
gesting that Arabian Peninsula-North Africa is focus
of HPA-1b. The prevalence of HPA-3b (43%) was
less selective, as prevalence rates among Bahrainis
were comparable to Asians [5,8] and Europeans [6].
Although virtually absent from Europeans [6] and
Asians [5,8], HPA-4b was present in lower frequency
(7%) in Bahrain, and in neighboring Saudi Arabia [9].
Although the highest frequency of HPA-5b was
reported in Africa (18.2–26.8%; 3) and Italy (23%),
the frequency of HPA-5b in Bahrain (13%) was com-
pared with Saudi Arabia [9] and UK [6], but higher
than those seen in Asians, where 2–5% frequencies
were reported [5,8].
Although the prevalence of HPA-3b and HPA-4b
in Bahrain overlap those observed for several ethnic
groups, our results indicate that HPA-1b and 2b al-
leles are common among Bahrainis. The frequency of
HPA-5b among Bahrainis appears to be closer to
northern African and Saudi frequencies. Although
implications of our findings remain speculative at this
stage, they add up to the existing body of literature on
HPA system diversity and will aid in determining the
risk of hematological disorders in the population
studied.
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TABLE I. HPA Allele and Genotype Frequenciesa
HPA
Allele
frequency
Genotype
frequencyHardy–Weinberg
ABA/AA/BB/B
x2
P valueb
HPA-1
HPA-2
HPA-3
HPA-4
HPA-5
0.760
0.767
0.568
0.932
0.861
0.240
0.233
0.432
0.068
0.132
0.568
0.601
0.304
0.872
0.757
0.385
0.331
0.514
0.122
0.209
0.047
0.068
0.176
0.000
0.027
0.467
0.810
0.401
0.179
1.040
0.495
0.368
0.527
0.672
0.308
aStudy subjects comprised 194 Bahraini healthy subjects.
bPearson’s x2test.
243Brief Report: HPA1-5 Gene Polymorphism in Bahrain
American Journal of Hematology DOI 10.1002/ajh

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American Journal of Hematology DOI 10.1002/ajh