HLA is the most polymorphic genetic system described in man. It contains several linked loci which encode for cell surface proteins that have an important function in activating immune response after antigenic presentation. New allele variants are frequently being described (i.e.: 1,883 HLA-DRB1 alleles have been recorded by June 2016) [1]. HLA gene frequencies have both a large degree of variability among populations and a striking geographical correlation. These frequencies are useful to infer genetic background and ethnical constitution of modern human groups and also for inferring migrations of ancient ones [2]. In addition, certain combinations of contiguous alleles between HLA neighboring loci show a characteristic frequency due to the robust linkage disequilibrium among them or are distinctive in many extant populations [3]. Also, HLA allele frequencies are unique for studying the origins of relatively homogeneous groups, like the Kurd people living in Iraq. Other HLA gene characteristics are their link to disease and to different responses to drug treatments in patients according to different HLA alleles. Certain HLA alleles affect drug response to treatment in about sixteen different diseases including AIDS [4]. This is important for personalized drug treatment design (including ethnic groups with specific certain high allele frequencies), particularly if other already obtained Kurd HLA results are also included (from Georgia and Iran, in present study) and samples are further increased.
On the other hand, Kurd people live in different countries in the Near East such as Syria, Armenia, Turkmenistan, Kazakhstan, Turkey, Iraq and Iran, the so called Kurdistan ("land of Kurds") (Fig 1, Table 1). Kurdistan is a region placed South Caucasus and North of ancient Mesopotamia. According to genetic studies (like HLA) in Turkish and Kurdish populations, a Anatolian-Mediterranean source for both populations was put forwards; it may be possible that Kurds are initially coming from ancient Hurrians, reviewed in [5,6]. Studies performed with mtDNA and Y-chr have also been done for Kurds, however there is no firm conclusion to infer that most Kurd people have originated either from Middle East and/or from Central Asia [7,8]. Most probably, Kurd people gene pool majority may be composed of an admixture of North Mesopotamian (Caucasus) and Near East peoples; Central Asia gene input is not discarded [5,9,10,11,12,13]. Kurds have mainly been defined by their ancestry, language and cultural uses. Estimations of Kurds number are nowadays between 23 to 41 million people; see Table 1 for numbers and country distribution.
Fig 1. Geographical location of Duhok in the Kurd Autonomous Province of Iraq.
Erbil is province capital and is located about 170 km South East Duhok. (This Fig is similar but not identical to Fig 1 in Ref [13]; It has been included only for illustrative purposes).
In the present paper, a population of Kurds living in North Iraq (Dohuk and Erbil area, North Mosul, Fig 1) has been studied in order to: 1) Determine the HLA class I (A, B and C) and class II (DRB1 and DQB1) allelic Kurd lineages (hereafter “alleles” for simplicity) and specific HLA haplotypes by using standard DNA based techniques, 2) Compare Iraq Kurd HLA profile with those of Central Asia, Siberian, Mediterranean and other World ethnic groups (Table 2) with specific computer programs in order to find out bases of HLA and disease linkage and origins of Kurd people using genetic distances comparisons, Neighbour Joining (NJ) trees and correspondence analyses, 3) obtaining Kurd HLA profile that may be used for preventive HLA Pharmacogenomics and a virtual regional future transplant waiting list among population, and finally 4) Kurd HLA profiles from Tbilisi (Georgia-Caucasus), Iran and Iraq are also compared among themselves.
Table 1. Kurds population around the World [14,15].
Population sample
209 healthy unrelated blood donor volunteers from the cities of Dohuk and Erbil and their area, North Iraq (Fig 1) were class I and class II typed. Unrelatedness and other sample parameters were checked by Drs. R. Al-Qadi and Shadallah Fareq Salih. Erbil is the capital of Iraq Kurdish Autonomous Region placed 175 km southeast Dohuk. The city of Dohuk is located in Kurdistan region in the North of Iraq, 70 km North Mosul and 60 km far from both Sirian and Turkish borders (36°51′00″N 42°59′00″E); Dohuk is historically and continuously inhabited by Kurds since 1000 BC. Dr. Rawand Al-Qadi established at Dohuk General Specialized Laboratory Center has taken samples. Written consent to participate in the present study was signed by each individual. University Complutense Ethics Review Board Committee reviewed and approved this study which was subsequently funded by Ministry of Health and Economy (see Acknowledgments).
All subjects in the study and their grandparents were born in the same area. We compared our data with those of worldwide populations (see Table 2), obtaining genetic distances, relatedness trees and correspondence analyses. Comparisons were done with 7,746 HLA chromosomes.
HLA genotyping
110 Iraq Kurd samples were genotyped for HLA-A, -B, -C, -DRB1 and -DQB1 using Lifecodes HLA-SSO kit, following manufacturer’s suggestions (Immucor Transplant Diagnostic, Inc. Stamford, Connecticut, USA). The rest of the samples (n = 92) were typed using Polymorphism Chain Reaction-Sequence Specific Primers (PCR-SSP) method already mentioned [16]; other methods are now currently used [2].
Table 2. Populations used for this study.
Statistical analysis
Statistical analysis was done with Arlequin v2.0 software [17,18,19]. Frequent complete extended HLA haplotypes were obtained from: 1) HLA loci haplotype frequencies [18,19]; 2) described haplotypes present in other populations [18,19]; and 3) HLA haplotypes if they appeared in more individuals and also the second haplotype was not undefined [18,19]. Reference tables of the 11th and 12th International HLA Workshops were used for comparing phenotype and haplotype frequencies [20,21].
Phylogenetic trees were obtained with the allelic frequencies as described [22,23], using DISPAN programs [24,25]. Correspondence analysis was carried out as described [26]; it displays a general view of the relationships among populations.
HLA allele typing data from Iran Kurds [13] have been converted to low resolution typing data in order to be able to carry out all analyses with as many populations as possible, while relatedness resolution is satisfactory given the very polymorphic HLA system [1].
