Sickle cell disease in the Kurdish population of northern Iraq

Epidemiological studies have revealed that sickle cell disease patients are clustered in two geographical areas in Iraq, one among the Arabs in the extreme south, another among the Kurdish population in the extreme north, where they constitute major health problems. However, no studies have focused on the genotypes responsible for sickle cell disease or the β-globin gene haplotypes associated with it. For the latter purpose, a total of 103 unrelated Kurdish sickle cell disease patients were evaluated by restriction fragment length polymorphism (RFLP) for the sickle cell mutation, followed by multiplex polymerase chain reaction (PCR) and reverse hybridization for β- and α-thalassemia (β- and α-thal) mutations, whenever indicated. Results showed that the most common genotype was sickle cell anemia (68.0%) followed by Hb S/β(0)-thal and Hb S/β(+)-thal at frequencies of 24.2 and 7.8%, respectively. Eight β-thal mutations were associated with the latter two genotypes including: IVS-II-1 (G>A), IVS-I-110 (G>A), codon 8 (-AA), codon 44 (-C), codon 22 (-7 bp), IVS-I-1 (G>A), codon 30 (G>C) and IVS-I-6 (T>C). In Hb SS patients, the -α(3.7) deletion was documented in 10.0% and was the only α-thal mutation detected. Furthermore, 5' β-globin gene cluster haplotyping of 128 β(S) chromosomes revealed that the most common haplotype seen in 69.5% was the Benin haplotype, followed by the Arab-Indian haplotype in 12.5%. These latter findings closely resemble reports from neighboring Turkey, Syria, Jordan, Lebanon and Mediterranean countries, suggesting a possible common origin, but are in contrast to findings from the Eastern Arabian Peninsula and Iran.