α-Thalassemia syndromes in the United Arab Emirates.

α-Thalassemia (α-thal) is usually due to deletions within the α-globin gene cluster, leading to loss of function of one or both α-globin genes. α-Thalassemia is prevalent in the Arabian Peninsula, particularly in the United Arab Emirates (UAE) and Saudi Arabia. There are no large-scale reports regarding the prevalence of α-thal in the Arabian populations apart from sporadic surveys in the mid-1980s on red cell indices from Saudi Arabia and a more recent study from Kuwait. Several studies were conducted in an attempt to elucidate the frequency of α-thal in the UAE. Cord blood samples were collected from 419 consecutive newborns of UAE national mothers. The study involved polymerase chain reaction (PCR)-based analysis of the α-globin genes and sequencing using an ABI Genetic Analyser 3130. The findings demonstrated that 49% of the neonates had α-thal, one of the highest in the world. The incidence of α-thal, particularly the -α(3.7) deletion, was extremely high. The distribution of mutations was extensive, ranging from the simple -α(3.7) genotype to severe nondeletional type α-thalassemias such as the polyadenylation signal (polyA1) [α(PA-1) (AATAAA>AATAAG)], polyA2 [α(PA-2) (AATAAA>AATGAA)], Hb Constant Spring [Hb CS, α142 (α(CS)α/α(CS)α) TAA>CAA (α2)] and pentanucleotide deletion [α(-5 nt) (GAGGTGAGG>GAGG)]. The nondeletional mutations, denoted α(T)α or αα(T), are markedly frequent in the UAE and are well characterized. The report here describes the analysis of 84 chromosomes having deletional and nondeletional types of α-thal. Of the 84 chromosomes, 47.4% had the polyA1 mutation (α(PA-1)α), 28.2% had the small deletion -α(3.7), 11.5% had Hb CS (α(CS)α), and 5% were positive for the pentanucleotide deletion (α(-5 nt)α). These findings show that nondeletional α-thal has a significant impact on the genotype/phenotype correlation in the UAE. It is important to note that the polyA1 mutation accounted for almost 50% of all the α-thal alleles, making it one of the most common mutations in the Gulf Region.