β-THALASSEMIA IN ABU DHABI: CONSANGUINITY AND TRIBAL STRATIFICATION ARE MAJOR FACTORS EXPLAINING THE HIGH PREVALENCE OF THE DISEASE

Tribalism and consanguineous marriages are common in parts of the world with a high prevalence of the beta-thalassemia (beta-thal) mutations, and increase the risks of homozygosity for this and other recessive disorders. We explored the frequency of beta-thal genes and beta-thal carriers in 5672 subjects screened before marriage, of whom 2262 were couples. The mean coefficient of inbreeding (F) in the population was estimated from self-reported relationships to prospective spouses in 383 subjects. Overall frequency of beta-thal mutations and beta-thal carriers in the population were 1.16 and 2.3%, respectively. Among the 14 largest tribes, beta-thal carrier frequencies varied from 0 to 13.6%. The estimated F in the population was 0.022. The expected number of couples needed to be screened to detect one couple who were both beta-thal carriers in the non inbreeding (F = 0) and inbreeding (F = 0.022) population was 1858 and 646, respectively. However, among 2262 couples, 10 were both beta-thal carriers, i.e., 1 in 226 couples, significantly (p = 0.02) more than expected by taking only inbreeding into account. Although beta-thal mutations are relatively rare, the burden of beta-thal disease is increased eight-fold by tribalism and consanguinity.