The beta thalassaemia trait in Jamaica.

The objective of this study was to review the prevalence and features of the beta thalassaemia trait in Jamaican populations. Screening of 221,306 newborns over the last 46 years has given an indication of the distribution and prevalence of beta thalassaemia genes, and screening of 16,612 senior school students in Manchester parish, central Jamaica, has provided their haematological features. The prevalence of the beta thalassaemia trait predicted from double heterozygotes was 0.8% of 100,000 babies in Kingston, 0.9% of 121,306 newborns in southwest Jamaica, and 0.9% of school students in Manchester. Mild beta⁺ thalassaemia variants (-88 C>T, -29 A>G, -90 C>T, polyA T>C) accounted for 75% of Kingston newborns, 76% of newborns in southwest Jamaica, and 89% of Manchester students. Severe beta⁺ thalassaemia variants were uncommon. Beta^o thalassaemia variants occurred in 43 patients and resulted from 11 different variants of which the IVSII-849 A>G accounted for 25 (58%) subjects. Red cell indices in IVSII-781 C>G did not differ significantly from HbAA, and this is probably a harmless polymorphism rather than a form of beta⁺ thalassaemia; the removal of 6 cases in school screening had a minimal effect on the frequency of the beta thalassaemia trait. Red cell indices in the beta⁺ and beta^o thalassaemia traits followed established patterns, although both were associated with increased HbF levels. The benign nature of beta⁺ thalassaemia genes in Jamaica means that cases of sickle cell-beta⁺ thalassaemia are likely to be overlooked, and important clinical questions such as the role of pneumococcal prophylaxis remain to be answered.