Unravelling the Complexity of the +33 C>G [HBB:c.-18C>G] Variant in Beta Thalassemia.

The +33 C>G variant [NM_000518.5(HBB):c.-18C>G] in the 5' untranslated region (UTR) of the ß-globin gene is described in the literature as both mild and silent, while it causes a phenotype of thalassemia intermedia in the presence of a severe ß-thalassemia allele. Despite its potential clinical significance, the determination of its pathogenicity according to established standards requires a greater number of published cases and co-segregation evidence than what is currently available. The present study provides an extensive phenotypic characterization of +33 C>G using 26 heterozygous and 11 compound heterozygous novel cases detected in Cyprus and employs computational predictors (CADD, RegulomeDB) to better understand its impact on clinical severity. Genotype identification of globin gene variants, including α- and δ-thalassemia determinants, and rs7482144 (XmnI) was carried out using Sanger sequencing, gap-PCR, and restriction enzyme digestion methods. The heterozygous state of +33 C>G had a silent phenotype without apparent microcytosis or hypochromia, while compound heterozygosity with a ß+ or ß0 allele had a spectrum of clinical phenotypes. Awareness of the +33 C>G is required across Mediterranean populations where ß-thalassemia is frequent, particularly in Cyprus, with significant relevance in population screening and fetal diagnostic applications.

The molecular spectrum and distribution of haemoglobinopathies in Cyprus: a 20-year retrospective study.

Haemoglobinopathies are the most common monogenic diseases, posing a major public health challenge worldwide. Cyprus has one the highest prevalences of thalassaemia in the world and has been the first country to introduce a successful population-wide prevention programme, based on premarital screening. In this study, we report the most significant and comprehensive update on the status of haemoglobinopathies in Cyprus for at least two decades. First, we identified and analysed all known 592 ß-thalassaemia patients and 595 Hb H disease patients in Cyprus. Moreover, we report the molecular spectrum of α-, ß- and δ-globin gene mutations in the population and their geographic distribution, using a set of 13824 carriers genotyped from 1995 to 2015, and estimate relative allele frequencies in carriers of ß- and δ-globin gene mutations. Notably, several mutations are reported for the first time in the Cypriot population, whereas important differences are observed in the distribution of mutations across different districts of the island.

The Molecular Basis of α-Thalassemia in the Qatari Pediatric Population.

α-Thalassemia (α-thal) is widely reported in the Arabian Peninsula as one of the main causes of asymptomatic microcytic hypochromic red blood cells with or without anemia in the pediatric population. This is the first study that provides information about the molecular basis of α-thal in the Qatari population. Qatari school children between the ages of 5 and 15, exhibiting laboratory findings suggestive of microcytic anemia were pooled, and those with a mean corpuscular volume (MCV) of <80.0 fL and a hemoglobin (Hb) electropherogram that ruled out ß-thalassemia (ß-thal), were narrowed down to a group of 127. This group was screened for the -α(3.7) (rightward) deletion, and the α(-5 nt), α(polyA1) (α(T-Saudi)), α(polyA2) mutations. A second group of randomly selected Qatari individuals was also screened in order to determine the population's allele frequency for the -α(3.7) deletion. Thirty-nine point four percent of the individuals with microcytic hypochromic anemia were positive for the -α(3.7) deletion (heterozygotes 30.0%, homozygotes 9.4%), 2.6% were positive for the α(polyA1) deletion and 0.8% positive for the α(-5 nt) mutation. None of the children exhibited changes in α(polyA2). Analysis of the random samples determined that 26.4% were heterozygous and 4.5% homozygous for the -α(3.7) deletion with a 17.7% allele frequency. Our results suggest that a significant number of the Qatari pediatric population with microcytic hypochromic anemia are carriers of α-thal mutations. However, 45.6% of the children failed to exhibit any of the above four mutations tested. This suggests the possibility of other mutations in the Qatari pediatric population that are yet to be elicited.