Molecular Epidemiology of β-Thalassemia in Pakistan: Far Reaching Implications

β -Thalassaemia, an autosomal recessive hemoglobinopathy, is one of the commonest genetically transmitted disorders throughout the world. Collective measures including carrier identification, genetic counseling and prenatal diagnosis are required for preventing β -thalassemia. To achieve this objective, Identification of the spectrum of genetic mutations, especially for various ethnic backgrounds in Pakistan, since the country is a High Burdon Country. Therefore, we designed a cross sectional study to identify the frequency of various gene mutations in different ethnic groups of Pakistan.

Over a period of five years, venous blood samples were collected from 466 individuals belonging to different ethnic groups residing in Karachi, having at least one affected family member known to have β-thalassemia major/ HbE- β-thalassemia/ HbE homozygotes/ β-thalassemia trait. Chorionic villus sampling at 11 to 15 weeks gestational age for 143 couples referred by thalassemia clinics as also used to obtain allele information. In all, 648 mutated alleles were identified. The diagnosis of β-thalassemia trait, β-thalassemia major and Hb E thalassemia were established from clinical data, hematological indices and hemoglobin electrophoresis by cellulose acetate method. DNA was extracted from whole blood for detection of mutations. Primers were designed for simultaneous detection of the following previously described mutations in a single reaction: IVS 1–5 (G-C), Fr 8–9, IVS 1-1 (G-T), Cd-30 (G-C), Cd-5 (−CT), Del 619bp, Cd-15 (G-A), Fr 41–42, Fr 16 (−C) and Cap +1 (A-C) along with two Hb variants: HbS and HbE.

The genetic heterogeneity in Karachi is reflected by the identification of all the common β-thalassemia alleles and two Hb variants but following eight mutations were more common: IVS 1–5 (G-C), Fr 8–9, Del 619 bp, IVS 1-1 (G-T), Fr 41–42, Cd-30 (G-C), Cd-5 (−CT) and Cd-15 (G-A), accounting for 93.9% of the β-thalassemia alleles. However, the distribution was uneven.

Although IVS 1–5 (G-C) was the most common mutation (40.89% of the sample), its frequency varied from 20% in the immigrant (from India) population to 76.9% in the Balochis. The second most frequent mutation was Fr 8–9, constituting 15.7% of the allele pool. Fr 8–9 was the most common mutation in the Pathans (31.3%) as it was in people of Saraikee origin (47%).

IVSI-5 (G-C),(40.89%), Fr8-9(15.7%), & IVSI-I(G-T),(8.17%), were the most common genetic mutations identified in Pakistan. Knowledge of the predominant mutation in a given ethnic group will not only help in developing a short panel of (population-specific) primers of mutations thereby providing a cost-effective method for prenatal diagnosis and also help the clinicians for genetic counseling and pregnancy termination.

No relevant conflicts of interest to declare.