Haematological and Molecular Characterization of Sickle Cell-β Thalassemia in Southern Belt of Khyber-Pakhtun-Khwa, Pakistan

Sickle cell-β thalassemia (HbS-β thalassemia) is an inherited erythrocyte disorder affecting multiple organs. It results from compound heterozygosity for sickle cell trait and β thalassemia trait. As individuals are living well into middle age due to advances in diagnosis and treatment, further disease-related complications are coming into light. The present study was undertaken to determine the genetic factors responsible for hematological and molecular variability of HbS-β thalassemia patients in Southern belt of Khyber-Pakhtun-Khwa (KPK), Pakistan. The study was designed to analyse both molecular and haematological characterization of HbS-β thalassemia patients using Hb electrophoresis and allele specific primers through polymerase chain reaction (PCR) to determine both α and β-thalassemia, and restriction enzymes for characterization of γ-globin gene arrangement. A total of thirty-two HbS-β thalassemia cases with variable clinical manifestations were investigated. Twenty-four patients showed milder clinical presentation against eight patients who had severe clinical manifestations. Six β thalassemia mutations were identified: IVS 1-5 (Gu003eC), codon 8/9 (+G), codon 30 (Gu003eC), Cap+1 (Au003eG), -88 (Cu003eT) and Codon 41/42 (-TCTT). Codon 30 (Gu003eC) and -88 (Cu003eT) mutations were found only in Pashtoon ethnic group while Cap+1 (Au003eG) mutation was observed only in Balochi ethnic group. Interestingly, eleven HbS homozygous patients, all in Pashtoon ethnic group were observed for the first time in Pakistan. Both α thalassemia and XmnI polymorphism in homozygous condition (+/+) were found to be common among the milder cases. The βS chromosomes were linked to the typical Arab-Indian subcontinent haplotype. Saudi haplotype is mostly associated with HbS and haplotype III is found only with Pashtoon ethnic group. The phenotypic expression of HbS-β thalassemia is not uniformly mild and α thalassemia and XmnI polymorphism in homozygous condition (+/+) are additional genetic factors modulating the severity of the disease in the Pakistan.