Genotypic-phenotypic heterogeneity of δβ-thalassemia and hereditary persistence of fetal hemoglobin (HPFH) in India

Large deletions in the β-globin gene cluster lead to increased HbF levels by delaying the γ- to β-globin switch process. However, these deletions when inherited as a homozygous condition or when co-inherited with β-thalassemia result in variable clinical phenotypes. Individuals or families with a clinically presenting child, where the parents had HbF levels ≥ 10%, were further screened for the presence of large β-globin cluster deletions. Six deletions in the β-globin gene cluster were screened by GAP-PCR, and the uncharacterized deletions were further analyzed by gene dosage or by multiplex ligation-dependent probe amplification (MLPA). Among 192 individuals suspected for the inheritance of large deletions, 138 were heterozygous for large deletions, 45 were compound heterozygous of a large β-globin cluster deletion and β-thalassemia, and 9 were found to be homozygous for deletions. Among the heterozygotes, the Asian Indian inversion-deletion was found to be the most common deletion (39.9%), followed by the HPFH-3 deletion (30.0%). Other deletions 49.3 kb, δβ-thalassemia (21.2%), and 32.6 kb deletion (4.4%) were also found to be prevalent in our population. Patients compound heterozygous or homozygous for HPFH-3 and 32.6 kb deletions showed a milder clinical presentation, as compared with the patients compound heterozygous or homozygous for the Asian Indian inversion-deletion and 49.3 kb δβ-thalassemia. This comprehensive study highlights the mutation spectrum of large β-globin cluster deletions and the clinical heterogeneity in the patients homozygous or compound heterozygous with β-thalassemia, thus asserting the need for molecular characterization of these deletions.