Diversity of sickle cell trait in Jharkhand state in India: Is it the zone of contact between two geographically and ethnically distinct populations in India?

Incidence of sickle cell trait in India is high in peninsular south, south-eastern, central and south-western India, while in north and north-eastern India, it is absent. Unicentric origin of SCD in the tribals of nilgiri hills in southern India has been proposed. The present study on the frequency of HbS trait and beta-globin gene haplotypes was conducted in the tribal-rich states of Chhattisgarh and Jharkhand to get an insight into the uneven distribution of HbS in India. Jharkhand borders with the HbS-high Odisha and Chhattisgarh, and HbS-low UP, Bihar and Bengal. Cellulose acetate gel electrophoresis was performed on the collected blood samples, to detect sickle haemoglobin (HbS) followed by DNA analysis. HbS associated beta-gene haplotype was constructed for the samples positive for HbS and all the tribals by PCR-RFLP. Out of 805 (Chhattisgarh - 261, Jharkhand - 544; greater than 36 percent tribals) samples analysed HbS frequency was 13 percent in Chhattisgarh and 3.3 percent in Jharkhand. Within Jharkhand, frequencies varied considerably from 10 percent in Tatanagar to nil in Sahibganj. The Arab-India (AI) haplotype of beta-globin cluster occurred in low frequency, confined mainly to Chhattisgarh. The most abundant haplotype in all the populations was the East Asian, + - - - - - +, rare in HbS, mainly in Sahibganj in east Jharkhand, which lacked AI. Our results indicate that besides the heterozygote advantage againstmalaria, the uneven regional distribution of HbS trait is because of restricted movement of two different populations, Dravidian from the south and Tibeto-Burman from the east into the Indianmainland which failed tomeet, we conjecture, due to severe climatic conditions (deserts and heat) prevailing through parts of central India. Apparently, Jharkhand became a zone of contact between them in recent times.