Background: Tribal communities in India constitute a major part of the population and are vulnerable to many erythrocytic hereditary and haematological disorders such as haemoglobinopathies. Genetic studies so far undertaken on tribal groups are scanty, patchy and incomplete. No field-based systematic studies of hereditary haemolytic disorders in Orissa are available. Further, the extent of haemoglobin variants among the tribals in the state is not known. The present study was carried out in the Bhuyan and Kharia tribes of Sundargarh district in Orissa.
Aim: This study aims to find the prevalence/spectrum of haemoglobin variants in two major tribal groups, namely Bhuyan and Kharia and their subgroups, inhabiting the Sundargarh district in north-western Orissa.
Subjects and methods: Following the probability proportionate to size cluster sampling procedure for villages, a randomized sampling procedure was adopted irrespective of the age, sex and individual susceptibility pattern, selecting exclusive villages of each sub-group of tribes in five blocks. A total of 1603 blood samples of 836 Bhuyan and 767 Kharia tribals were screened for haemoglobin variants in the Sundargarh district of Orissa. Laboratory analyses of blood samples were carried out following standard procedures.
Results: The study showed a high prevalence of haemoglobin variants in the Bhuyan (9.8%) and Kharia (13.3%) tribes, sickle-cell disorders contributing 2.4% and 5.6%, respectively. The sickle-cell gene was found to be completely absent in the Dudh Kharia tribe, whereas the frequency in the Dhelki Kharia was quite high (12.5%). For the first time, 1.4% prevalence of haemoglobin E disorders (10 traits and one disease case) was recorded in a tribal population, i.e. Delki Kharia in Orissa. No other haemoglobin variant except beta-thalassaemia trait was detected in the Dudh Kharia tribe (8.1%), showing their genetic isolation (p < 0.001) from the Delki Kharia (4.1%), the average being 6.3% in the Kharia tribe. Out of three subgroups of Bhuyan studied, the sickle-cell trait was detected only in Paraja (0.9%) and Paik (7.4%), and not in Paudi (Hill) Bhuyans. However, the beta-thalassaemia trait was detected in an average 6.5% in the Bhuyan tribe: in Paudi (2.1%), Paik (7.8%) and in Paraja (12.7%). For the first time in the tribes of Orissa a family was found with haemoglobin D trait (in Paik Bhuyan) and another with hereditary persistence of fetal haemoglobin (in Paraja Bhuyan). Clinical and haematological features of these disorders were similar to those reported in previous studies carried out in India.
Conclusion: Isolates of the Bhuyan and Kharia tribes show intra-group variations in prevalence of haemoglobin variants due to founder effect, genetic drift, and the practice of inbreeding in varied geographical and ecological niches in the Sundargarh district of Orissa.