Status of erythrocyte genetic disorders in people of desert and humid environments in Rajasthan, India: focus on natural selection in tribals against malaria

Abstract

In India, Rajasthan is the largest state having two distinct environments separated by presence of Aravali Mountains. One is desert, located in the west region and other is humid in the east region where malaria is endemic. In Rajasthan, various inherited erythrocyte genetic disorders, abnormal haemoglobins (Hbs), thalassaemia (thal) and glucose-6-phosphate dehydrogenase enzyme deficiency (Gd) have been extensively studied in people of scheduled tribe (ST), scheduled caste (SC), general caste (GC) and other backward class (OBC) populations residing in both environments. In these populations, abnormal haemoglobin variants, Hb-S, Hb-D, Hb-E, Hb-J, Hb-C and Hb-H in heterozygous (trait) and/or homozygous state with varying incidence have been detected. Among these Hb variants, sickle cell Hb in trait form (Hb-AS) is common and widely distributed in diverse populations. Genes of β-thalassaemia trait (0.0–9.0%) are more prevalent compared to α-thalassaemic (1.88–3.07%) genes and are also widely distributed. Gd disorder is also common in occurrence and widely distributed with varying incidence (0.64–22.0%) in people of both environments. Relatively a high incidence of Hb-S (31.14%), β-thalassaemia (9.00%) and Gd (22.00%) genes reported in tribals of southern Rajasthan. In present communication, status of various erythrocyte genetic disorders in people of both environments, natural selection in tribals against malaria, mitigation and control of these genetic disorders and effect of fluoride exposure in tribals having sickle cell and β-thalassaemic genes are considered and critically reviewed. These findings may be useful in framing and implementation of health policies for the mitigation and control of erythrocyte genetic disorders in tribal communities.