Haemoglobinopathies and G6PD deficiency among the tribes

Hemoglobinopathies are the commonest single gene disorders in the Indian subcontinent and a high prevalence of these has been observed among Indian tribes. No information was available about these disorders among the tribes of these islands. The Centre undertook studies to assess the prevalence of hemoglobinopathies and G6PD deficiency among the tribes of these islands.

Great Andamanese: A total of 29 Andamanese were screened. All the red cell indices were within normal range. Five persons (14.3%) belonging to two families showed the presence of HbE trait. Increased level of HbA2 suggestive of B thalessemia trait was observed in one child. One female was found to be G6PD deficient.

Onges: The RBC indices of all the 46 Onges examined were within normal limits.  All the Onges were negative for sickle hemoglobin. Hemoglobin electrophoresis showed A, A2 pattern and no abnormal hemoglobins were detected. The Hb A2 and Hb F levels were normal in all the individuals. None of them were G6PD deficient.

Jarawas: None of the 54 samples from Jarawas were positive for sickle cell haemoglobin. Haemoglobin electrophoresis showed A: A2 pattern indicating absence of any abnormal hemoglobin. HbA2 and HbF levels were normal in all the Jarawas tested. None of the samples were found G6PD deficient.

Nicobarese: None of the 128 samples from Nicobarese were positive for sickle cell haemoglobin. HBA2 levels were normal in all except one with HBA2 of 7.29 suggestive of beta thalassemia trait. None of the samples were G6PD deficient. Fetal hemoglobin was found raised in one individual .

In conclusion, the findings of the study indicate that haemoglobinopathies and G6PD deficiencies are not important public health problems among the tribal populations of these islands. This is in spite of the fact that the population strength of most of the population are extremely small leading to high risk of inbreeding.

Genetic affinities of the tribes of Andaman and Nicobar Islands

The Andaman Islands are inhabited by hunter-gatherers of unknown origin, now on the verge of extinction. The Andamanese and other Asian small statured peoples, traditionally known as “Negritoes” resemble African pigmies. However, it is generally believed that they descended from the early Australo-Melanesian settlers of South East Asia and that their resemblance to some Africans is due to adaptation to a similar environment rather than shared origins.

Mitochondrial DNA (mtDNA) sequences and RFLP polymorphysms and Y-chromosome biallelic markers and micro-satellites were analysed in  Onges, Jarawas, Great Andamanese and Nicobarese. It was observed that these tribes exhibit low genetic variability that is consistent with their small population size and reproductive isolation. The data shows that the tribes of Andamans have closer affinities to Asian than to African populations and suggest that they are descendants of early Paleolithic colonizers of South East Asia. In contrast the Nicobarese have genetic affinities to groups widely distributed through out Asia today presumably descended from Neolithic agriculturalists.