Diabetes-free desert tribe intrigues researchers
doi:10.1038/nindia.2015.23 Published online 18 February 2015
A study of the DNA of a nomadic tribe inhabiting the Thar desert of Rajasthan has overthrown a prevalent notion about the association of certain genes with diabetes1.
Called Raikas, the physically active tribe belongs to a camel rearing community in whom the prevalence of diabetes is almost zero prompting immunologists to discover the reasons.
The new study of DNA samples of this unique group of people has sprung a surprise. The researchers found that their DNA contains a very high frequency (53%) of Human Leukocyte Antigen (HLA) gene called HLA-DRBI*03 which shows a remarkably high association with the development of Type 1 diabetes (T1D) in almost all populations around the world including the Indian population.
The HLA system consists of genes located on chromosome 6 that encode for proteins on the surface of cells that are responsible for regulation of the immune system. Genes in the HLA system of man confer more than half the genetic risk of developing T1D.
"Our finding is intriguing because the HLA-DRBI*03 allele is known to predispose people to diabetes and other autoimmune diseases (celiac disease, autoimmune thyroiditis) almost uniformly around the world," Narinder Mehra, Dean of research at the All India Institute of Medical Sciences (AIIMS), New Delhi and a corresponding author of the study told Nature India.
"For instance, the people of Sardinia in Italy, a diabetes hotspot, have the highest DRB1*03 allelic frequency of 55.7% and a correspondingly high prevalence of diabetes in the world indicating a strong association of this allele with diabetes," he says.
Similarly in the North Indian population, their earlier studies revealed that the frequency of this gene rises from a mere 16.4% in the healthy population to less than 90% in patients with T1D.Mehra said his group launched the DNA study in the Raikas with the notion that the near absence of diabetes in this community could be explained by the low frequency of diabetes susceptibility HLA genes in this population.
"Instead we found a very high phenotype frequency (53%) of DRB1*03gene. Virtual absence of diabetes in the Raikas despite having a very high frequency of the susceptibility HLA gene is intriguing."
"In my opinion this is an outstanding observation directly linking our genes to diabetes," Seyed Hasnain, Head of Kusuma School of Biological Sciences at the Indian Institute of Technology in Delhi told Nature India.
Explaining the possible reasons for the absence of diabetes in the Raikas, despite the presence of the susceptibility gene, the researchers say they cannot rule out the "possible influence of other protection conferring genes” or an overriding influence of environmental triggers including dietary factors.
According to the researchers, Raikas mainly survive on Bajra (Pennisetum glaucum) grown in their fields and camel milk, drinking at least half a litre daily for 5 days in a week. An insulin-like protein has been detected in camel milk, and clinical trials in 2005 by India’s Bikaner Diabetes Care Research Centre have shown that the daily consumption of 0.5 litre camel milk reduces the need for insulin medication by an average of 30%.
"The beauty of camel milk is that the insulin-like milk protein passes rapidly through the stomach into the intestines for absorption," says Mehra. The other possibility is the consistent exposure of the community to sunlight as a part of their lifestyle. High levels of vitamin D might confer a preventive effect on the development of diabetes.
The researchers say their study highlights the role of the environmental factors, food habits and level of physical activity in the manifestation of disease and calls for further research to "define the gene-environment interaction in the context of a multifactorial disease like Type 1 diabetes."