25 September 2009
The Indian tradition of marrying within one’s caste or community leads to genetic mutations, thus explaining why certain diseases are concentrated only in a particular pocket of the population in India.
The research paper that restructures the Indian population history carries important findings that have medical implications. That many modern groups of people in India have descended from a small number of people is what scientists technically describe as a “founder event” – a rampant Indian practise of people marrying within small group of people.
Senior scientist with Centre for Cellular and Molecular Biology (CCMB), Kumarasamy Thangaraj says that because of this “high endogamy” within the country, practise that dates back to several thousand years, makes these pockets genetically unique. “Because of this, there may be mutation in the gene that leads to various diseases,” Thangaraj says.
And thus recessive hereditary diseases (single gene disorders that occur when person carries two abnormal or malfunctioning copies of a disease causing gene) are seen among Indians who have descended from a small group of founder individuals. Thalasaemia is a case in point wherein a couple (both carriers) carrying one abnormal and normal gene each pass on the abnormal ones to the child.
Researchers say similar founder events seen in other groups, such as Finns and Ashkenazi Jews are well known to increase the incidence of recessive genetic diseases. The new study predicts that the same will be true for many groups in India.
“Further studies of these groups should lead to the rapid discovery of genes that cause devastating diseases, and will help in the clinical care of individuals and their families who are at risk,” said the study’s co–author David Reich, an associate professor of genetics at Harvard Medical School.
Researchers say that there is a certain genetic mutation seen specifically in the Indian sub–continent alone which they have been able to connect with the cardiac condition. “The study gives us an understanding why the incidence of the cardiac disease is different in the Indian sub–continent from the rest of the world,” says Thangaraj. He says there would be similar diseases that can be understood genetically.