It is an anesthesiologist’s job to enquire about the patient’s allergies before doing their job. Somewhere in the south of India, anesthesiologists carry out their job a little differently. Before any procedure, they want to know which regional groups their patients are from.

Medical workers have found that members of regional groups tend to have similar reactions or responses to the medications given to them. It is nothing strange when it comes to Asian cultures, as a lot of importance is given to being associated with a caste, religion – or in this case, a regional group.

For example, medical caregivers from South India discovered that patients with the surname Reddy are most likely to develop a form of arthritis that affects the spine. They have also noticed how patients from the Raju community are most likely to get cardiomyopathy, which is something affecting the heart muscle.

It might be a surprising discovery for medical workers from the rest of world – but, in South Asia, it is understandable since members of a particular religion group tend to marry and procreate within the same group. As a result, the same genes have been flowing from different generations.

South Asia and marriages


India alone has a population of 1.5 billion and has about 5,000 well-defined sub-groups, which makes it one of the most genetically diverse places on this planet. Marriage in the Indian community is deeply rooted in culture and tradition, and only recently marriages between members of different religion groups have started to happen. Recently, it has been found that millions of people are likely to suffer from recessive diseases – due to the endogamy culture that has been practised by their regional group for decades.

According to Kumarasamy Thangaraj, a senior scientist at Hyderabad’s Center for Cellular and Molecular Biology, recessive diseases happen when children inherit disease-carrying genes from both parents. It is why anesthesiologists find it easier to categorise their patients by the religion groups they belong to.

In studies that were conducted on more than 260 distinct South Asian groups, it was found that “81 groups had losses of genetic variation more extreme than those found in Ashkenazi Jews and Finns”. These are the groups that have the highest rates of recessive disease largely due to genetic isolation. Ashkenazi Jews are most likely to have cystic fibrosis or Gaucher disease while the Finns are known for a relatively rare kidney disease, the congenital nephrotic syndrome.

There are about 5,000 anthropologically well-defined groups that can be found in South Asia today. Researchers have been collecting DNA from members of different regional groups for over 15 years and today, they have a rich set of genetic data at their disposal.

The offspring of members from an endogamous group have more chances of inheriting diseases if both of their parents carry the same diseases. Scientists have named this the founder effect, which means that both parents inherited the same diseases from a common founder.

It is how and why rare diseases are found in regional groups specifically groups with very strong founder events. Since it has been discovered that there are about 14 groups with estimated census sizes of over one million in South Asia, the founder effects are about 10 times as strong and relevant as the Finns and Ashkenazi Jews groups.

Studies for a better future


This data has prompted scientists to take things to the next level by analysing further the genetic origins of predominant diseases in different groups. They also hope to bring more awareness on how marrying close relatives can increase the chances of recessive disease. According to a geneticist at Harvard Medical School, Dr. Reich, there’s a huge, untapped opportunity to do biological and genetic research in South Asia.

An author of the paper and a post-doctoral researcher at Columbia University, Priya Moorjani, thinks that all these studies regarding recessive disease mutations will come to great use for prenatal or premarital screening programs. Screening programs are meant for marriage matchmaking to help eliminate common disease-causing mutations from the same communities.

Alan Shuldiner, a professor of medicine at the University of Maryland and genetics researcher for Regeneron Pharmaceuticals, remarked that “scientists often try to manipulate, or knock out genes in mice or flies to better understand human disease.”

“But populations like those found across South Asia provide a powerful opportunity to study how gene changes manifest naturally in humans. These are “genetic experiments of nature that have occurred across the planet.” MIMS

Read more:
Revisiting the Human Genome Project and other health studies for a more holistic view of genetic diseases
Project to synthesise human DNA creates tension after public announcement
Why do some people have immunity to the world’s major diseases?

Sources:
https://www.nytimes.com/2017/07/17/health/india-south-asia-castes-genetics-diseases.html
https://www.genomeweb.com/microarrays-multiplexing/south-asia-population-study-highlights-founder-events-recessive-disease
https://medicalxpress.com/news/2017-07-south-asian-genomes-boon-disease.html