Scientists' strong Recommendation

Go for genetic screening before getting married.

And try to avoid marriages within the same  families, castes and communities if possible!

Genetic testing tells the mutations people are likely to have in order to prevent the disease causing genes carry forward to the next generation. Then try to match your genetic horoscopes, not astrological ones which are useless (2).

Because...recent research says (1)...

As people in South Asia tend to get married within their own castes, the region becomes a living lab  for diseases! Caste groups have a high vulnerability for ‘population-specific’ diseases. A recessive disease is one that can be passed down through families. 

According to the research done by CCMB (Hyderabad, India) scientists,  the Vaishya community have a 100-fold higher rate of butyrylcholinesterase deficiency, a condition of not being able to assimilate the anaesthetic drug than other groups, Rajus (Andhra Khsatriyas) have high risk of cardiomyopathy which effects heart muscle and Reddys in specific geographic location in the state suffer arthritis. 

Likewise Gujjars of Rajasthan, Baniyas of UP and Pattapu Kapus of AP have got high IBD (Identity-by-descent) score that shows they carry certain gene mutations responsible for diseases to future generations. Scientists say that due to Endogamy and marriage in the same caste groups, for instance for the past 108 generations in Vaishya, and in general in the past 2,000 years due to development of castes the disease causing mutations are carried forward to future generations. Out of 80 groups identified for having high IBD score around 14 groups have an estimated size of over 10 lakh population.

Every person in the world not only in South Asia carriers several mutations that if they occurred in two copies would lead to serious recessive diseases. In South Asia ‘founder events’ (loss of genetic variation where small numbers of ancestors carrying mutations give rise to large number of descendants) combined with endogamy (marriage within groups) cause the mutations to often be carried in two copies. In South Asia as due to these two factors it lead to far higher rate of population specific diseases than elsewhere in the world.

South Asians should be viewed not as a single population but as thousands of distinct groups reinforced by cultural practices that promote marrying within one’s community. Although recent changes to cultural norms have resulted in more marriages between members of different groups like castes or subcastes, especially in some urban areas, gene flow between populations was restricted for millenniums. Marriage within a limited group, or endogamy, has created millions of people who are susceptible to recessive diseases, which develop only when a child inherits a disease-carrying gene from both parents. This means that the mother and father must both pass one abnormal copy of the gene to the child in order for the child to develop the disease. A parent who silently carries an abnormal copy of the gene is called a carrier.

Data was analyzed from more than 2,800 individuals belonging to more than 260 distinct South Asian groups organized around caste, geography, family ties, language, religion and other factors. Of these, 81 groups had losses of genetic variation more extreme than those found in Ashkenazi Jews and Finns, groups with high rates of recessive disease because of genetic isolation.

Dr David Reich of Harvard Medical School and Broad Institute in US along with other collaborative authors devised an algorithm to quantify the measure of the found events in each group based on Identity-By-Descent segments, large stretches of DNA shared from a common founder in the last one hundred generations.

Researchers highlighted the case of Vaishya who are around 30 lakh in population has a founder event that is 1.2 fold stronger than that in Finnish population.

“Vaishya ancestry is a known counter-indication for the use of muscle relaxants such as succinylcholine or mivacurium that are given prior to surgery for anaesthesia purpose. This disease is likely to occur at a higher rate due the lesser genetic variation over generations in the history of Vaishya. The genes that are responsible for production of enzymes which metobolises these anaesthesia drugs are produced low in Vaishya. That is why they are given altered anaesthetic drugs,” he said.

He added, “We haven’t studies in all castes what type of recessive diseases are prevalent but we have analysed the groups that have identity-by-descent factors.”

In previous studies, Dr. Reich, Dr. Thangaraj and colleagues found that social groups in South Asia mixed between around 4,000 and 2,000 years ago. After that, the solidification of India’s caste system resulted in a shift toward endogamy. You can see writ in the genome the effects of this intense endogamy.

Founder effect: When a population originates from a small group of founders that bred only with each other, certain genetic variants can become amplified, more so than in a larger starting population with more gene exchange.

Most people carry some disease-associated mutations that have no effect because they’re present only in one parent’s genes. In an endogamous group, however, it’s more likely that two individuals carry the same mutation from a common founder. If they reproduce, their offspring have a higher risk of inheriting that disease.

Rare conditions are therefore disproportionately common in populations with strong founder events. Among Finns, for instance, congenital nephrotic syndrome, a relatively rare kidney disease, is uniquely prevalent. Similarly, Ashkenazi Jews are often screened for diseases like cystic fibrosisor Gaucher disease.

To measure the strength of different founder events, Dr. Reich and Dr. Thangaraj’s team looked for long stretches of DNA shared between individuals from the same subgroups. More shared sequences indicated a stronger founder event. The strongest of these founder groups most likely started with major genetic contributions from just 100 people or fewer. Today, 14 groups with these genetic profiles in South Asia have estimated census sizes of over one million. These include the Gujjar, from Jammu and Kashmir; the Baniyas, from Uttar Pradesh; and the Pattapu Kapu, from Andhra Pradesh. All of these groups have estimated founder effects about 10 times as strong as those of Finns and Ashkenazi Jews, which suggests the South Asian groups have “just as many, or more, recessive diseases,” said Dr. Reich.

The next step, the authors say, is to map out and study the genetic origins of diseases prevalent in different groups. As proof of concept, they screened 12 patients from southern India for a gene mutation known to cause a joint disease called progressive pseudorheumatoid dysplasia. Of the six people that had the mutation, five instances could be traced to founder effects, and one case could be traced to a marriage between close relatives.

This distinction is important because it’s well documented that marriage between close relatives can increase the possibilities of recessive disease. But many South Asians are not yet aware that they should also look out for genetic risks among broader populations. There’s a tendency to think, ‘This will never happen to me because I will never marry my first cousin’'. “But that’s not what’s happening here, according to the data of this new research.

If recessive disease mutations are cataloged, they could potentially be used for prenatal or premarital screening programs, which can be “immensely powerful. An example of successful genetic cataloging can be found in Dor Yeshorim, a Brooklyn-based organization that screens Ashkenazi and Sephardi Jews for common disease-causing mutations to inform marriage matchmaking. The program is credited with virtually eliminating new cases of Tay-Sachs disease, a neurodegenerative disorder, from these communities.

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. Some scientists think knockouts of almost every single gene in the genome probably exist in India and that it’s unequal to anywhere else.

So  you now know the futility of astrological horoscopes while deciding whom to marry in the Indian context and the importance of genetic horoscope matching.

Now decide for yourself which way to go!

And parents please consider it from a scientific point of view if your son or daughter falls in love and wants to get married to a person from another caste.

Citations:

1. https://www.nature.com/articles/ng.3917

http://www.nature.com/ng/journal/vaop/ncurrent/full/ng.3917.html?fo...

2. http://kkartlab.in/group/some-science/forum/topics/debate-between-s...