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Is your child at higher risk of rare disease? Why more couples are going for genetic tests

Proponents say genetic tests can help couples make their own reproductive decisions armed with information about possible rare disorders. But it comes with an ethical dilemma.

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New Delhi: For centuries, matching janampatris and kundalis, or natal charts, has been an important aspect of the matchmaking process in India. It has been said to determine whether a couple is well-suited. But couples these days are opting for another kind of test to assess their compatibility on a whole other yardstick, all for the love of their unborn progeny.

Indians are said to be increasingly choosing to match their genetic profiles before saying yes to a match.

While gene tests may do little to predict the course of your love story, genetic screening can tell you whether the children born of the union will be prone to any genetic conditions, including rare ones with no known cure yet.

No official estimates are available on genetic testing in India, but industry experts say there has been a rise in the number of people opting for it.

“There is a growing burden of rare diseases in India because most communities have a practice of marrying within their social groups,” said Neeraj Gupta, founder of Genes2Me, a diagnostics laboratory based in Gurugram.

The case of the Nalband gene, where the occurrence of a rare genetic disorder was reported in a Muslim family from the consanguineous (descended from same ancestor) Nalband community of north India, brought the issue to the mainstream in 2015. Six children from the family had presented with a rare disorder.

“Right now, couples mostly come for these tests after marriage, when they are trying to conceive — especially if they have faced issues with pregnancies in the past. But increasingly, we are seeing people from more educated families approaching us for pre-marital genetic tests. And while I think that going forward this could become a regular norm, we are still a long way away from it,” said Gupta.

Priya Kadam, director, reproductive genomics, MedGenome Labs, a genomics and clinical data driven diagnostics laboratory based in Bengaluru, has seen a similar trend.

According to her, at least 4 per cent of the total genetic tests that they carry out are for premarital genetic testing. “Majority of the patients who come for testing are either couples who have previously had children affected with genetic disorder or suffered miscarriages,” said Kadam.

The recessive diseases and disorders that most couples screen for include thalassemia, sickle cell anaemia, cystic fibrosis, spinal muscular atrophy and Hunter syndrome, among others.

Kadam believes that having affordable screening for genetic mutations is the future. Currently, diagnostic tests that look for a specific mutation can cost between Rs 4,000 and 5,000, said Gupta. Preventive genetic screenings, which look for a wider range of mutations, can cost up to Rs 1,00,000.


Also read: New insights into genes that drive cancer: A study of 2,700 samples


Science of recessive disorders

A human being has over 21,000 genes packed into 23 pairs of chromosomes, which are essentially long chains of DNA.

Each gene is made up of a string of pairs of building blocks, or nucleobases — nitrogen-containing biological compounds known as adenine, thymine, cytosine and guanine. It is the sequence of these nucleobases in the gene that determines the proteins that the body creates in order for life to function. The human chromosome has over 3 billion base pairs.

Of the 23 pairs of chromosomes, one pair is the sex chromosome containing up to five per cent of the base pairs that determine all the traits related to one’s sex. The rest determine other characteristics, including whether or not we live a healthy life and which diseases we may suffer from.  

One set is inherited from the mother and the other from the father. Small changes within the gene determine a person’s characteristics — like the colour of their eyes or skin — and these variations in a gene are called alleles. The two alleles in a gene pair are inherited, one from each parent. Now, the characteristics that every allele represents can either be dominant or recessive.

If a child inherits one allele of the dominant trait from one parent, they are likely to express the trait. This explains why most Indians have dark hair — it is an example of a dominant trait in the Indian population. However, if the recessive trait is inherited from both parents, then the child will have the recessive trait.

In most cases, recessive traits lead to harmless changes in physical features. However, in some cases, they could lead to rare disorders. Most rare genetic diseases are a result of a recessive, disease-causing mutation inherited from both parents.

This becomes more likely if the parents share ancestral roots, since there are higher chances of these disease-causing mutations being carried by both in such cases.

The story of the Nalband Gene

In 2015, Mohammed Nazir wrote to the President of India with a “mercy petition”, asking for permission to euthanise his six children. The reason: He could no longer bear to watch them suffering from a rare disease that had no cure.

Upon reading Nazir’s story in the newspaper, researchers from the CSIR Institute of Genomics and Integrative Biology (CSIR-IGIB) in Delhi reached out to him. A team of researchers from the institute found that the children had difficulty balancing their heads and could not sit independently.

They needed help with the most basic tasks, and were prone to episodes of seizures. Based on the clinical characteristics, the researchers made a provisional diagnosis of leukodystrophy — a group of rare, genetic disorders that affect the white matter of the brain.

These diseases damage the brain’s myelin sheath, which acts as an insulator around the nerve fibres in the brain and the spinal cord. Damage to the myelin sheath slows down or blocks messages between the brain and the rest of the body and can cause problems with movement, speaking, vision, hearing and physical development.

The researchers then conducted a full genome sequencing of the children, which helped them identify the disease. Nazir’s children were suffering from a rare mutation in the gene known as the megalencephalic leukoencephalopathy with subcortical cysts 1 (MLC1).

The mutation in the MLC1 gene that the researchers found — described as ‘c.736delA’ — was not found in public databases, but they did find another case of such mutation reported by another team of scientists in Tehran in an Iranian family belonging to a highly consanguineous community.

Similarly, Nazir and his family belonged to the consanguineous Nalband community spread across northern India and Pakistan. “The Nalbands are said to be descendants of Iranian ironworkers who migrated to India with the Mughals. The community is close knit and it is customary for them to marry within the community,” Sridhar Sivasubbu, a scientist at the CSIR-IGIB, told ThePrint.

On identifying the gene, which the team informally referred to as the Nalband gene, the team screened an additional 83 members from the community. Of these, 24 were found to be carriers of the mutation and nine were affected by the disease.

“In order to aid the entire community, we created a polymerase chain reaction (PCR)-based assay for the Nalband mutation for carrier status determination and prenatal screening at an affordable cost,” said Sivasubbu.

“For all these years, we have been in close communication with the community and counselled them about getting themselves screened for the Nalband mutation. Now, some couples approach us for the screening before getting married to check their compatibility.”


Also read: Gene editing might alter our DNA, but at the cost of our humanity


India’s ‘rare’ problem

But leukodystrophy, said Sivasubbu, is only one of the 700 rare genetic diseases that affect over 7,000 individuals in India.

The Indian subcontinent has been a corridor for different migratory waves throughout history. A 2016 genetic study showed that there are four distinct ancestral groups in mainland India, and a separate ancestry in the Andaman and Nicobar Islands.

But the Indian population comprises over 4,000 anthropologically distinct groups that are also sub-classified into tribes and castes. While these different layers of stratification bring a huge genetic diversity among Indians, many of the social groups tend to not marry outside their community. As a result, recessive genetic traits can tend to accumulate within the population.

This may be especially true of areas like Chhattisgarh and Maharashtra, where sickle cell disease, a disorder in which red blood cells become hard, sticky and C-shaped, is known to be more prevalent.

According to Sivasubbu, once their team has identified the gene mutation or allele causing the disease, they no longer need to carry out a full genomic sequencing of every individual to screen for the disease.

India has a huge population, and with the current technology, it is next to impossible to sequence each individual, let alone store all the data.

The solution is to create affordable tests that screen for the particular piece of gene that encodes the disease. This can be done via PCR tests — one of the technologies used to test for Covid too.

The tech enabling genetic testing

Another team at CSIR-IGIB has made the process of genetic testing simpler. A senior scientist from the institute, Debojyoti Chakraborty, made headlines during the pandemic for developing a paper-based test, called ‘Feluda’, that was said to detect Covid within minutes.

The Feluda was based on the team’s earlier work on detecting sickle cell disease. According to Chakraborty, the team’s technology can be used to make similar low-cost, paper-based tests that can screen for a variety of rare genetic diseases, as long as the researchers know the mutation that is causing it.

Meanwhile, the team is already working on new genome editing techniques that can correct genetic disorders in a foetus. “Currently, we are working with diseases that affect the blood — like thalassemia and sickle cell disease,” said Chakraborty.

CRISPR, a well-established gene-editing tool, can be used to correct the genetic disorders that cause blood-related diseases. Chakraborty’s team is now working on ways to carry out genome editing therapies for other diseases as well.

“If a couple is at risk of passing on a serious genetic disorder to their baby, they can try going for IVF procedure, which can help reduce the chances of a baby being born with a genetic disease,” said Chakraborty.

IVF, or In-Vitro Fertilisation, is a procedure where doctors fuse the mother’s egg and the sperm from the father in a petri dish before implanting the embryo back into the mother’s womb. It is primarily used to assist couples who have trouble conceiving naturally.

However, this process can also help identify embryos that are likely to develop rare genetic diseases — although not all disorders can be identified this way.


Also read: Genetic clustering — Economic inequalities seem now in line with regional differences


The ethical dilemma

While pre-marital screening numbers are still low, Kadam said there has been a steady year-on-year rise in demand.

In 2019, CSIR scientists completed an ambitious project of mapping the genes of 1,000 Indians across 55 ethnic groups — an effort that will help identify more mutations linked to genetic disease.

According to Sivasubbu, CSIR-IGIB is also working on developing gene cards. “It will be something like a credit card that can store all your genetic information. The information stored will be private, and only parts of the sequence can be accessed by doctors with the card-holder’s consent.

Meanwhile, Gene2Me has also launched a genetic test that is said to screen for 525 genes linked to diseases like cancer, cardiovascular disorders, neurological conditions, bleeding disorders and metabolic disorders.

The expansion of such tests and projects raises several ethical questions around selective abortions or eugenics. Is it right for parents to abort a foetus if it has a chance of developing a rare genetic disease? And where does one draw the line?

“Usually, these tests are done for severe disorders that are life threatening with several comorbidities. These tests help identify common variations among couples who might already have a child who has been affected by a severe disorder,” said Kadam.

“These tests give more autonomy to couples to make their own reproductive decisions armed with information about their own condition.”

Gupta feels it is a matter of personal choice. “At the end of the day, it is not the parents but the child who has to suffer from the disease,” she said. “Sometimes, the genetic disease is very painful and cruel in nature. It is a very difficult choice, but parents should have all the information to make that choice.”

(Edited by Zinnia Ray Chaudhuri)


Also read: Inter-caste marriages are good for health of Indians. That’s what DNA testing tells us


 

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