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The anatomy of a gene

Genetic testing has today grown to include a broad spectrum of complex diseases and experts argue the need for it to be made rampantly available, accessible and safe for all.

Published: 21st March 2021 05:00 AM  |   Last Updated: 19th March 2021 10:37 PM   |  A+A-

DNA, Genes

Representational image

Adwitya Shankar (25), has seen a lot of medical tumult in her family. Her father succumbed to lung cancer, brother to testicular tumour, while her sister has breast cancer. Shankar was diagnosed with colon cancer at 23, underwent surgery, chemotherapy, but had a relapse. She is currently undergoing second-line chemotherapy.  

"We were asked to opt for genetic testing to understand our family's heredity better. The result showed TP53 mutation, which is a genetic defect, and it made it imperative to start surveillance of her family members, detect the disease early and treat it accordingly," says Shankar.

The test helps make a genetic kundali to assist doctors in ascertaining a patient’s disease ancestry and take preventive steps. The discipline has grown from a niche speciality for rare disorders to a broad scope of applications in personalised health solutions and precision medicine. 

Decoding genes

Dr G Arun Kumar, Scientific Affairs Manager, MedGenome Labs, Bengaluru, likens the genome as the instruction book in the body, which exists in multiple volumes, genes as the individual pages, and DNA as these books' language.

"We inherit two copies of every gene, one from each parent. Sometimes, multiple genes are required to control one function, while at other times, just one gene may influence multiple functions. The DNA sequence of a gene is the code that instructs the cell to make proteins. These proteins, in turn, impact all bodily functions," he says, adding, "Variations in the DNA sequence can disrupt the protein it encodes and put us at risk of acquiring certain diseases. Genetic testing is required to detect such variants."

Genetic tests are also commonly called DNA testing. "These tests can confirm or rule out disease, predict risk for disease, and assess the possibility of passing on abnormal genes to offspring. Depending on the purpose of testing, it could be molecular testing, chromosomal testing, biochemical testing, or whole-genome sequencing," says Anu Acharya, CEO, Mapmygenome. 

Test it right

Calling genetics the basic science of medicine, Dr Divya Agarwal, Consultant, Genetics, Max Hospital, Gurugram, and Advisor, Life Cell Labs, Delhi, says, "Genetic disorders are just under-diagnosed because of certain misbeliefs.  First is the lack of awareness, not just among the public but also among doctors. Even a doctor/specialist wouldn't think of genetic aetiology in the first place. More often than not, it is the diagnosis of exclusion. Secondly, people assume that these tests are expensive and not readily available, which is no longer the case."

The patient, their family, geneticist, molecular pathologist, and genetic counsellor face different challenges, shares Dr Siddharth Srivastava,  Chief Scientist (Molecular Oncology), Neuberg Center for Genomic Medicine, Ahmedabad.

"Genetic testing can be done through either the blood or tissue sample. Usually, the results are out in about 10 days. A patient should understand the report from the treating doctor and if necessary, consult the molecular pathologist and a genetic counsellor," he says.

Disease diary

Approximately 6,000 genes are known to cause human disorders. The genetic basis of most complex diseases is being identified every passing day. "Genetic testing can help detect inherited disorders such as Down's syndrome, thalassemia, haemophilia, Duchenne muscular dystrophy and spinal muscular atrophy (SPA). Genetic testing is also used in prenatal diagnosis, recurrent abortions, infertility, and others. In complex diseases such as cancers, genomic testing can diagnose and offer better treatment options," says  Dr Udhaya Kotecha.

This kind of testing helps people make better choices. For instance, genetic screening helped doctors diagnose that a girl had SPA. "Her parents raised Rs 16 crore for her treatment with a new gene modifier drug. Early testing offers an early intervention," says Dr Gurudutt Bhat, Consultant, Paediatrics, Fortis Hospital, Kalyan, Maharashtra.

Looking ahead

Genome sequencing has undergone tectonic changes in the last decade. "Superior technology and informatics tools have improved the genome sequencing precision and has contributed to a 100-fold reduction in the cost of sequencing," says Dr Kumar. Now there is a need for making genetic diagnosis available, accessible and safe for all.

Gene wise

Genetic testing, also known as DNA testing, identifies changes in chromosomes, genes, or proteins. There are several genetic tests in the market, and the purpose of these tests solely depends on the case. 

THE TESTING METHODS

  • Molecular genetic tests: Single gene or short lengths of the DNA variations are identified that can lead to a genetic disorder. With the recent advancements in the genetic testing space, platforms like the Next Generation Sequencing allow individuals to have access to Whole Genome or Exome Sequencing.

  • Chromosomal genetic tests analyse whole chromosomes or long lengths of DNA to see if there are large genetic changes, such as an extra copy of a chromosome, that cause a genetic condition.

  • Biochemical genetic tests study the amount or activity level of proteins; abnormalities in either can indicate changes to the DNA that result in a genetic disorder.

Did you know?

  • One's DNA is composed of more than three billion base pairs. Collectively, these pairs are called the genome. A portion of the genome is called the exome, which is the protein-sequencing region of one's DNA.

  • In 2006, the cost of sequencing one's genes was around USD 14 million. Less than 10 years later, in 2015, that figure was approximately USD 4,000. By the end of the same year, costs were as low as USD 1,500.

  • There are constant updates in the field of genetics. New data, scientific associations and large-scale studies are published frequently, which increase knowledge on various conditions, helping the community diagnose and prevent conditions from being passed on to the next generation. 

(Source: Arun Kiran P, Lead Genetic Counsellor, Prenetics Limited, a genetic testing and digital health company)

How the benefits far outweigh the costs

Predictive genomic testing is more like an investment plan; the earlier you start, the more benefits you derive. They cost a fraction of some of the modern treatment fees and amount cumulatively spent on regular health check-ups.

The benefits are that it becomes easier to switch to a healthy lifestyle. It prevents or delays the onset of disease. One can manage lifestyle conditions such as diabetes. It helps your doctor choose the best treatment plan for you. Molecular diagnostic, on the other hand, helps in confirming the diagnosis. 

Uses of genetic screening/testing  

  • To find your genetic risk for a disease, which can help you in preventing or delaying the onset of disease

  • To find your risk of passing on some genetic conditions to your offspring

  • To screen your baby or foetus

  • To confirm a clinical diagnosis

  • To understand disease biology and inheritance patterns

  • To determine the best treatment and management plans for a disease

  • To personalise your nutrition and fitness plans

  • To understand your genetic roots and ancestry

  • To understand what makes you unique and possibly eccentric

(Source: Anu Acharya, CEO, Mapmygenome) 
 



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