Nowadays too many companies are promoting genetic testing. They claim to detect A-Z genetic disorders inside a human body. One of such tests is Genetic Carrier Screening. But what is it actually?
What is Genetic Carrier Screening?
Genetic Carrier screening or simply called Carrier Screening is a genetic test to identify a genetic disorder by screening for mutations or chromosomal abnormalities. It can be done before or during pregnancy to avoid the birth defect of an unborn child . It also determines whether a healthy person is a carrier for a recessive genetic disease or not. The screening test predicts the couple’s pregnancy risk of having a child with genetic disease.
Carrier Screening Test is generally carried out with simple blood test (drawn from the arm). Blood can be taken for a single partner; both the partners and also for the baby (depend on pattern of disorder). This test mainly focus on single gene disorders (monogenic disease). Over 10,000 monogenic human diseases have been identified but only very few are possible to screen during this process. India is the 6th largest country in terms of the population size [1.21 billion as per Census India data)] and due to large population size and high birth rate, birth defects (genetic disorder) are also very common in India. There medical attention is required at a high priority level.
Genetic Carrier screening is the most scientific approach for an early detection or prediction of a hereditary disease. It helps to identify the carrier parent who is bearing the lethal gene but remains unaffected or symptom less as an individual and can predict the chances of having affected baby. (Health Council of The Netherlands 1994). Family genes are very influential. Various genetic disorders pass on to children through their parents or grandparents and are found in the family lineage. A recessive genetic disease does not affect a child with symptoms if the child is bearing a single copy of the defective gene (mutation), however, symptoms are expressed when the
mutation is present in both genes (one gene inherited from the mother and the other from the father).
Genetic Carrier Screening: Why to go for?
Genetic disease is the leading cause of infant death in India. According to Rao and Ghosh (2005), 1 out of every 20 new-borns admitted to the hospital carries a genetic disease and the outcome was nearly 1 out of 10 infant mortality. A study on 2016 stated 20% of infant mortality in the developed countries is caused due to genetic disorders. Consanguineous marriages also increase the risk of congenital abnormalities and genetic disorders. According to the WHO in 2010, an estimated 270,000 deaths during the first 28 days of life were reported due to congenital anomalies globally. Hence it is important to prevent birth defects due to a genetic disorder and create an awareness to reduce the risk of inheritance.
Most of us carry a gene which is causing at least one genetic disorder, although it’s never shown up in a family history. The person carrying this defective gene without suffering any disorder is known as a “carrier” or “carrier person”.
Benefits of the carrier screening concept:
- Normal couples (without genetic disease-bearing gene), can become sure about the reduced risk to their unborn child of developing a genetic disease. Please note that carrier screening does not eliminate 100% of the risk.
- In most cases, if both parents are found to be carriers for the same disorder (but not suffering from the disorder), there is a significantly increased chance of having an affected child and carrier screening will help to make future decisions. As carrier individuals often do not know anything about the disorder, so unknowingly they can pass the defective gene on to their child.
- For couples who are found to be at an increased risk during pregnancy, they can be counseled. Counseling helps to find out a better solution and can avoid an unwanted situation which may harm the couple emotionally.
- A healthcare provider can help to understand the medical options available if a couple is having difficulties to have a baby or query during pregnancy in case of previously having an affected child.
Example of genetic disease
Hemophilia disorder is a good example to explain that an unaffected individual who has the gene that causes hemophilia A (Factor VIII) or hemophilia B (Factor IX) deficiency; having a chance to have a child affected with hemophilia disorder. Factor VIII and Factor IX are needed for the blood to clot normally.
Ideal Time to choose Carrier Screening
Getting tested before pregnancy gives a greater range of options and more time to make decisions.
A carrier parent has a 50% chance of passing the same mutation to the child. If both parents are carriers, the child will have a 25% chance of inheriting both copies of the mutation (one from each parent) to develop the genetic disease.
Genetic disorders mainly express among people with a particular geographic area (basically common in ethnic group). Same ethnic group people often shares genes contains a disease-causing mutation (genetic disease) passed down from ancestory. Consanguinity is a well-known risk factor for genetic disorders including diseases and syndromes that present with intellectual and developmental disabilities. It is important to prevent hereditary diseases that are associated with consanguineous marriage through public education. (ref)
Common Genetic Diseases in India
Few common genetic disorders in Indian ethnicity are Down syndrome, Beta-Thalassemia, Cystic Fibrosis (CF), Sickle Cell Anaemia (SCA), Spinal Muscular Atrophy, Tay-Sachs and Haemophilia A. Indian Genetic Disease Database (IGDD) is the first patient based “genetic disease” database of India and is developed and maintained at Indian Institute of Chemical Biology (IICB). It is very important to understand that genetic diseases cannot be cured; only precaution can be take to prevent/avoid birth defects. Therefore, Carrier Genetic Tests (CGT) is very important to prevent genetic birth disorder.
Is Carrier Screening compulsory?
Genetic Carrier screening test, to be done or not, is a voluntary decision. It can be taken based on a healthy discussion with the partner and other family members. The Indian Government has prepared a Draft Policy (The Hindu Newspaper, Aug 22, 2018). It proposes compulsory genetic screening of all pregnant women to prevent inherited disorders and the title was “Policy for Prevention and Control of Hemoglobinopathies – Thalassemia, Sickle Cell Disease and variant Hemoglobin in India’’. According to the draft note, there are around 36 to 39 million carriers of thalassemia in India and sickle cell disease carriers are about 2.5 million. Almost 1,25,000 patients are affected due to this disease.
On a practical aspects carrier screening test can provide the following information that might be helpful to take a decision:
- If getting pregnant is an issue.
- In case of repeated miscarriages.
For above-mentioned scenarios, both the partners need to be tested initially at chromosomal level. If there is no chromosomal abnormality, then they have to check for gene compatibilities. In some cases, both the partners carry a disease causing mutation in the same gene.
- If the family has a history of a genetic disorder.
Fig 4: Genetic Disorder Traits & the Inheritance Patter (ref)
- If the couple has a previous history of the specially-able children
In such case, the doctor will explain the options are available with the current scenario. Doctor can arrange a genetic counselor to discuss with the couple. It is also important to know the family history for such disorder (reported/unreported).
- A genetic counselor can guide if any reproductive risks and may guide you.
Genetics Counselors fill an important role in patient care and education. Healthcare industries seek Genetic Counselling services to obtain a more complete medical history review, identify potential hereditary risks, review testing options, discuss community resources, review disease management and obtain a guideline to the effects of genetic disorder diagnosis. A counselor primarily meets with patient in-person, however, the availability of genetic counseling is expanding to include phone, video conferencing, and web formats.
Importance of Carrier Screening in India
To prevent Congenital and hereditary genetic diseases a adequate and effective genetic testing facilities and counseling services are most important requirement in India. In urban areas, congenital malformations and genetic disorders are the third most common cause of mortality in newborns. (reference) The practice of marrying within the community poses a higher risk for rare genetic diseases among Indians. According to Union Ministry of Health (TOI, 1st Aug, 2018); a draft policy on ‘Haemoglobinopathies’ has been proposed to focus on current threat of genetic birth defects in India. (Read draft policy here)
Due to various factors such as advance maternal age, marriage with same families, improper lifestyle and many other unknown reasons, India’s genetic structure is prone to have more chances of certain genetic diseases then elsewhere in the world.
With increasing awareness, development of better diagnostic technologies, it has now become easier to detect and prevent fetal and newborn deaths due to genetic abnormalities. But still, a large number of genetic tests are quite expensive and not covered by insurance companies. Till government find a way to regularize Genetic Testing under Insurance policy, or regulates the pricing of tests, India stands a long way from reducing infant mortality from genetic disorders.
So it has become necessary to spread the information to common people so that they may raise a question about their well being to the doctor. Ultimately, it’s your decision to safeguard you and your baby’s health.
If you have any concerns, talk to your doctor today or write to Dr Rochana Ray for a confidential discussion or contact us if you need more information
Related articles : Guide to Non Invasive Prenatal Screening