FREQUENTLY ASKED QUESTIONS
What are genes?
Genes are a unit of heredity which is transferred from parents to the offspring and determine the characteristics/traits of the offspring. They are made up of DNA which gives a set of instructions to make molecules called proteins.
What are inherited genetic disorders?
A genetic disorder is a genetic problem caused by one or more abnormalities in the genome, especially a condition that is present from birth. Some of these are passed on from the parent to the offspring and are called inherited genetic disorders.
How are these disorders inherited?
Every person has two copies of each gene, one inherited from each parent, in the case of autosomal genes. In case of autosomal dominant disorders, one mutated copy of the gene is enough to cause the disease phenotype. Thus the probability of inheriting the disorder for the offspring is 50% e.g. Marfan syndrome. However, in an autosomal recessive disorder both the copies of the gene have to be defective to manifest the disease phenotype. Based on the affection status of the parents, the chances of the child inheriting the disorder may vary. If both the parents are phenotypically normal carriers, the child has a 25% chance of inheriting the disease, a 25% chance of being normal and a 50% chance of being a phenotypically normal carrier. Thalassemia is inherited in an autosomal recessive pattern, which means both copies of the HBB gene in each cell have mutations. This may be inherited from a phenotypically normal parent or occur de novo in the offspring.
What are some common inherited genetic disorders??
The most common inherited genetic disorders are beta-thalassemia, haemophilia, sickle cell anaemia, spinal muscular atrophy, cystic fibrosis, deafness, inborn errors of metabolism, wilson’s disease, duchenne muscular dystrophy, growth hormone deficiency, congenital adrenal hyperplasia, retinitis pigmentosa, etc.
What is the Carrier Screening Test?
The Carrier Screening Test is a screening test to find out whether you or/and your partner carry any genetic defect that could cause an inherited genetic disorder in your baby. This is useful in recessive diseases only.
Why should one take the Carrier Screening Test?
The Carrier Screening Test can help a couple predict their chances of having a baby with a recessive disorder.
When should the carrier screening be taken by a couple?
This test should ideally be carried out during pre-conception, when the couple is planning a pregnancy.
In what situations is the carrier screening test critical?
Having a family history of a genetic disorder, a previous child with a specific genetic disorder or belonging to a specific ethnic group are predisposing factors, which increase the risk for having a baby with a genetic disorder. In many families, a recessive gene defect can be passed on through generations without ever being known. Thus, if both the partners are carriers for a specific inherited recessive disorder, they would have a 1 in a 4 (25%) chance in each pregnancy, of having a baby with that recessive disease. This screening test helps a couple make informed decisions, based on their carrier status.
Who needs to undergo genetic carrier screening?
- A couple who is considering pregnancy or is already pregnant
- A couple in a consanguineous marriage
- A person with a family history of inherited genetic disorder
- Someone already suffering from an inherited recessive disorder, and planning to have a baby
- A person belonging to a specific ethnic group that has a high carrier rate of a certain genetic disorder
How is it done? (MLPA and NGS)
DNA is extracted from the blood sample of both the partners. It is subjected to Multiplex Ligation-dependent Probe Amplification (MLPA) and Next Generation Sequencing (NGS). MLPA is used to detect deletion and duplication in specific genes, and the NGS panel is used to detect defects in the DNA.
Should both the parents be tested at the same time?
It is recommended that both partners are tested at the same time. A majority of the conditions included in the test panel are autosomal recessive conditions, which require two copies of a defective gene to be inherited. In case both partners are carriers for the same condition, there is an increased risk of having an affected child, which may need further testing. By undergoing the testing process at the same time, the couple will receive risk information in a time-sensitive manner, enabling them to take appropriate, informed decisions.
How can the results of this screening test be interpreted?
A negative result indicates that no significant mutations were detected in the genes tested. This significantly reduces the chances of the couple being carriers of the genes tested. A positive test indicates that a significant mutation was found, which means that the couple is carriers and are at an increased risk to have a child with a genetic disorder. If both the partners are carriers, there is a 25% chance of the baby being unaffected, 25% chance of the baby being affected and 50% chance of the baby being a phenotypically normal heterozygous carrier. In an autosomal recessive disorder, if only one partner is a carrier, there is 50% chance of the baby being unaffected and a 50% chance of the baby being a phenotypically normal heterozygous carrier. Early diagnosis and treatment help prevent life-threatening complications, where possible.
However, there is no test available that can detect all possible mutations that could cause a disorder, leaving behind a small chance (called a residual risk) of being a carrier even after a negative test result. Also, large heterozygous deletions cannot be detected by NGS accurately.
Autosomal Recessive Disorders
If both parents are carriers
- 25% chance of the baby being unaffected
- 25% chance of the baby inheriting a disorder
- 50% chance of the baby being a phenotypically
normal heterozygous carrier
If only one parent is a carrier
If one parent
has a recessive
the other is a
- 50% chance of the baby being a phenotypically
normal heterozygous carrier
- 50% chance of the baby inheriting the
Should the couple go for a screening test every time they plan to have a baby?
Once the couple is tested, the results can be used in all future pregnancies. They do not need to repeat the screening test each time they plan to have a baby.
How much does the Carrier Screening Test cost?
The cost of carrier screening has declined dramatically in recent years due to the advances in technology. As the prices are subject to change, our business development executive will be able to provide all the details.
What are the limitations of the genetic carrier screening test?
- Negative results do not completely exclude the risk/carrier status for the disorders tested (residual risk)
- Since the panel is specific to a set number of genes, and also to the targeted region in these genes (for e.g. coding exons), genetic changes present outside of these targeted regions will not be detected. This is applicable to both NGS and MLPA testing.
- Large heterozygous deletions are not accurately detected by NGS
- It cannot detect the severity of the disorder
- While the results provided have great accuracy, discordance may occur due to bone marrow transplantation, blood transfusions, or other causes, resulting in false negative or false positive results. Additional testing may be necessary to confirm the mutation detected.
Why choose MedGenome Labs for carrier testing?
- Three different test types – Silver, Gold and Platinum Tests, which can chosen based on the couple’s requirement can be chosen
- State-of-the-art technology to provide better data quality and hence, a higher detection rate
- Greater accuracy in reporting and classifying the mutations detected
- Quicker turnaround time – 4 weeks for the Silver and Gold Test, and 6 weeks for the Platinum Test
How will a couple decide which test option is best suited to them?
The Silver Test screens 100 genes and covers the most common recessive disorders in the Indian population. The Gold Test screens a larger number (over 500 genes) and covers both, common as well as rare disorders. The Platinum Test screens over 2000 genes and covers most of the autosomal recessive and X-linked recessive disorders. A physician or a genetic counsellor will be the right person to guide the couple with regard to the right option; taking into consideration the couple’s family history, medical records, background risk and other relevant details.
How can a couple get this test?
The best way for a couple is to discuss it with their doctor. MedGenome Claria also offers free expert genetic counselling by certified genetic counsellors to all couples planning a baby.
They can simply dial 1800-1037590 or SMS “CARRIER” to 56767 and fix an appointment to get a free counselling session.
How long does it take to get the results?
It takes 4 weeks if you take the Silver or Gold Test, and 6 weeks if you take the Platinum Test.
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