.png){kind=small}
With the arrival of the Lunar Year of the Dragon, many expectant parents hope to have a ‘Dragon Baby’ this year. When searching for information online, they often come across ‘Recessive Carrier Testing’ and ‘Non-Invasive Prenatal Testing (NIPT)’. What are the differences between the two? Do you need to choose one or do both? Let’s discuss the differences between them this time!
What is recessive carrier testing?
Individuals or couples at risk of having a child with an autosomal recessive or X-linked genetic disorder can be identify using recessive carrier testing [1]。Therefore, most recessive genetic disorder carrier tests are conducted before pregnancy.
Each person has 22 sets of autosomes and one pair of sex chromosomes. For autosomal recessive traits to manifest, offspring must receive recessive alleles from both parents. When it comes to X-linked genetic disorders, things get more complex. If a woman is a carrier of X-linked genetic disorders, her male offspring has a 50% chance of inheriting the disorder as they receive only one X chromosome, and her female offspring has a 50% chance of becoming carriers of the disorder as they receive two X chromosomes.
By performing recessive carrier testing, individuals or couples can see whether they are autosomal recessive diseases or X-linked genetic disorder carrier. This information can help them make decisions about starting a family and consider options such as not having a baby or undergoing IVF (in vitro fertilization) to have a healthy baby if necessary.
However, there remain ethical considerations regarding the use of specifically chosen healthy germ cells for IVF, as it essentially involves engineering babies at a different level, and there is much that needs to be debated in this area.
What is Non-Invasive Prenatal Testing (NIPT)？
NIPT stands for Non-invasive Prenatal Screening Test and is one of the most widely used techniques for analyzing and detecting fetal chromosomal abnormalities (see table 1) or identifying fetus’s sex in the early stage of pregnancy[3]。Therefore, non-invasive prenatal testing is only conducted during pregnancy.
Table 1: Common Chromosomal Abnormalities Detectable by NIPT
Down syndrome (trisomy 21) |
Edwards syndrome (trisomy 18) |
Patau syndrome (trisomy 13) |
Turner syndrome and Klinefelter syndrome (extra or missing copies of X or Y chromosome) |
However, the specific tests available may vary by provider. Please consult with your obstetrician to find the most suitable testing plan for you.
How does NIPT work?
A small quantity of blood is taken from a pregnant mother who is at least 10 weeks along, and this blood contains fragments of the fetus' DNA [2]. Through the use of next-generation sequencing (NGS), the analysis of these fragments can reveal genetic variations that indicate chromosomal abnormalities, providing the mother with information about the baby's health before birth and allowing her to make decisions if the results are positive [4].
Some of the abnormalities may not be fatal, thus enabling mothers to begin treatment for their children as soon as possible. It should be noted that NIPT is only a screening test and can only inform the risk of having abnormal conditions. Diagnostic tests like amniocentesis and chorionic villus sampling can be performed for exact results [1].
What are the limitations of NIPT and Recessive Carrier Test?
Both tests have some detection limitations.
NIPT can only detect specific aneuploidies and require a confirmatory test for all positive NIPT results. The test is not accessible for pregnancies with triplets or higher, for pregnant women who have features that may interfere with testing, and for women who have undergone an organ transplant or received a recent blood transfusion [4].
In recessive carrier tests, a negative screening report does not necessarily rule out carrier status because it only indicates the presence of a well-established variant at the time of testing. Additionally, positive screening results may not accurately predict the phenotype of affected individuals because some disorders are linked to incomplete penetrance and intra-familial variability [6].
Difference between Recessive Carrier Test and NIPT?
The recessive carrier test and NIPT differ primarily in their suitability for testing at different stages: the former is usually done prior to pregnancy, whereas the latter is carried out post-pregnancy.
Due to the ability of recessive carrier test to determine the baby's condition before conception, it become more and more popular, particularly among individuals who have religious objections to abortion or suspect that they may be carriers of recessive traits.
The CoGenesis® Family carrier screening test includes 587 genes related to more common pan-ethnic recessive genetic diseases, such as alpha thalassemia, congenital deafness, spinal muscular atrophy, and various severe syndromes, which are the most common among Chinese. It also includes 80+ treatable congenital metabolic defects that can benefit from early pregnancy and newborn planning.
If you and your partner are preparing to have a baby or have any questions about your situation, you should consult an obstetrician for an evaluation as soon as possible.
References:
Gregg, A.R., Aarabi, M., Klugman, S., Leach, N.T., Bashford, M.T., Goldwaser, T., Chen, E., Sparks, T.N., Reddi, H.V., Rajkovic, A. and Dungan, J.S. (2021). Screening for autosomal recessive and X-linked conditions during pregnancy and preconception: a practice resource of the American College of Medical Genetics and Genomics (ACMG). Genetics in Medicine, 23(10), pp.1793–1806.
Cleveland Clinic (2022). NIPT Test (Noninvasive Prenatal Testing): What To Expect. [online] Cleveland Clinic.
Medline Plus (2021). What is noninvasive prenatal testing (NIPT) and what disorders can it screen for?: MedlinePlus Genetics. [online] medlineplus.gov.
Non-invasive prenatal testing (NIPT) — Knowledge Hub. (n.d.). GeNotes. https://www.genomicseducation.hee.nhs.uk/genotes/knowledge-hub/non-invasive-prenatal-testing-nipt/
Siva Shantini Jayashankar, Muhammad Luqman Nasaruddin, Muhammad Faiz Hassan, Rima Anggrena Dasrilsyah, Mohamad Nasir Shafiee, Noor and Alias, E. (2023). Non-Invasive Prenatal Testing (NIPT): Reliability, Challenges, and Future Directions. Diagnostics, 13(15), pp.2570–2570.
View of Expanded carrier screening for recessive genetic disorders: a review. (2024).
Comments