Carrier Screening is a type of genetic testing that can identify whether a person has a gene mutation that may cause a genetic condition. These tests allow people to find out if they are carriers of variants in certain genes that could cause diseases or conditions that are usually recessive. Being a carrier means a person has one copy of the gene variant but does not show signs and symptoms of the condition himself. However, there is a risk to pass it on to offspring.
How does it work?
It involves analyzing a person's DNA through a blood or saliva sample. The DNA sample is tested for specific mutations in certain genes that have been linked to various genetic disorders. Such screening tests are available for hundreds of conditions including cystic fibrosis, spinal muscular atrophy, Tay-Sachs disease, Canavan disease, familial dysautonomia and others. The testing may focus on a panel of several genes associated with common genetic disorders or look at one or a few specific conditions.
Who should consider it?
It is recommended for individuals who are considering becoming pregnant or who are already pregnant. It is also suggested for those with a family history of genetic disorders. Carrier screening before pregnancy allows people to understand their risk and make informed family planning decisions. For example, if both partners are carriers of the same autosomal recessive disorder, they have a 1-in-4 chance with each pregnancy of having an affected child. Such couples may consider preimplantation genetic diagnosis, prenatal diagnosis, use of donor gametes or adoption.
Carrier screening during pregnancy provides reassurance when both partners test negative, while a positive result enables more informed choices via invasive prenatal diagnostic testing. Screening is available for individuals of all ancestries but the risk for certain conditions varies based on ethnic background. For instance, Ashkenazi Jewish individuals have an increased chance of being carriers of Tay-Sachs disease, Canavan disease, cystic fibrosis, familial dysautonomia, Gaucher disease and others.
Panel-based carrier screening tests
A standard screening panel may test for 25-50 common conditions depending on the healthcare provider and laboratory. The American College of Obstetricians and Gynecologists (ACOG) recommends screening all pregnant women for cystic fibrosis, spinal muscular atrophy, and Tay-Sachs diseases regardless of ethnicity. Certain larger expanded screening panels are now available that can screen for over 350 different genetic disorders. While expanded screening detects more carrier couples, it also leads to identifying more variants of unknown clinical significance whose implications are not fully understood. It is best to discuss the benefits and limitations of different screening options with a genetic counselor or physician.
Carrier screening results and interpretation
Carrier screening results are typically reported as positive, negative or variant of unknown significance. A positive result means a person has been identified as a carrier of a mutation that can cause disease. Carrier status alone does not indicate an increased risk for health issues. A negative result indicates no known pathogenic variants were detected for the conditions tested. In some cases, a variant of unknown significance may be identified, meaning there is an unknown clinical effect and the status remains unclear until more information emerges. Follow-up genetic counseling helps understand results and family planning implications. Screening should focus on conditions that are medically actionable based on knowledge of prevention or management options to reduce anxiety.
Importance of informed decision making
While carrier screening provides helpful information, it is not without limitations. No test is 100% sensitive and a negative result does not guarantee both partners are non-carriers. There also remains the possibility of variants that have not been identified yet. Patients and healthcare providers should have informed discussions on benefits and limitations to ensure screening aligns with individual values, lifestyle and family history. Open communication and support are necessary to make the screening process meaningful and avoid potential adverse psychological impact of unclear or unexpected results. Overall, when used appropriately with pre- and post-test counseling, it is an important reproductive health tool.
Carrier screening - what it tests for, how it works, who should consider it and important aspects of result interpretation and informed consent. The various types and panels of screening tests available were discussed along with emphasizing the role of genetic counselling in the decision making process.
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