Expanded carrier screening is a genetic test designed for individuals and couples planning to have children. It identifies whether a person carries gene variants linked to certain genetic conditions that could be passed on to their offspring. This screening provides information about potential reproductive risks, allowing individuals to make informed decisions about their family planning.
What Expanded Carrier Screening Is
Being a “carrier” for a genetic condition means an individual has one copy of a gene variant that can cause a specific inherited disorder, but does not experience symptoms of the condition themselves. Most conditions identified by expanded carrier screening are inherited in an autosomal recessive manner, meaning a child must inherit two copies of the altered gene, one from each parent, to develop the condition. Some conditions are X-linked, where a female carrier can pass the variant to her children, and males are more commonly affected.
Expanded carrier screening differs from traditional carrier screening by its broader scope. While traditional screening often focuses on a limited number of conditions based on ethnicity or family history, expanded screening tests for a large number of conditions simultaneously, often ranging from 100 to over 600 genes. This “pan-ethnic” approach does not rely on self-reported ancestry, which can be inaccurate or unknown, identifying more couples at risk. This screening provides prospective parents with detailed information about their reproductive risk before or during pregnancy, rather than diagnosing a condition in the individual being tested.
Conditions Screened and The Process
Expanded carrier screening panels encompass a wide range of genetic conditions, including disorders such as cystic fibrosis, spinal muscular atrophy, fragile X syndrome, sickle cell anemia, and Tay-Sachs disease. Panels may also include conditions like Gaucher disease and Canavan disease. The specific conditions included can vary between different testing laboratories, but they focus on disorders that can significantly affect a child’s health and well-being.
The process of undergoing expanded carrier screening is straightforward and non-invasive. It involves providing a small biological sample, which can be either a blood sample or a saliva sample. Once collected, the sample is sent to a specialized laboratory where the DNA is analyzed to identify specific genetic mutations or variants. Ideally, this screening is performed before conception, which allows for more time to consider various reproductive options if an increased risk is identified.
Interpreting and Acting on Results
Understanding the results of expanded carrier screening involves distinguishing between different outcomes. A “negative result” indicates that neither partner was identified as a carrier for the specific conditions included in the screening panel. This suggests a reduced risk of having a child with one of those conditions, though no test is 100% comprehensive and a small residual risk always remains.
A “positive result” means that one or both partners have been identified as carriers for a specific genetic condition. For most autosomal recessive conditions, being a carrier does not affect the individual’s own health, but it means they possess one copy of a gene variant that could be passed to their children. If both partners are identified as carriers for the same autosomal recessive condition, this is considered a “high-risk result,” indicating a 25% chance for each child to inherit two copies of the variant and be affected by the condition. For X-linked conditions, if the female partner is a carrier, there is a 25% chance of having an affected son and a 25% chance of having a carrier daughter with each pregnancy.
Receiving a positive or high-risk result leads to a recommendation for genetic counseling. Genetic counselors are trained professionals who help individuals and couples understand their test results in detail, explain inheritance patterns, and discuss the implications for future pregnancies. They also provide information about various reproductive options available:
- Preimplantation genetic testing (PGT) in conjunction with in vitro fertilization (IVF) to screen embryos before implantation.
- Prenatal diagnosis such as chorionic villus sampling (CVS) or amniocentesis during pregnancy.
- Considering the use of donor sperm or eggs.
- Adoption.
- Preparing for the birth of a child with specific medical needs.