Carrier screening helps a couple understand their risk and probability of passing on inherited genetic disorders, such as sickle-cell anemia, spinal muscular atrophy, to their children.
We carry two copies of our genes in our DNA; one copy from each parent. A gene has two versions, a dominant and a recessive version (allele). Dominant alleles express themselves even if an individual only has one copy of that allele. Recessive alleles express themselves only when an individual has both copies of that allele. Certain disorders are recessive genetic disorders caused by the presence of two recessive alleles, such as cystic fibrosis and spinal muscular atrophy. When two healthy parents are both carriers of a causative recessive allele, there is a 25% probability that they will both pass their recessive alleles to their child with a devastating outcome.
Various genetic tests are available to test intended parents to help determine their carrier status for known inherited genetic disorders and the probability of passing on causative recessive alleles to their children.
Types of carrier screening genetic tests
Carrier screening tests are performed using blood, saliva, or a cheek swab collected from a couple. Tests are available that employ biochemical enzyme screening or molecular genetic screening. With advances in molecular genetic screening, it has become the preferred method since enzyme screening might miss some carriers.
Traditional molecular genetic screening tests are targeted carrier screening tests that focus on analyzing one or several causative genetic changes and are recommended based on your family history or ethnicity.
Expanded carrier screening is now recommended for all ethnicities due to the prevalence of mixed populations, causing difficulties in determining who is at risk based on ethnicity.
Expanded carrier screening covers many more genetic disorders in one test using one sample. Available tests have different coverage in terms of number of genes and ethnicities included. Depending on the test ordered, it can cover from tens to hundreds of genes across a broad range of ethnicities.
New genetic analysis technologies, such as microarrays and next-generation sequencing, are enabling comprehensive, efficient, and cost-effective expanded carrier screening tests for the analysis of more causative genetic variants across a broad range of ethnicities. Microarrays, a technology that can analyze DNA of known genes from the entire human genome in one test, can screen all known causative variants for inherited diseases by consolidating multiple targeted tests on multiple technology platforms into one test, resulting in a quick, comprehensive reporting of a couple’s carrier status.
Benefits of carrier screening
Having genetic information by carrier screening enables intended parents to determine their risk and probability of passing on an inherited genetic disorder to their children. It is especially crucial to couples with family history and those from certain ethnicities, such as Tay-Sachs disease occurring at a higher rate in Ashkenazi Jews or thalassemia in South East Asians. Preconception carrier screening is most beneficial to a couple working with their genetic counselor to make informed decisions and provides the opportunity to explore options before becoming pregnant.