Carrier Screening is testing offered to people who do not have any evidence of being affected by a genetic disorder but who may carry an affected gene associated with a disorder. These affected genes could be passed on to a child and have the potential to impact the child’s health.
Some of the genetic disorders we can test for may be something you already have in your family history, but others may cause problems in your baby without any family history.
It is recommended that all pregnant women be screened for Cystic Fibrosis, Spinal Muscular Atrophy (SMA), and Fragile X syndrome once in their lifetime. We now also have expanded carrier screening options for several hundred genetic disorders.
Cystic fibrosis is a genetic (inherited) disease that severely affects breathing and digestion. It is caused by an abnormal gene that makes the body produce thick mucus in the lungs. This mucus promotes infections that are often life-threatening. In the pancreas, similar thick secretions can lead to serious problems with food absorption.
CF carrier testing is a blood test that checks to see if parents-to-be have (carry) the abnormal gene that causes CF. The test can help determine if you’re at increased risk for having a child with CF.
CF is an autosomal recessive condition, which means that the only way to get CF is to have two genes that cause CF—one from your mother and one from your father. This means that both parents must be CF carriers. A CF carrier has only one CF gene and has no CF symptoms. If only one parent is a CF carrier, none of the children will have CF, but there is a 50% chance that each child will be a symptomless carrier. When both parents carry the CF gene, there is a 25% chance (1 in 4) that their child will have CF.
Approximately 1 in 30 Americans is a carrier of the CF gene, but the risk appears to be highest for Caucasian and Ashkenazi Jewish individuals. If you have a family history of CF, you’re more likely to carry the gene than someone from an unaffected family.
Spinal Muscular Atrophy is another autosomal recessive disorder—as described in cystic fibrosis. If affected with SMA, a person may have degeneration of some nerves in the spinal cord. This can lead to muscle weakness and ultimately may even cause death from respiratory failure. The severity of the disease can vary due to different subtypes of the disease. The most common form leads to paralysis and early childhood death, but there are milder forms where a person could live into adulthood with less limitations. Unfortunately, the most common variations tend to be the most serious, and there is no way to predict the severity of disease before it occurs.
About 1 in 35 people are carriers of the SMA gene, and this is the same for all racial and ethnic groups. We can test to see if you are a carrier for this disease. Given the way this condition is inherited, even if your testing is “normal” there is still a very small chance that a child could end up affected with the disease.
Fragile X syndrome is a rare genetic disorder that occurs in approximately 1 out of every 10,000 births. Fragile X syndrome is a genetic condition that causes a range of developmental problems including learning disabilities and cognitive impairment. Usually, males are more severely affected by this disorder than females. Affected individuals usually have delayed development of speech and language by age 2. This disorder is a mutation on the X chromosome.
We now also have expanded carrier screening options (also known as Universal carrier screening or Comprehensive carrier screening) for several hundred genetic disorders. The majority of these disorders are autosomal recessive disorders, which means that the only way for a child to be affected by a specific disease is if both partners are carriers of the same disorder. As carriers, the person would not have any symptoms or evidence of the disease. When both partners carry the gene for the disease, there is a 25% chance (1 in 4) that the child would have this disease. The expanded carrier screening may also detect some X-linked recessive disorders, which means the disease is carried on the X chromosome.