Most babies are born healthy, but with every pregnancy, there is a risk that a child with a genetic disorder will be born. Heterozygote carrier screening tests can tell you your chance of passing the genetic disease to your offspring. This type of genetic test analyses your DNA to reveal if you are a carrier of one or more genetic disorders. Carriers have changes in a specific gene or genes, which increases their risk of having a child with a genetic disease or a congenital defect. The test allows a more precise assessment of the risk for your offspring to have certain genetic disorders. This information will enable you to make an informed decision about your reproductive plans. The screening tests typically use venous blood or buccal samples, from which genome DNA is isolated and then analysed by next-generation sequencing (NGS). The genetic analysis itself looks to find DNA changes called variants. Results take about four weeks.
If you are a carrier, you have a change (called genetic variant) in one of the copies of a given gene, which increases the risk of having a child affected by the related genetic disorder. For most of the disorders included in the screening panel, both reproductive partners have to be carriers (of the same disorder) for their offspring to be affected. However, some genetic diseases are linked to the X-chromosome, which means that they are usually passed on by carrier mothers and affect boys more often. It is important to know that:
- Everyone is a carrier of one or more genetic disorders;
- Carriers are typically healthy and have no symptoms;
- Carriers usually have no family history of a hereditary disease;
- For children of families with a confirmed high risk of a genetic disorder, genetic counselling is recommended to discuss options for prophylaxis of congenital disease.
Heterozygous carrier screening can offer valuable information to people who:
- Are pregnant at the moment or are planning pregnancy;
- Have a higher risk of a specific disease because of their ethnicity;
- Have a family history of a genetic disorder;
- Plan to donate eggs or sperm;
- Would like to know more about the risk of having a child with a genetic disorder.
Types of heterozygous carrier screening panels
The heterozygous screening test is offered in three basic variants:
- Basic panel (3 genes);
- Additional panel (46 genes);
- Extended panel (288 genes).
Includes screening for variants of the CFTR-gene, causing cystic fibrosis (CF), the FMR1-gene for the Fragile-X syndrome and the SMN1-gene for spinal muscular atrophy (SMA). This panel is suitable for patients who want to know the risk of their offspring being affected by some of the most frequent genetic disorders.
Cystic fibrosis is characterised by progressive damage to the respiratory and digestive systems. With adequate treatment, the life expectancy of patients with severe CF can reach up to 30 years (sometimes even more). One in every 25-30 Caucasians are carriers for CF.
Spinal muscular atrophy is characterised by severe muscle weakness and progressive loss of muscle control. In severe forms of SMA, the lethal outcome can occur before the age of two. One in 33 Bulgarians is a carrier for SMA.
Fragile-X syndrome is the most common cause of congenital cognitive impairment. Life expectancy is usually normal. One in 178 women is a carrier for the condition.
ADDITIONAL PANEL (up to 46 genes)
This panel is suitable for patients who wish to be screened for a broader spectrum of severe genetic disorders. The test panel includes all genetic disorders recommended by the American College of Obstetrics and Gynecology (ACOG) and the American College of Medical Genetics (ACMG), as well as genetic disorders with high prevalence in certain ethnic groups; abnormalities that can manifest in severe clinical symptoms with a strong negative impact on the quality of life; some Х-linked disorders, including the fragile-X syndrome and Duchenne and Becker muscular dystrophy.
EXTENDED PANEL (up to 288 genes)
This panel is suitable for patients of all ethnic groups, who wish to have a more comprehensive carrier screening. The panel includes all genetic disorders, recommended by the American College of Obstetrics and Gynecology (ACOG) and the American College of Medical Genetics (ACMG), as well as genetic disorders with high prevalence in certain ethnic groups; abnormalities that can manifest in severe clinical symptoms with a strong negative impact on the quality of life; some Х-linked disorders, including the fragile-X syndrome.
A positive result
This means that a pathogenic variant was detected, and you are a carrier for one or more of the genetic disorders in the panel. Being a carrier does not usually pose risks for your own health, but it increases the risk of having a child affected by the genetic disorder in question. The next step typically is to screen your reproductive partner. In such cases, medical counselling is recommended.
A negative result
This means that no pathogenic variants were identified for any of the genetic disorders tested. A negative result gives peace of mind since the risk of having a child affected by any of the genetic conditions in the panel is significantly reduced. However, no single test can identify all carriers, so there remains a slight chance, called residual risk, that you are a carrier.