A disease-causing allele is a variation in a gene’s DNA sequence that can lead to a health condition. Everyone inherits two copies of each gene, one from each parent. While many allele variations are harmless, a disease-causing allele can disrupt normal biological processes, potentially resulting in a health disorder.
Knowing if a fetus or newborn carries such an allele allows for early understanding and preparation. This knowledge enables timely interventions, treatments, or specialized care, which can improve outcomes. It also empowers parents to make informed decisions and access support.
Screening Before and During Pregnancy
Several methods are available to assess disease-causing alleles before and during pregnancy. These tests offer insights at different stages, from preconception to later trimesters, providing valuable information for parents.
Carrier Screening
Carrier screening is genetic testing performed on prospective parents, ideally before conception or in early pregnancy. This blood or saliva test determines if an individual carries a pathogenic variant in a gene that could cause a specific health condition. Individuals who are carriers typically do not exhibit symptoms themselves because they possess one functional copy of the gene, but they can pass the non-working copy to their biological children. If both parents are carriers for the same recessive condition, there is a 25% chance with each pregnancy that their child will inherit two copies of the altered gene and develop the condition. Common examples include cystic fibrosis, spinal muscular atrophy, and fragile X syndrome.
Non-Invasive Prenatal Testing (NIPT)
Non-Invasive Prenatal Testing (NIPT) is a blood test performed on the pregnant parent, typically starting at 10 weeks of gestation. This screening analyzes small fragments of fetal DNA that circulate in the pregnant person’s bloodstream, which originate from the placenta. NIPT primarily screens for common chromosomal conditions, such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13), and can also determine the sex of the fetus. It is non-invasive, requiring only a blood draw from the pregnant parent and posing no physical risk to the fetus. NIPT is a screening test, not a diagnostic one, meaning it estimates risk rather than providing a definitive diagnosis.
Chorionic Villus Sampling (CVS)
Chorionic Villus Sampling (CVS) is an invasive diagnostic procedure typically performed between 10 and 13 weeks of pregnancy. This test involves obtaining a small tissue sample from the chorionic villi, tiny projections of placental tissue that share the same genetic material as the fetus. The sample is collected either transabdominally (through the abdomen with a needle) or transcervically (through the cervix with a thin tube or forceps), guided by ultrasound. CVS is used to diagnose chromosomal abnormalities and specific single-gene disorders, offering high diagnostic accuracy.
Amniocentesis
Amniocentesis is another invasive diagnostic procedure, usually performed in the second trimester, specifically between 15 and 20 weeks of pregnancy. During this procedure, a thin, hollow needle is inserted through the pregnant person’s abdomen and uterus, guided by ultrasound, to withdraw a small amount of amniotic fluid. This fluid contains fetal cells that can be analyzed for chromosomal abnormalities, genetic conditions like Down syndrome or spina bifida, and certain metabolic disorders. While highly accurate, both CVS and amniocentesis carry a small risk of complications, including miscarriage.
Screening After Birth
Newborn screening detects serious, treatable conditions early, often before symptoms appear. This allows for timely intervention, which can improve health outcomes and prevent severe disability or death.
The procedure for newborn screening involves a “heel prick” blood test. A healthcare professional gently pricks the baby’s heel, usually between 24 and 72 hours after birth, to collect a few drops of blood onto a filter paper card. This card is then sent to a laboratory for analysis. The heel prick may cause brief discomfort to the baby, but measures like warming the heel or feeding during the procedure can help minimize this.
Conditions screened for vary by region, but generally include metabolic disorders (e.g., phenylketonuria, galactosemia), endocrine disorders (e.g., congenital hypothyroidism), and certain genetic conditions (e.g., cystic fibrosis, sickle cell disease). Some states screen for over 50 different disorders.
Understanding Test Results and Genetic Counseling
Once genetic tests are performed, understanding the results is a subsequent step for parents. Screening tests, like NIPT or newborn screening, provide a risk assessment or indicate a potential issue. A “positive screen” means an increased likelihood of a condition, but it does not confirm a diagnosis. Diagnostic tests, such as CVS or amniocentesis, offer a definitive answer regarding the presence of a specific genetic condition.
If a screening test indicates a potential issue, confirmatory testing with a diagnostic procedure is often recommended to verify the results. Genetic laboratories classify identified genetic changes as benign, pathogenic (disease-causing), or variants of uncertain significance (VUS). A pathogenic result suggests the likely cause of a condition, while a VUS means there is not enough evidence to determine its impact.
Genetic counselors play an important role in guiding families through this process. These professionals are trained to explain complex genetic information, test results, and inheritance patterns in an understandable manner. They discuss the implications of the results for the child’s health and the family, providing non-directive support and exploring various options. Genetic counselors also help assess the likelihood of genetic conditions based on family history and medical background.
Receiving genetic information can have a significant emotional impact. Genetic counselors offer a safe space for parents to express feelings, provide emotional support, and help families navigate challenges. They discuss next steps and connect families with resources and support networks.