Carrier Screening

Carrier screening is a type of genetic testing performed on individuals who do not show symptoms of a genetic disorder but may be carriers of a recessive (or X linked) genetic mutation. This screening is important for understanding the risk of having a child with a genetic disorder, especially when there is a family history or when belonging to certain ethnic groups that are known to have a higher risk for specific genetic conditions.

RANZCOG says that information on carrier screening should be given to all women planning pregnancy or in the first trimester.

Carrier Screening Tests

  • 3 Gene Panel
    • Funding for 3 gene reproductive carrier screening was included in the MBS on 1st November 2023.
    • The three-gene panel looks for mutations causing three common genetic conditions:
      • Cystic fibrosis (CF)
      • Spinal muscular atrophy (SMA)
      • Fragile X syndrome
    • Around 5% of people in Australia will carry a mutation for one of these conditions.
    • Usually the woman is tested first.
    • One in 240 couples will both be carriers and these couples are at risk of having an affected child.
  • Expanded Panel
    • An expanded reproductive carrier screen (Beacon) looks for mutations that can cause over 400 recessive conditions.
    • Because so many genes are screened, about 50-75% of people in Australia will be carriers for one or more of these conditions so it is recommended that both partners be tested simultaneously.
    • One in 44 couples will both be carriers of the same condition and at risk of having an affected child.
  • Type of disorders that can be screened for
    • Cystic Fibrosis (CF): Common in Caucasian populations.
    • Spinal Muscular Atrophy (SMA): A genetic disorder affecting muscle control, not specific to any ethnic group.
    • Sickle Cell Disease: Prevalent in African and Mediterranean populations.
    • Thalassemias: Common in Mediterranean, Southeast Asian, and African populations.
    • Tay-Sachs Disease: Often found in Ashkenazi Jewish, Cajun, and French-Canadian populations.
    • BRCA1 & BRCA2: Often found in Ashkenazi Jewish, Icelandic, Norwegian

Ethical and Social Considerations:

  • Informed Consent: Individuals should provide informed consent, understanding the purpose, potential outcomes, and implications of the screening.
  • Privacy and Confidentiality: The privacy of genetic information must be protected.
  • Cultural Sensitivity: Sensitivity to how different cultures view genetic screening and genetic disorders is crucial.
  • Genetic Counseling: Genetic counseling is important to help understand the results and make informed decisions. Regardless of the chosen path, genetic counseling is highly recommended. A genetic counselor can provide detailed information, discuss the likelihood of the disorder being passed on, and help the couple understand their options.
  • Emotional Support and Considerations: It’s important to consider the emotional and psychological impact of these decisions. Couples may benefit from support groups or counseling to navigate these choices.

Options where both parents are carriers

When both parents are carriers of the same genetic disorder, there is a risk of passing that disorder on to their offspring. The specific risk varies depending on the disorder and the mode of inheritance, but for autosomal recessive conditions, there is a 25% chance with each pregnancy that the child will inherit both copies of the defective gene and be affected by the disorder. In this scenario, there are several options available to the couple:

  1. Natural Conception with Prenatal Testing: Couples may choose to conceive naturally and utilize prenatal testing to determine if the fetus is affected. Options for prenatal testing include:
    1. Chorionic Villus Sampling (CVS): Performed typically between the 10th and 13th weeks of pregnancy.
    2. Amniocentesis: Usually done between the 15th and 20th weeks. Both procedures carry a small risk of miscarriage and are used to obtain cells from the fetus to test for the genetic disorder.
  2. Preimplantation Genetic Diagnosis (PGD): This option is used in conjunction with in vitro fertilization (IVF). Embryos created through IVF are tested for the genetic disorder, and only unaffected embryos are implanted in the uterus. 
  3. Use of Donor Sperm or Eggs: Couples may opt to use sperm or eggs from a donor who is not a carrier of the genetic disorder. 
  4. Adoption: Some couples may choose to adopt a child instead of having a biological child.
  5. Childfree Living: Some may opt not to have children, either focusing on other aspects of their life or possibly providing care to others in different capacities.

Each option comes with its own set of ethical, emotional, and financial considerations. The choice depends on individual preferences, values, risk tolerance, and the specific details of the genetic disorder in question. The decision-making process is often complex and highly personal, requiring thorough understanding and thoughtful consideration.