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If you’re thinking about starting or expanding your family, you may wonder if you or your partner have a heritable genetic disease. And, if so, how can you prevent your offspring from inheriting a disabling condition? Genetic carrier screening is the first step in understanding any genetic risk you may carry, particularly if you and your partner don’t have or show symptoms of any inherited condition.

What Does it Mean To Be a Carrier?

You inherit two copies of every gene, one from your biological mother and one from your biological father. To develop a recessive genetic condition, you must inherit two copies of a mutated gene. If you inherit only one copy of the mutation, you are a carrier of the condition. Being a carrier doesn’t necessarily mean you will pass along a disease to your child. It takes two carrier-parents to create an increased risk. You may carry a recessive mutation for a disorder but have no history of anyone in your family having the condition. That’s where carrier screening comes in.

What Is Genetic Carrier Screening?

You have a choice of two types of carrier screening: targeted or expanded screening.

A targeted carrier screening looks for diseases common in people of your ethnicity. An expanded carrier screening takes a broader look at many more diseases and doesn’t limit by ethnicity. The expanded carrier screening screens for mutations related to more than 100 conditions. The American College of Obstetrics and Gynecology (ACOG), a professional society that provides guidance to physicians, suggests that both carrier screening by ethnicity and expanded screening are appropriate for couples planning to become pregnant.

The American College of Medical Genetics and Genomics (ACMG), which provides guidance for medical geneticists, suggests that expanded screening is appropriate for most people, but still recommends a more tailored approach by choosing to screen only for conditions most relevant to the couple. Ultimately, it’s between you and your doctor whether you want to limit your screening by ethnicity or certain conditions, or if you want to have an expanded screening.

How Does Carrier Screening Work?

Carrier screenings generally look for conditions that can be treated with early intervention, lead to a shorter life expectancy, cause disability or have no treatment options. These conditions include:

  • Cystic fibrosis
  • Tay-Sachs disease
  • Spinal muscular atrophy
  • Wilson disease
  • Galactosemia
  • Fragile X syndrome
  • Krabbe disease
  • Bloom syndrome
  • Thalassemia

Some healthcare providers screen both parents-to-be at the same time so that the report will provide specific risk numbers for each disease included on the panel for both you and your partner. Other healthcare providers will do screening sequentially, meaning the male partner is only screened if the female is found to be a carrier. If your partner is also a carrier for the same disease, it’s time to speak to a genetic counselor. Many of these conditions are rare to begin with, and for both partners to be carriers is even rarer.

What Happens If Both Partners Are Carriers?

A genetic counselor is essential to understanding your results and what next steps are available to you. If, for example, you’re both carriers for cystic fibrosis, each of your children has a 25 percent (1 in 4) chance of developing cystic fibrosis and a 25 percent chance of being completely free of the mutation. Each child has a 50 percent chance (1 in 2) of being a carrier of the recessive mutation.

What happens next is up to you, your partner and your doctor. What you choose to do may depend on the condition and available treatment options.

You may be comfortable moving forward with starting your family without taking any steps to reduce the chance of having a child affected with the condition. This may be because you feel the condition is mild, treatable, or because the options for preventing the transmission of the disease are not acceptable to you.

There is also prenatal diagnosis through amniocentesis or chorionic villus sampling. You can choose to use donor eggs or sperm that have screened negative for the condition to reduce the risk of passing it on. You may also consider preimplantation genetic testing (PGT). PGT is done in conjunction with in vitro fertilization. Embryos are tested for the mutation, and those free of the mutation are available to be implanted with the hope of becoming pregnant.

Consider What Is Best for You

Each option is a big decision and something to carefully consider with your doctor. No test is perfect, and although carrier screening has a high accuracy rate, false negatives (when the test comes back negative, but you do carry the mutation) and false positives (when the test comes back positive, but you are not a carrier) are possible. Talk through the risks and benefits of each option with your doctor and genetic counselor to ensure you’re making the best decision for your growing family.