Parents who first learn that they are carriers for a genetic disease because they have a child affected by an autosomal recessive or X-linked recessive condition often fear passing their condition on to another child. Preimplantation genetic testing, or PGT, is an option for parents to reduce their risk for having another child affected by the same disease. PGT, when used as part of in vitro fertilization (IVF), tests embryos for the presence or absence of a genetic condition. Parents can then choose to implant an embryo unaffected by the condition.
Why Undergo PGT?
PGT for parents who already have a child with a genetic condition can be a very different experience compared to couples who learn that they carry a genetic mutation via carrier screening before becoming pregnant.
When each parent is a carrier of a genetic mutation for a specific autosomal recessive disease, like cystic fibrosis or Tay-Sachs disease, their chance of having a child with the disorder — when conceiving without PGT — is 25 percent (the child inherits two copies of the genetic mutation, one copy from each parent). There is a 25 percent chance that their child will inherit two normal copies of the mutation and a 50 percent chance their child will inherit one copy of the mutation, making them an asymptomatic carrier.
Parents typically choose PGT because the experience of having a child with a genetic condition was emotionally, physically, and spiritually traumatic. They wish to avoid going through such trauma again. They may also consider the impact not only on themselves and the potential child, but on their extended family and support system as well.
This was the case for Holly McDonald, whose daughter Cora was born with Tay-Sachs disease, and who chose to continue to build her family with PGT. “We thought of not only what we went through, but what our family and friends went through. We didn’t want to put them through that by having another child with Tay-Sachs. Nor did we want to put another child through it,” says McDonald.
What Are Parents Concerns?
Olive Shihui Zhu, MS, a genetic counselor with Oregon Reproductive Medicine, says that parents of a child with a genetic condition are “more worried than other couples. They want to do more screening tests, want to put all these safety nets in place to prevent it from happening a second time as much as is possible.”
However, she also says a lot depends on how the condition manifests in their family. “We have some families who come in, where the parent has cystic fibrosis, or a relative has it. They may feel it’s a condition that can be treated well medically, that it’s not really detrimental to their own life. So they may feel [PGT] isn’t as necessary in their case.”
Parents can also have different opinions on whether PGT is the right choice for building their family — one partner may not be as eager as the other to pursue this option, so couples may need to have an important discussion.
Age Plays an Important Role
For many parents who have a child with a genetic disorder who choose to do PGT for additional children, time is a major factor. For McDonald, it was important to her and her husband Todd to have their second child as soon as was feasible. McDonald was already over age 40, and they also wanted their second child to know Cora. “There were a lot of mixed feelings,” she says. “But I am very glad that my girls had those eleven months together.”
McDonald also knew that she wanted Tessa, her second child, to have a sibling. “I grew up in a family with lots of siblings, and I knew I wanted to have at least two. Cora’s death definitely played into our wanting to have a third child,” she says. That meant that time, given her age, was an even more pressing factor.
PGT for Parents: What Do Parents Need To Know?
Most important for parents considering PGT to know are the risks and limitations of the IVF/PGT process and their chances of success. It’s also important to understand, says Zhu, that PGT is not available for all genetic conditions. It’s important to start by finding out what type of genetic condition your child has, and consult with healthcare providers like a genetic counselor to see if preimplantation genetic diagnosis with IVF is an option for you.