What Is the Chance of Passing ADCA to Children?

If you have been diagnosed with an autosomal dominant cerebellar ataxia (ADCA), there is exactly a 50% chance of passing the genetic mutation to each of your children ^[1]. This risk remains the same for every pregnancy, regardless of the child’s sex or whether their siblings have inherited the condition.

Learning that you could pass a neurodegenerative condition to your children can cause immense anxiety and parental guilt. These feelings are completely normal. The information below is designed to help you understand the genetics, empowering you and your family to make informed decisions about testing and family planning.

What Does “Autosomal Dominant” Mean?

The term autosomal means the mutated gene is located on a non-sex chromosome, meaning it affects men and women equally. The term dominant means that inheriting just one copy of the mutated gene from one parent is enough to cause the condition ^[1].

Because it is a dominant condition, ADCA generally does not “skip” generations. Most importantly: if a child does not inherit the mutated gene, they will not develop the condition, and they cannot pass it on to their future children.

Why It Can Sometimes Look Like It “Skips” a Generation

Even though the inheritance risk is a strict 50%, the condition can sometimes appear to skip a generation within a family tree. This happens for a few key medical reasons:

• Variable Penetrance and Expressivity: Some individuals who inherit the gene mutation may never develop noticeable symptoms; this is known as reduced penetrance ^[2][3]. Others might develop symptoms, but they may be very mild or feature different symptoms than their parent, which is known as variable expressivity ^[4][5]. Both scenarios can make it appear as though the condition skipped a person.
• Age of Onset: ADCA often does not cause symptoms until middle or later adulthood. The age when symptoms start can vary widely even within the same family. A parent might carry the gene but pass away from unrelated causes before they ever develop ataxia symptoms ^[3].
• Anticipation: In many subtypes of ADCA (especially the spinocerebellar ataxias, or SCAs), the underlying genetic mutation can expand or grow larger when it is passed down to the next generation ^[6]. This can cause the disease to appear at an earlier age and with more severe symptoms in the child than it did in the parent.

Family Planning and Reproductive Options

If you are planning to have children and know you have an ADCA mutation, you do not simply have to “roll the dice.” A genetic counselor can help you explore reproductive options, such as Preimplantation Genetic Testing (PGT). This involves using in vitro fertilization (IVF) to screen embryos for the genetic mutation, allowing you to ensure the condition is not passed to future generations ^[7][8].

Predictive Testing and Genetic Counseling

Because ADCA often develops later in life, your children may reach adulthood before knowing if they have inherited the condition. Many adults who are at risk consider predictive genetic testing—a test to determine if they carry the mutation before any symptoms appear.

It is a common first instinct for a parent to want to test their young children immediately to prepare for the future. However, international medical guidelines strongly emphasize that predictive testing for adult-onset, non-curable conditions should only be performed on adults who voluntarily request it ^[9][10]. This rule exists to protect the child’s right to decide for themselves whether they want this heavy, life-altering information when they are mature enough to fully understand it ^[11].

Testing is a deeply personal and complex decision, and it must be accompanied by comprehensive genetic counseling ^[9]. A genetic counselor will help your children or extended family members (such as siblings, who are also at a 50% risk) understand the medical, emotional, and practical implications of testing, like the potential impacts on life insurance ^[7][8]. This multi-step counseling process helps families navigate the psychological weight of their results, establish a support system, and figure out the best ways to communicate this diagnosis with other relatives ^[12][13].