Will I Pass ARSACS to My Children? Inheritance Explained

If you have Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS), it is very unlikely that your children will develop the condition unless your partner is also a carrier of a disease-causing variant in the SACS gene. Because ARSACS is a rare disease globally, the odds of a non-related partner being a carrier are extremely low.

How ARSACS Inheritance Works

ARSACS is an autosomal recessive condition, which means it is caused by non-working variants in the SACS gene ^[1]. We all have two copies of the SACS gene—one inherited from each parent. To develop ARSACS, a person must inherit a non-working copy from both parents.

Because you have ARSACS, you have two non-working copies of the SACS gene. You will pass one of these copies to every child you have. As a result, all of your children will automatically be genetic carriers. A carrier is someone who has one non-working gene and one working gene. They typically do not experience symptoms of the disease.

For your child to actually have ARSACS, your partner must also pass down a non-working SACS gene.

• If your partner is not a carrier: There is virtually no chance your children will have ARSACS ^[1]. All of your children will be healthy carriers. (Note: While your children will not have your mobility or coordination issues, they will eventually need to be informed of their carrier status when they grow up and plan their own families.)
• If your partner is a carrier: There is a 50% chance with each pregnancy that your child will inherit the variant from both of you and develop ARSACS. There is also a 50% chance they will just be a carrier.

Risk Based on Where You Live

The likelihood of your partner being a carrier depends heavily on their geographic and ancestral background. While ARSACS is now recognized as one of the more common recessive ataxias worldwide ^[2], the overall chance of a random person in the general global population being a carrier remains very small.

However, the risk is much higher for individuals with French-Canadian ancestry, specifically those with roots in the Charlevoix and Saguenay–Lac-Saint-Jean regions of Quebec. In these specific areas, the carrier frequency is estimated to be about 1 in every 22 people ^[3]. If your partner has ancestors from these regions, their chance of being a carrier is significantly elevated.

Next Steps: Genetic Counseling and Testing

Navigating family planning with a progressive condition carries emotional weight. Because the risk to your future children depends entirely on your partner’s genetics, the most important step for family planning is for your partner to be evaluated ^[3]. It is highly recommended to explore these options before pregnancy (preconception) to maximize your family planning choices.

• Genetic Counseling: Ask your neurologist for a referral to a genetic counselor. They can review both of your family histories, explain your specific risks in detail, and help you navigate your options with compassion for the emotional complexities of family planning.
• Carrier Screening: Your partner can undergo a genetic test (usually a simple blood or saliva test) to see if they carry a variant in the SACS gene ^[3]. Important: Your partner’s doctor must know that you have ARSACS so they can order comprehensive sequencing of the SACS gene. Standard prenatal carrier screening panels often exclude rare diseases or only test for the specific Quebec variant, which could lead to a falsely reassuring negative result if your partner has a different variant.

If your partner is found to be a carrier, a genetic counselor can help you explore family planning options, such as preimplantation genetic testing (where embryos are screened during in vitro fertilization before being implanted) or prenatal testing during a pregnancy.