What Is Spinocerebellar Ataxia?
Ataxia is the loss of muscle coordination and can be acquired or genetic: The spinocerebellar ataxias (SCAs) are a group of hereditary ataxias. The SCAs are rare disorders that can involve the cerebellum and other parts of the central nervous system. According to NORD, around 150,000 people in the United States either have or are at risk for hereditary ataxia. Common symptoms of SCAs include gait imbalance, lack of muscle coordination and speech difficulty caused by muscle weakness. SCAs are progressive, which means symptoms get worse over time, and there are currently no disease-modifying treatments available.
How Is Spinocerebellar Ataxia Inherited?
Over 40 SCAs have been identified so far: Each SCA has a distinct genetic cause and characteristic symptoms. The most common SCAs are caused by DNA repeat expansions. In a specific part of a gene, some of the genetic code is repeated more than normal. This could cause a helpful protein to stop working properly, or cause the protein to gain a new, potentially harmful function. These repeat expansions often expand when passed on from parent to child. Larger repeats cause earlier onset and more severe disease. Thus, with many SCAs, the disease can worsen over generations in a family.
All SCAs are inherited in an autosomal dominant pattern: Each child who has a parent with SCA has a 50 percent chance of inheriting that gene change. This is true even if the parent is not yet showing symptoms of SCA, which depends upon the penetrance – the probability of disease presentation.
What Are Reproductive Options With Spinocerebellar Ataxia?
People at risk for an SCA due to family history should seek out a neurologist and a genetic counselor. A neurologist can perform a clinical evaluation for SCAs while a genetic counselor can help patients decide whether and how genetic testing might be right for them. They can provide patients with a risk assessment based on personal and family history, and can explain the implications of a positive result.
Genetic counselors can discuss various reproductive options that are available for someone with SCA that could reduce the chances of having a child with that gene change. These reproductive options include in vitro fertilization (IVF) with preimplantation genetic testing (PGT), IVF with donor eggs, donor sperm or donor embryos, prenatal diagnosis or adoption. Utilization of any of these reproductive options is completely up to the individual. Most people with SCA choose to have children without any effort to prevent the disease from being passed on: There is hope that treatments for SCA will improve greatly by the time any offspring who inherit the gene would express symptoms.
If pursuing IVF with PGT, the embryos would be genetically tested for the SCA gene change before implantation. Embryos that do not carry the gene change would be implanted for a potential pregnancy. While PGT is highly accurate, there is a small risk of an incorrect result. Therefore, prenatal testing can be considered for patients who want to ensure the accuracy of their results and confirm that their fetus does not have SCA prior to delivery, as a follow-up to ensure that the fetus does not have SCA.
For more information on SCA, the National Ataxia Foundation (NAF) and Movement Disorder Society are two excellent resources. NAF has online and in-person support groups and also provides details about signing up for the ataxia patient registry through the Coordination of Rare Diseases at Sanford (CoRDS). There has been no previous SCA research exploring patient knowledge of genetic risk or reproductive options, but a study exploring these questions is currently underway. The study aims to see if those with SCA are interested in options like IVF with PGT while also exploring how personal factors and risk knowledge affect these views.
Suzy Cahn is a second-year Master of Medical Science candidate in Human Genetics and Genetic Counseling at the Genetic Counseling Training Program at Emory University School of Medicine. Her thesis project is investigating Spinocerebellar Ataxia patients’ perceptions regarding reproductive options. She received her Bachelor of Science degree in Biology from St. Mary’s College of Maryland.