Spinocerebellar ataxia 27B (SCA27B) is a late-onset (onset after the age of 30 years) and slowly progressive ataxia manifesting with gait imbalance, hand incoordination, and speech disturbance. Half of patients will experience paroxysmal episodes of ataxia of variable duration that may be precipitated by alcohol intake, physical activity, or caffeine. Patients with SCA27B also commonly experience visual disturbances, such as double vision, bouncy vision (oscillopsia), and visual blurring. They may also experience vertigo and dizziness, and tremor of the hands. The disease is slowly progressive and very few people will ever need a wheelchair.
SCA27B is caused by an abnormal expansion of a GAA repeat located in the fibroblast growth factor 14 (FGF14) gene. The diagnosis is established in an individual with compatible symptoms by the identification of this GAA expansion in FGF14. Expansions of more than 300 GAA repeats are generally considered disease-causing, whereas smaller expansions of 250-300 GAA repeats are likely to be disease-causing although may not cause disease in all persons (reduced penetrance).
SCA27B is thought to be a relatively common cause of ataxia in the European population, although it is also found in populations across the world. SCA27B may be as frequent as other common ataxias like SCA3 and SCA6.
SCA27B is inherited in an autosomal dominant manner, which means that each child of an affected parent has a 50% probability of inheriting the disease. However, the of the repeat may vary significantly between generations and, usually, the number of repeats tends to increase when being passed by the mother and decrease when being passed by the father. As a result, the parents of a patient may sometimes be asymptomatic, especially if the expanded copy is inherited from the mother. Conversely, an affected father may pass a smaller copy of the gene that is not disease-causing to his children.
There is no cure for SCA27B. The goals of treatment are to improve quality of life, maximize function, and reduce complications. This ideally involves multidisciplinary care and regular follow up by specialists, such as neurologists, ophthalmologists, physiotherapists, occupational therapists, speech and language therapists, and psychologists. A yearly follow up with a neurologist is recommended.
FGF14