Spinocerebellar Ataxia Type 3

Clinical characteristics: Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease (MJD), is characterized by progressive cerebellar ataxia and variable findings including pyramidal signs, a dystonic-rigid extrapyramidal syndrome, significant peripheral amyotrophy and generalized areflexia, progressive external ophthalmoplegia, action-induced facial and lingual fasciculations, and bulging eyes. Neurologic findings tend to evolve as the disorder progresses.

Diagnosis/testing: The diagnosis of SCA3 is established in a proband with suggestive findings and a heterozygous abnormal CAG trinucleotide repeat expansion in ATXN3 identified by molecular genetic testing.

Management: Treatment of manifestations: Management is supportive as no medication slows the course of disease. The goals of treatment are to maximize function and reduce complications. It is recommended that each individual be managed by a multidisciplinary team of relevant specialists such as neurologists, occupational therapists, physical therapists, physiatrists, orthopedists, nutritionists, speech therapists, social workers, and psychologists. Various manifestations may respond to pharmacologic agents. Regular physical activity is recommended, including combined physical and occupational therapy focused on gait and coordination. Canes and walkers help prevent falling; motorized scooters, weighted eating utensils, and dressing hooks help to maintain independence. Speech therapy and communication devices may benefit those with dysarthria, and dietary modification those with dysphagia. Other recommendations include home adaptations to prevent falls and improve mobility, dietary supplements if caloric intake is reduced, weight control to facilitate ambulation and mobility, and caution with general anesthesia. Surveillance: Annual assessments (or more frequently as needed) of neurologic findings (e.g., dysarthria, dysphagia, bladder dysfunction, neuropathic pain, cognitive and psychiatric manifestations), weight and nutritional status, and social support.

Genetic counseling: SCA3 is inherited in an autosomal dominant manner. Each child of an affected individual has a 50% chance of inheriting the ATXN3 CAG repeat expansion. Once the CAG repeat expansion has been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic testing are possible. Note: The prenatal finding of an ATXN3 CAG repeat expansion cannot be used to accurately predict onset, severity, type of symptoms, or rate of progression of SCA3.