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Spinocerebellar ataxia type 3 (SCA3), also called Machado-Joseph disease, is a progressive neurologic condition caused by a CAG repeat expansion in ATXN3. It is inherited in an autosomal dominant pattern, but age at onset, symptoms, and rate of change vary widely, including within a family. The historical numbered “types” do not define a person's future course. GeneReviews provides condition-specific diagnosis and management guidance.
Urgent and procedure-related safety
Sudden one-sided weakness, facial droop, a severe new headache, acute confusion, collapse, or an abrupt major change in balance or speech needs emergency assessment; progression of SCA3 is generally gradual, and stroke, infection, medication effects, injury, or another illness may be responsible.
Seek urgent help for breathing difficulty, repeated choking with difficulty recovering, inability to swallow liquids or manage secretions, signs of dehydration, a serious fall or head injury, or a marked reduction in alertness. Fever, wet breathing or voice, and new chest symptoms after eating or drinking may signal aspiration-related illness.
Before surgery or sedation, the team should know about dysphagia, respiratory symptoms, sleep apnea, dystonia or spasticity, current mobility and positioning, medicines, and communication access. Medication changes and treatment of pain, sleep, spasticity, dystonia, or mood should account for fall risk, alertness, and swallowing.
Quick reference
| Topic | Condition-specific guidance |
|---|---|
| Current name | Spinocerebellar ataxia type 3; Machado-Joseph disease remains a recognized synonym |
| Cause | Heterozygous CAG repeat expansion in ATXN3 |
| Diagnosis | Neurologic phenotype, family history, and a test designed to detect the ATXN3 repeat expansion |
| Course | Progressive and variable; cerebellar, pyramidal, extrapyramidal, peripheral nerve, eye-movement, sleep, and cognitive or mood features may occur |
| Communication | Dysarthria may change speech rate, rhythm, voice, and intelligibility; language and cognition require separate assessment |
| AAC | Planned from current need and likely change, with individual access trials and a reliable backup |
Recognition and diagnosis
Common presentations include gait or limb ataxia, dysarthria, abnormal eye movements, diplopia, spasticity, dystonia, parkinsonism, weakness, muscle wasting, cramps, altered sensation or neuropathic pain, restless legs, sleep disturbance, urinary symptoms, and fatigue. The combination changes over time and differs among people.
Diagnosis is established by identifying a pathogenic CAG repeat expansion in ATXN3. Standard sequencing or exome testing may not detect a repeat expansion, so clinicians should check that the laboratory method detects this variant type. Brain imaging can support evaluation and exclude another cause but does not establish SCA3 by itself. Predictive testing for an adult without symptoms should include genetic counseling, informed consent, psychological support, and the option not to know.
A repeat result cannot precisely predict an individual's onset, symptom pattern, or rate of progression. Family planning and testing choices are personal and should be discussed non-directively with a genetics professional.
Coordinated care and function
Care may involve an ataxia or movement-disorders neurologist, genetics, rehabilitation medicine, physical and occupational therapy, speech-language pathology, nutrition, sleep or respiratory care, neuro-ophthalmology, mental health, social work, and primary care. Review should address falls, mobility, pain, spasticity or dystonia, neuropathy, eye movement and vision, bladder function, sleep, mood, cognition, communication, swallowing, nutrition, work, driving, and caregiver needs.
Exercise, balance work, mobility equipment, orthoses, seating, home changes, and symptom medicines should be selected from assessment and the person's goals. A new focal or rapid decline should not be assumed to be SCA3 progression. Current management aims to preserve function, participation, comfort, and safety; treatment trials should not be described as established disease-modifying care.
Speech, communication, and cognition
Ataxic dysarthria may produce imprecise articulation, altered stress, variable loudness or pitch, and irregular rate. Spasticity, weakness, dystonia, respiratory support, hearing, fatigue, and medication can add to the speech profile. Intelligibility may vary by task and environment.
Assessment should establish speech, voice, language, cognition, hearing, vision, motor access, and participation. Treatment may include individualized intelligibility, pacing, breath-group, environmental, and partner strategies. High-effort voice programs are not a default for degenerative ataxia. Allow time, reduce background noise, verify key messages, and address the person directly.
Cognitive, mood, or behavior changes can occur but are not inevitable. Evaluation should consider sleep, hearing, vision, medication, fatigue, depression, anxiety, and the functional demands of the person's daily life.
Swallowing and nutrition
Dysphagia can involve oral control, chewing, timing and coordination, airway protection, or esophageal function. Ask about coughing or choking, wet or changed voice, food or pills sticking, prolonged meals, avoidance of textures, weight loss, dehydration, and chest illness; people may compensate without recognizing the extent of change.
Clinical and, when indicated, instrumental assessment should guide posture, pacing, texture, utensils, assistance, medication form, and nutrition. Decisions should balance safety, efficiency, enjoyment, autonomy, and respiratory health. The ERN-RND-endorsed ataxia guidance emphasizes repeated access to speech-language and swallowing review as needs change.
AAC and access planning
AAC may supplement speech early and become more central if intelligibility or endurance changes. Planning before a crisis allows the person to select vocabulary, learn the system, record preferred messages or voice if desired, and train partners. Speech, gesture, writing, alphabet or topic boards, and partner strategies can remain part of a multimodal plan.
Access trials should account for limb and trunk ataxia, tremor, weakness, dystonia, eye-movement limitations, vision, seating, fatigue, cognition, and progression. Touch, adapted keyboards, speech input, switches, eye tracking, or partner-assisted scanning are options to evaluate rather than stage-based defaults. Eye-movement differences can limit gaze-based access. Include health, consent, work, relationship, and emergency communication, plus a low-tech backup. See the AAC assessment and acquisition guide and ASHA AAC Practice Portal.
Prognosis and follow-up
SCA3 is progressive, but no historical subtype, ancestry, repeat result, or current device predicts an individual's exact course. Follow-up should revisit falls, respiration, sleep, nutrition, swallowing, communication, access, cognition, mental health, and participation after a meaningful change or transition. Planning should preserve the person's choices and include supported decision-making when requested.