Machado-Joseph disease type 3

Machado-Joseph disease type 3 (MJD type 3), also known as spinocerebellar ataxia type 3 (SCA3) type 3 or Joseph disease, is the mildest and latest-onset subtype of Machado-Joseph disease. Machado-Joseph disease is the most common autosomal dominant spinocerebellar ataxia worldwide and is caused by an expanded CAG trinucleotide repeat in the ATXN3 gene on chromosome 14q32.1, which encodes the protein ataxin-3. The number of CAG repeats in MJD type 3 tends to be at the lower end of the pathological range (approximately 60–70 repeats), which correlates with the later age of onset and milder clinical presentation compared to types 1 and 2. MJD type 3 primarily affects the nervous system, particularly the cerebellum and peripheral nerves. The hallmark features of this subtype include progressive cerebellar ataxia (difficulty with coordination and balance), peripheral neuropathy, and prominent distal muscle atrophy and weakness. Patients may also develop generalized areflexia (loss of reflexes). Unlike the more severe MJD subtypes, type 3 patients typically have less prominent pyramidal signs and extrapyramidal features such as dystonia or rigidity. Some patients may also experience mild ophthalmoplegia (impaired eye movements) and fasciculations. The disease onset is generally in the 40s to 60s, and progression tends to be slower than in types 1 and 2. There is currently no cure or disease-modifying treatment for Machado-Joseph disease type 3. Management is supportive and symptomatic, including physical therapy and rehabilitation to maintain mobility, occupational therapy, speech therapy for dysarthria, and assistive devices as the disease progresses. Pharmacological treatments may be used to manage specific symptoms such as spasticity, pain from neuropathy, or sleep disturbances. Genetic counseling is recommended for affected families. Research into potential therapies, including antisense oligonucleotides and gene silencing strategies targeting the expanded ATXN3 gene, is ongoing.

Common questions about Machado-Joseph disease type 3