Machado-Joseph disease type 1

Machado-Joseph disease type 1 (MJD type 1), also known as spinocerebellar ataxia type 3 (SCA3) type 1, is the most severe subtype of Machado-Joseph disease. MJD is the most common autosomal dominant spinocerebellar ataxia worldwide. It is caused by an abnormal CAG trinucleotide repeat expansion in the ATXN3 gene on chromosome 14q32.1, which encodes the protein ataxin-3. Type 1 (also referred to as the 'Joseph' phenotype) is characterized by the earliest age of onset among MJD subtypes, typically presenting in the teens to early twenties, and is generally associated with larger CAG repeat expansions (approximately 73–86 repeats). Machado-Joseph disease type 1 primarily affects the nervous system, particularly the cerebellum, brainstem, basal ganglia, and spinal cord. Key clinical features of this subtype include progressive cerebellar ataxia (impaired coordination and balance), prominent pyramidal signs (spasticity, hyperreflexia), and extrapyramidal features (dystonia, rigidity, bradykinesia). Patients may also exhibit progressive external ophthalmoplegia (limited eye movements), bulging eyes (lid retraction), facial and lingual fasciculations, and dysphagia. The disease tends to progress more rapidly than other MJD subtypes, and patients often become wheelchair-dependent within a relatively short period. There is currently no cure or disease-modifying treatment for Machado-Joseph disease type 1. Management is supportive and symptomatic, including physical therapy to maintain mobility, occupational therapy, speech therapy for dysarthria and dysphagia, and pharmacological treatment for spasticity and dystonia. Genetic counseling is recommended for affected families. Research into potential therapies, including antisense oligonucleotides and gene silencing strategies targeting the mutant ATXN3 gene, is ongoing but remains investigational.

Common questions about Machado-Joseph disease type 1