Machado-Joseph disease type 2

Machado-Joseph disease type 2 (MJD type 2), also known as spinocerebellar ataxia type 3 (SCA3) type 2 or the intermediate/cerebellar phenotype of MJD, is a subtype of Machado-Joseph disease, the most common autosomal dominant spinocerebellar ataxia worldwide. MJD is caused by an abnormal CAG trinucleotide repeat expansion in the ATXN3 gene on chromosome 14q32.1, which encodes an expanded polyglutamine tract in the ataxin-3 protein. MJD type 2 represents the most common clinical presentation of MJD and is characterized by a predominantly cerebellar and pyramidal syndrome. The CAG repeat length in type 2 typically falls in an intermediate range (approximately 73–80 repeats), correlating with a moderate age of onset. The disease primarily affects the central nervous system, particularly the cerebellum, brainstem, and spinal cord. Key clinical features of MJD type 2 include progressive cerebellar ataxia (impaired coordination and balance), pyramidal signs such as spasticity and hyperreflexia, and progressive external ophthalmoplegia (difficulty moving the eyes). Unlike MJD type 1, which has a more aggressive course with prominent dystonia and rigidity, type 2 tends to have a somewhat later onset (typically in the third to fifth decade of life) and a more purely cerebellar presentation. Patients may also experience dysarthria (slurred speech), dysphagia (difficulty swallowing), and nystagmus. Peripheral neuropathy and amyotrophy may be present but are less prominent than in MJD type 3. There is currently no cure or disease-modifying treatment for Machado-Joseph disease type 2. Management is supportive and symptomatic, including physical therapy and rehabilitation to maintain mobility, speech therapy for dysarthria, occupational therapy, and assistive devices. Spasticity may be managed with medications such as baclofen. Genetic counseling is recommended for affected families. Research into potential therapies, including antisense oligonucleotides and gene silencing strategies targeting the ATXN3 gene, is ongoing but remains investigational.

Common questions about Machado-Joseph disease type 2