What is Machado-Joseph Disease

TL;DR: Machado-Joseph Disease (also known as Spinocerebellar Ataxia Type 3) is a progressive, inherited neurodegenerative disorder primarily characterized by problems with movement, balance, and coordination. It is caused by a genetic mutation that leads to the accumulation of abnormal proteins in the brain, and currently, there is no cure, though supportive therapies can help manage symptoms.

What is Machado-Joseph Disease?

Machado-Joseph Disease (MJD), or Spinocerebellar Ataxia Type 3 (SCA3), is a rare, autosomal dominant genetic condition that affects the central nervous system. It is the most common form of dominantly inherited ataxia worldwide. The condition primarily targets the cerebellum, brainstem, and spinal cord, leading to a gradual decline in motor control. Within the DiseaseMaps community, 42 people with Machado-Joseph Disease have already joined to share their experiences, highlighting the importance of peer support in navigating this complex diagnosis.

What are the primary symptoms and body systems affected?

Because Machado-Joseph Disease impacts multiple areas of the brain, symptoms can be diverse and vary significantly between individuals, even within the same family. The condition typically affects the following systems:

• Motor System: Progressive gait instability, uncoordinated limb movements (ataxia), and muscle stiffness (spasticity).


• Ocular System: Difficulty with eye movements, double vision, and bulging eyes.


• Neurological/Sensory: Peripheral neuropathy, which causes numbness or tingling in the extremities, and sometimes involuntary facial or tongue movements (fasciculations).


• Speech and Swallowing: Dysarthria (slurred or slow speech) and dysphagia (difficulty swallowing) are common as the disease progresses.

How is Machado-Joseph Disease classified?

Clinicians often classify Machado-Joseph Disease into three major clinical types based on the age of onset and the predominant symptoms:

1. Type I: Early onset (usually teens to 30s) characterized by rapid progression, severe muscle stiffness, and significant dystonia.


2. Type II: The most common form, with onset in the 30s to 50s, primarily marked by classic ataxia, spasticity, and eye movement abnormalities.


3. Type III: Later onset (often 40s to 70s) where peripheral neuropathy and muscle wasting are the most prominent features, with milder cerebellar symptoms.

What causes Machado-Joseph Disease and is it hereditary?

Machado-Joseph Disease is caused by a "CAG trinucleotide repeat" expansion in the ATXN3 gene. This mutation leads to the production of an abnormal protein called ataxin-3, which clumps together and damages nerve cells. Because it is an autosomal dominant condition, an individual only needs one copy of the mutated gene from one parent to inherit the disease. There is a 50% chance of passing the mutation to each child. A unique aspect of MJD is "anticipation," where the number of genetic repeats can increase in successive generations, often leading to earlier onset and more severe symptoms in children compared to their parents.

How common is this condition?

While exact global prevalence is difficult to determine due to underdiagnosis, Machado-Joseph Disease is recognized as the most common hereditary ataxia. Prevalence varies significantly by geography; for instance, it is notably higher in populations with Portuguese ancestry, particularly those from the Azores islands, where the prevalence is estimated to be approximately 1 in 4,000.

Next steps

• Consult a Neurologist: Seek a specialist in movement disorders or a neurogeneticist to confirm a diagnosis through genetic testing.


• Physical and Occupational Therapy: Engage with therapists early to maintain mobility and develop strategies for daily living.


• Join a Support Group: Connect with others at DiseaseMaps.org to share coping strategies and stay informed about current research.


• Genetic Counseling: Speak with a counselor to understand the implications of the genetic mutation for family planning and testing.

Medical Disclaimer: This content is for informational purposes only and does not constitute professional medical advice, diagnosis, or treatment; always seek the advice of your physician or other qualified health provider with any questions regarding a medical condition.

References

• NIH Genetic and Rare Diseases Information Center (GARD): Machado-Joseph disease.


• Orphanet: Spinocerebellar ataxia type 3 (ORPHA:125).


• OMIM (Online Mendelian Inheritance in Man): Machado-Joseph disease (#109150).


• National Ataxia Foundation (NAF): Resources and support for SCA3/MJD.