Is Machado-Joseph Disease hereditary?

Machado-Joseph Disease, also known as Spinocerebellar Ataxia Type 3 (SCA3), is a strictly hereditary, genetic condition caused by an expansion of a CAG trinucleotide repeat in the ATXN3 gene. Because it follows an autosomal dominant inheritance pattern, an individual with the disease has a 50% chance of passing the genetic mutation to each of their children.

Is Machado-Joseph Disease hereditary or genetic?

Machado-Joseph Disease is both genetic and hereditary. It is genetic because it is caused by a specific alteration in the DNA sequence of the ATXN3 gene on chromosome 14. It is hereditary because this mutation is passed down through families from one generation to the next. In clinical genetics, we classify this as an autosomal dominant disorder. This means that a person only needs to inherit one copy of the mutated gene from one affected parent to develop the condition. Unlike some other genetic conditions, de novo (spontaneous) mutations are extremely rare in Machado-Joseph Disease; almost all cases are inherited from an affected parent.

What is the risk to family members?

Because Machado-Joseph Disease is autosomal dominant, the inheritance risk is straightforward in terms of probability. If one parent carries the expanded ATXN3 gene, each of their children has a 50% statistical probability of inheriting the mutation. It is important to note that while the inheritance of the gene is certain if passed down, the age of onset and the severity of symptoms can be influenced by the length of the CAG repeat expansion. Longer expansions often correlate with an earlier onset of Machado-Joseph Disease symptoms, a phenomenon known as genetic anticipation.

How is genetic testing performed for Machado-Joseph Disease?

Genetic testing for Machado-Joseph Disease is highly accurate and is performed via a blood test that analyzes the ATXN3 gene for the expanded CAG repeat. Clinical geneticists generally recommend testing in the following scenarios:

• Diagnostic testing: For individuals currently presenting with symptoms such as progressive ataxia, spasticity, or muscle weakness, to confirm a clinical suspicion.


• Predictive testing: For asymptomatic adults who have a family history of Machado-Joseph Disease and wish to know their own genetic status.


• Reproductive planning: For couples who know they carry the mutation and wish to discuss options such as preimplantation genetic testing (PGT) or prenatal diagnosis.

Why is genetic counseling essential?

Genetic counseling is a critical component of the care pathway for Machado-Joseph Disease. Because this is a progressive, neurodegenerative condition for which there is currently no cure, the decision to undergo predictive testing is deeply personal and complex. A genetic counselor helps families navigate the psychological impact of these results, discusses the implications for insurance and employment, and explains the nuances of reproductive choices, including the possibility of testing embryos during IVF to prevent transmission to future generations. Within our community at DiseaseMaps.org, 42 people with Machado-Joseph Disease have shared their experiences, highlighting the value of connecting with others who have navigated these same complex genetic decisions.

Next steps

• Consult with a board-certified clinical geneticist or neurologist specializing in movement disorders to discuss testing options.


• Request a referral to a genetic counselor to discuss the implications of your family history and potential reproductive options.


• Connect with the DiseaseMaps.org community to learn how others have managed the diagnostic and emotional journey of living with Machado-Joseph Disease.


• Review resources from the National Ataxia Foundation for specialized support and information on ongoing clinical research.

Medical disclaimer: This information is for educational purposes only and does not replace 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

• National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD): Machado-Joseph Disease.


• Orphanet: Spinocerebellar ataxia type 3 (ORPHA: 3343).


• Online Mendelian Inheritance in Man (OMIM): Spinocerebellar Ataxia 3; SCA3 (Entry #109150).


• National Ataxia Foundation (NAF): Understanding Machado-Joseph Disease/SCA3.