Machado-Joseph Disease:

Spinocerebellar Ataxia Type 3 (SCA3) 

Machado-Joseph disease (MJD) also known as spinocerebellar ataxia type 3 (SCA3) is an autosomal dominant neurodegenerative disorder, located on chromosome 14q24.3, that is characterized by progressive cerebellar ataxia, peripheral nerve palsy, ophthalmoplegia, facial fasciculation and bulging eyes.  However, variations can closely resemble other spinocerebellar ataxia types, dentatorubral-pallidoluysian atrophy, or Huntington disease.

MJD has an onset between 30 and 50 years of age but juvenile cases have been described.  The disease also displays anticipation resulting in earlier onset with each generation. MJD is in the class of trinucleotide repeat conditions in which there is an inappropriate expansion of a CAG repeat in the gene.  The unaffected population has between 13 and 36 CAG repeats.  Affected patients have more than 65 repeats.

REASONS FOR REFERRAL:

• Confirmatory testing for individuals who may be exhibiting symptoms.

• Individuals at risk of inheriting MJD who want to determine their risk of SCA3.

• Individuals at risk who wish prenatal diagnosis.

• For ambiguous patients, this test may be ordered as part of a Neurological Panel or SCA Panel.

TESTING METHODOLOGY

• Fluorescent PCR sizing of the CAG region of the gene.

SPECIMEN REQUIREMENTS:

• Blood EDTA (purple top) tubes:  

            Newborn: minimum 1-2 mL          

            Child/Adult: prefer 2 tubes of 3-5 mL

• Prenatal testing: Please contact the laboratory for instructions.

TURNAROUND TIME:  10 working days

CPT CODES: