Spino-bulbar muscular atrophy test
10-20 mL blood in EDTA tube.
PCR-based analysis to detect an expanded triplet repeat mutation in the androgen receptor (AR) gene.
Used for definitive diagnosis in symptomatic males.
Used to define carrier status in female relatives of affected males.
Predictive tests in asymptomatic males should only be arranged in consultation with the pathologist and a clinical genetics service.
Prenatal diagnosis may be available if the mother carries an identified mutation.
In the normal population the triplet repeat region in the AR gene is less than 40 triplets long (120 nucleotides).
An expanded triplet repeat accounts for almost all cases of spino-bulbar muscular atrophy.
The identification of a mutation is diagnostic of spino-bulbar muscular atrophy (symptomatic male) or of carrier status (asymptomatic female).
The identification of this mutation does not predict the severity or age of onset of the disorder. This test does not distinguish between asymptomatic and affected individuals.
Molecular genetic studies may be indicated in other family members.
Muller U et al. >i>J Neurol Sci 1994; 124: 119-140.
La Spada AR et al. Ann Neurol 1994; 36: 814-822.