Spinobulbar Muscular Atrophy

Collect specimen Monday-Thursday before 1430 only and not the day before a holiday. 

LAB01191

LAB01191
Mayo TC: SBULB
Mayo Test Name: Spinobulbar Muscular Atrophy (Kennedy Disease)
SBMA

3 mL Lavender (EDTA) - Whole Blood

0.5 mL 

Yellow top (ACD)

Room Temperature

Room Temp - 96 hours
All specimens will be evaluated by Mayo Clinic Laboratories for test suitability.

14-21 days

For predictive testing, it is important to first document the presence of a CAG-repeat amplification in the androgen receptor (AR) gene in an affected family member to confirm that molecular expansion is the underlying mechanism of disease in the family.
We strongly recommend that patients undergoing predictive testing receive genetic counseling both prior to testing and after results are available.
Predictive testing of an asymptomatic child is not recommended.
Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Errors in our interpretation of results may occur if information given is inaccurate or incomplete..
Current evidence suggests that the majority of individuals with spinobulbar muscular atrophy (SBMA) have a CAG-repeat expansion. However, we cannot eliminate the possibility that another type of mutation not detected by our assay is present within the AR gene.

Spinobulbar Muscular Atrophy: 
Normal alleles: 11-34 CAG repeats
Abnormal alleles: 36-62 CAG repeats

An interpretive report will be provided.

X-linked spinal and bulbar muscular atrophy (spinobulbar muscular atrophy: SBMA; or Kennedy disease) is characterized by onset of progressive muscle weakness, atrophy, and fasciculations typically in the fourth or fifth decade of life. Affected patients also have signs of androgen insensitivity such as gynecomastia, reduced fertility, and testicular atrophy. The clinical severity and age at onset can be quite variable, even within families. Because this is an X-linked disease, males manifest this disorder and females are generally asymptomatic carriers. However, there have been reports of female carriers who exhibit symptoms such as muscle weakness and cramping.
 
SBMA is caused by an expansion of the CAG trinucleotide repeat in exon 1 of the human androgen receptor (AR) gene. This trinucleotide repeat is polymorphic in the general population, with the number of repeats ranging from 11 to 34. The number of repeats found in affected individuals can range from 38 to 62. There is no consensus as to the clinical significance of alleles of 35 CAG repeats and literature suggests that alleles of 36 to 37 CAG repeats may be associated with reduced penetrance. As with other trinucleotide repeat disorders, anticipation is frequently observed and larger CAG expansions are associated with earlier onset and a more rapid clinical progression.