Yale New Haven Hospital

Department of Laboratory Medicine
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Spinobulbar muscular atrophy

Lab Section: 

Sendout Reference


Lab Location: 


Reference Lab: 



Test ID: 




Kennedy's Disease


A Polymerase Chain Reaction (PCR)-based assay is utilized to detect expansion-type mutations (CAG repeats) within the androgen receptor gene.


Tuesdays, 10 am


15 days

Specimen Requirements: 

Collection: 3.0 mL Blood in a Lavender Top Tube.
Pediatric volume: 0.5 mL.
Whole blood; Lavender top (EDTA) or yellow top (ACD)
Transport: Ambient.
Handling: Specimen must arrive within 96 hours of draw.
Unacceptable conditions: No specimen should be rejected. If specimen is received in wrong anticoagulant or at an inappropriate temperature, include note to laboratory. If questions, contact laboratory.



Clinical Indications: 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.

Reference Interval: 

See patient report or consult reference laboratory website.


CPT Code(s): 


Last Changed: 

8/23/2017 5:34:58 PM

Last Reviewed: 

8/23/2017 5:35:06 PM