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Test ID: SBULB Spinobulbar Muscular Atrophy (Kennedy Disease), Molecular Analysis, Varies

Reporting Name

Spinobulbar Musc Atrophy, Kennedy's

Useful For

Molecular confirmation of clinically suspected cases of sporadic or familial spinobulbar muscular atrophy (SBMA)

 

Presymptomatic testing for individuals with a family history of SBMA and a documented expansion in the androgen receptor (AR) gene

Clinical Information

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.

Interpretation

An interpretive report will be provided.

Testing Algorithm

See Inherited Motor Neuron Disease Testing Algorithm in Special Instructions.

Analytic Time

5 days

Day(s) and Time(s) Performed

Tuesday; 10 a.m.

Clinical Reference

Pinsky L, Beitel LK, Trifiro MA: Spinobulbar Muscular Atrophy. In The Metabolic and Molecular Basis of Inherited Disease. Vol 4. 8th edition. Edited by CR Scriver. AL Beaudet, WS Sly, et al. New York, McGraw-Hill Book Company, 2001, pp 4147-4157

Method Name

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

Specimen Type

Varies


Shipping Instructions


Specimen preferred to arrive within 96 hours of draw.



Specimen Required


Patient Preparation: A previous bone marrow transplant from an allogenic donor will interfere with testing. Call 800-533-1710 for instructions for testing patients who have received a bone marrow transplant.

Specimen Type: Whole blood

Container/Tube:

Preferred: Lavender top (EDTA) or yellow top (ACD)

Acceptable: Any anticoagulant

Specimen Volume: 3 mL

Collection Instructions:

1. Invert several times to mix blood.

2. Send specimen in original tube.


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Varies Ambient (preferred)
  Frozen 
  Refrigerated 

Reference Values

Normal alleles: 11-34 CAG repeats

Abnormal alleles: 36-62 CAG repeats

 

An interpretive report will be provided.

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

81204-AR (androgen receptor)(eg, spinal and bulba muscular atrophy, Kennedy disease, X chromosome inactivation) gene analysis; characterization of alleles (eg, expanded size or methylation status)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
SBULB Spinobulbar Musc Atrophy, Kennedy's In Process

 

Result ID Test Result Name Result LOINC Value
53341 Result Summary 50397-9
53342 Result 82939-0
53343 Interpretation 69047-9
53344 Reason for Referral 42349-1
53345 Specimen 31208-2
53346 Source 31208-2
53348 Released By 18771-6

Forms

1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available in Special Instructions:

-Informed Consent for Genetic Testing (T576)

-Informed Consent for Genetic Testing-Spanish (T826)

2. Molecular Genetics: Neurology Patient Information in Special Instructions

3. If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen.