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HelpTest ID: SBULB Spinobulbar Muscular Atrophy (Kennedy Disease), Molecular Analysis, Varies
Reporting Name
Spinobulbar Musc Atrophy, Kennedy'sUseful 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.
Spinobulbar muscular atrophy 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
The interpretive report includes an overview of the findings as well as the associated clinical significance.
Testing Algorithm
For information see Inherited Motor Neuron Disease and Dementia Testing Algorithm
Report Available
14 to 21 daysDay(s) Performed
Varies
Clinical Reference
1. Pinsky L, Beitel LK, Trifiro MA: Spinobulbar Muscular Atrophy. In Scriver CR, Beaudet AL, Sly WS, et al. The Metabolic and Molecular Basis of Inherited Disease. Vol 4. 8th ed. McGraw-Hill Book Company, 2001;4147-4157
2. Breza M, Koutsis G. Kennedy's disease (spinal and bulbar muscular atrophy): a clinically oriented review of a rare disease. J Neurol. 2019;266(3):565-573. doi:10.1007/s00415-018-8968-7
Method Name
Polymerase Chain Reaction (PCR)
Specimen Type
VariesSpecimen Required
Patient Preparation: A previous bone marrow transplant from an allogenic donor will interfere with testing. For information about testing patients who have received a bone marrow transplant, call 800-533-1710.
Specimen Type: Whole blood
Container/Tube:
Preferred: Lavender top (EDTA) or yellow top (ACD)
Acceptable: None
Specimen Volume: 3 mL
Collection Instructions:
1. Invert several times to mix blood.
2. Send whole blood specimen in original tube. Do not aliquot.
Specimen Stability Information: Ambient (preferred) 4 days/Refrigerated 4 days/Frozen 4 days
Additional Information:
1. Specimens are preferred to be received within 4 days of collection. Extraction will be attempted for specimens received after 4 days, and DNA yield will be evaluated to determine if testing may proceed.
2. To ensure minimum volume and concentration of DNA is met, the requested volume must be submitted. Testing may be canceled if DNA requirements are inadequate.
Specimen Type: Extracted DNA
Container/Tube:
Preferred: Screw Cap Micro Tube, 2mL with skirted conical base
Acceptable: Matrix tube, 1mL
Collection Instructions:
1. The preferred volume is at least 100 mcL at a concentration of 75 ng/mcL.
2. Include concentration and volume on tube.
Specimen Stability Information: Frozen (preferred) 1 year/Ambient/Refrigerated
Additional Information: DNA must be extracted in a CLIA-certified laboratory or equivalent and must be extracted from a specimen type listed as acceptable for this test (including applicable anticoagulants). Our laboratory has experience with Chemagic, Puregene, Autopure, MagnaPure, and EZ1 extraction platforms and cannot guarantee that all extraction methods are compatible with this test. If testing fails, one repeat will be attempted, and if unsuccessful, the test will be reported as failed and a charge will be applied. If applicable, specific gene regions that were unable to be interrogated due to DNA quality will be noted in the report.
Specimen Minimum Volume
See Specimen Required
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Varies | Varies | |
Special Instructions
Reference Values
Normal alleles: 11-34 CAG repeats
Abnormal alleles: 36-62 CAG repeats
The interpretive report includes an overview of the findings as well as the associated clinical significance.
Test Classification
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US 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 | 35359-9 |
| 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:
-Informed Consent for Genetic Testing (T576)
-Informed Consent for Genetic Testing-Spanish (T826)
2. Molecular Genetics: Neurology Patient Information
3. If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen.
mml-Neuromuscular