KENNEDY DISEASE

Spinobulbar Muscular Atrophy

DNA ANALYSIS

Spinobulbar muscular atrophy (SBMA) or Kennedy Disease (KD) is an X-linked recessive neurodegenerative disease with adult onset having an incidence of <1 in 50,000 males. Disease results from the loss of motor neurons in the brain stem and is characterized by progressive muscle weakness and atrophy and may include gynecomastia and reduced fertility in males. A molecular test is available for a complex differential diagnosis. Our test analyzes for mutations in the androgen receptor gene at Xq11-q12. The mutation responsible for SBMA is an unstable CAG trinucleotide repeat. Normal individuals have up to 34 repeats, while SBMA (KD) patients have 38 or more CAG repeats. Individuals with 35-37 CAG repeats are considered to have reduced penetrance alleles. The presence of a CAG expansion in the androgen receptor gene is virtually diagnostic of SBMA/KD.

Reasons For Referral:

Confirmation of diagnosis in symptomatic individuals.
Carrier testing for female relatives of affected individuals.
Predictive testing for individuals with a positive family history of KD. Molecular analysis of the affected relative is recommended. For asymptomatic minors, see ASHG Points to Consider*

Testing Methodology:

Direct Mutation Analysis: PCR analysis across the CAG region of the androgen receptor to determine allele size(s). All normal and expanded alleles will be detected by this assay. Allele-size ranges are subject to change as more information becomes available.

Sensitivity:

>99% detection for Kennedy Disease patients.

Specimen Requirements:

Blood: EDTA (purple-top) tubes: Adults: 14 cc; Child: 6 cc; Infant: 2-3 cc
Requisition form must accompany specimen. Prior to any genetic testing, we recommend genetic counseling and request that the subject, or their legal guardian, sign our consent form and submit it with the sample.

Turnaround Time:

3 weeks

CPT Codes and Prices:

83898, 83891, 83894, 83912

Shipping Information

Forms:

>> DNA Requisition

References:

(1995) Am. J. Hum. Genet. 57: 1233-1241*.

Test Codes:

6037