Spinobulbar Muscular Atrophy (Kennedy Disease), Molecular Analysis, Varies

Casandra

Casandra Test Code MC50129Version 1 (DRAFT)

Performing Lab

Lab Mayo Clinic LabLab Test ID SBULBCPT Code 81204

Spinobulbar Muscular Atrophy (Kennedy Disease), Molecular Analysis, Varies

Clinical Use

Use

Spinobulbar muscular atrophy (SBMA), also known as Kennedy disease, is characterized by progressive muscle weakness, atrophy, and fasciculations typically manifesting in the fourth or fifth decade of life. This condition is linked to androgen insensitivity, with affected patients often exhibiting gynecomastia, reduced fertility, and testicular atrophy. Due to its X-linked inheritance pattern, males generally express the disorder, while females are asymptomatic carriers. The disease is caused by an expansion of a CAG trinucleotide repeat in the AR gene. The number of repeats correlates with disease severity and onset age, with larger expansions associated with earlier onset and faster progression.

Special Instructions

For individuals with a family history of SBMA and a documented expansion in the AR gene, presymptomatic testing is available. The use of this test is most appropriate when there is clinical suspicion of sporadic or familial SBMA. It's important for candidates undergoing predictive testing to engage in genetic counseling both before and after testing. New York Clients should ensure that informed consent for genetic testing is documented.

Limitations

The test may not detect other mutations within the AR gene not related to CAG-repeat expansion. Predictive testing in asymptomatic children is not recommended. The presence of a CAG-repeat expansion must first be documented in an affected family member to confirm the molecular basis of the disease. Improper specimen handling could interfere with test results. DNA yield and quality are crucial factors; specimens not meeting these criteria may result in test cancellation.

Test Details

New York Approved