What is Spinal and Bulbar Muscular Atrophy (SBMA) or Kennedy's disease?

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Last updated: February 14, 2025 • View editorial policy

From the Guidelines

Spinal and Bulbar Muscular Atrophy (SBMA) or Kennedy's disease is a genetic disorder characterized by an expansion of CAG repeats.

Key Characteristics

  • It is one of the "CAG-repeat disorders" for which direct gene analysis is possible 1
  • Also known as Kennedy disease, it is related to other CAG-repeat disorders such as Huntington disease, spinocerebellar ataxia types 1, 2, 3, and 6, and dentatorubropallidoluysian atrophy
  • The disorder is caused by an expansion of CAG repeats within a specific gene, leading to neurodegenerative symptoms ### Diagnosis and Testing
  • Genetic testing for SBMA/Kennedy disease involves direct analysis of the CAG repeat expansion, similar to testing for other CAG-repeat disorders like Huntington disease 1
  • This testing has been available for clinical purposes since the early 1990s, with ongoing advancements in genetic testing technology ### Clinical Context
  • SBMA/Kennedy disease is a rare genetic disorder with a distinct clinical presentation, including spinal and bulbar muscular atrophy
  • Accurate diagnosis through genetic testing is essential for providing appropriate clinical care and counseling for affected individuals and their families 1

From the Research

Definition and Cause of Spinal and Bulbar Muscular Atrophy (SBMA)

  • Spinal and Bulbar Muscular Atrophy (SBMA), also known as Kennedy's disease, is a rare, adult-onset, X-linked recessive neuromuscular disease caused by expansion of a CAG repeat sequence in exon 1 of the androgen receptor gene (AR) encoding a polyglutamine (polyQ) tract 2, 3, 4, 5.
  • The polyQ-expanded AR accumulates in nuclei, and initiates degeneration and loss of motor neurons and dorsal root ganglia 2.

Clinical Characteristics

  • The disease is characterized by muscle weakness and atrophy localized proximally in the limbs, and bulbar involvement 2, 3, 6.
  • Sensory disturbances are associated with the motor phenotype, but may be subclinical 2.
  • The most frequent systemic symptom is gynecomastia related to androgen insensitivity, but other abnormalities, such as heart rhythm and urinary disturbances, have also been reported 2.

Diagnosis and Treatment

  • The diagnosis of SBMA is based on genetic testing, with 38 CAG repeats taken as pathogenic 2.
  • Despite several therapeutic attempts made in mouse models, no effective disease-modifying therapy is yet available, although symptomatic therapy is beneficial for the management of the weakness, fatigue and bulbar symptoms 2, 5.
  • Pharmacological inhibition of the toxic accumulation of mutant AR is a potential therapy for SBMA, with leuprorelin showing promise in clinical trials 5.

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.