Spinobulbar Muscular Atrophy

(SBMA/Kennedy’s Disease)

Increased SBMA Prevalence & Founder Effect Linked to a Common Ancestral Haplotype

Spinobulbar muscular atrophy (SBMA), or Kennedy’s Disease, is a rare genetic disorder that causes progressive muscle weakness.

Research in western Canada has found a significantly higher prevalence of SBMA in Indigenous populations, particularly among Saulteaux individuals, compared to the global average.

People with SBMA often experience:

  • Muscle weakness that affects walking

  • Difficulty speaking clearly

  • Swallowing problems, increasing the risk of choking

  • Breathing difficulties as the disease progresses

These challenges can impact daily life, independence, social interactions, and overall well-being.

Research Team: Jamie Leckie, Matthew M. Joel, Kristina Martens, Alexandra King, Malcolm King, Lawrence W. Korngut, A.P. Jason de Koning, Gerald Pfeffer*, Kerri L. Schellenberg*

Affliations: Hotchkiss Brain Institute, Department of Clinical Neurosciences
Alberta Child Health Research Institute, Department of Medical Genetics
Cumming School of Medicine, University of Calgary
College of Medicine, University of Saskatchewan

For more information please contact:

Dr. Gerald Pfeffer – gerald.pfeffer@ucalgary.ca

Quick Facts

  • Who it affects: Primarily males, as it is linked to the X chromosome

  • Cause: A trinucleotide expansion in the androgen receptor (AR) gene

  • Symptoms: Progressive muscle weakness, difficulty speaking, swallowing, and breathing, tongue wasting, and reduced fertility.

    • SBMA typically develops between ages 30 and 50 but can appear as early as 15 or as late as 60. While it primarily affects men, women who inherit the gene may also experience symptoms.

  • Other impacts: May also affect metabolism, heart function, and sensation in some individuals

Terms to Know

  • A gene that provides instructions for making a protein called the androgen receptor, which binds to male hormones (androgens). Mutations in this gene, specifically trinucleotide CAG repeat expansions, are the cause of SBMA.

  • Difficulty in articulating words due to muscle weakness affecting the speech muscles, a common symptom in SBMA.

  • Difficulty swallowing, which can result from weakness in the muscles involved in swallowing, frequently seen in SBMA patients

  • A group of genes inherited together from a single parent, often used in genetic research to trace ancestry and disease inheritance.

  • Nerve cells responsible for transmitting signals from the brain and spinal cord to muscles, enabling movement. In SBMA, these neurons degenerate, leading to muscle weakness.

  • A group of genetic diseases causing progressive muscle weakness and degeneration.

  • Muscles controlled by the brainstem (bulbar region), including those involved in speaking, swallowing, and breathing. Degeneration of neurons affecting these muscles leads to bulbar symptoms in SBMA

    • Kennedy's Disease: Named after Dr. William R. Kennedy, who first identified the condition in the 1960s.

    • Spinal and Bulbar Muscular Atrophy (SBMA): A term describing the degeneration of spinal and bulbar motor neurons.

    • Bulbo-Spinal Atrophy: Emphasizes the sequential involvement of bulbar and spinal regions.

    • X-Linked Bulbospinal Neuropathy (XBSN): Reflects the genetic transmission pattern of the disease.

    • X-Linked Spinal Muscular Atrophy Type 1 (SMAX1): An alternative classification based on genetic linkage.

  • A mutation where a sequence of three nucleotides (CAG, in the case of SBMA) is repeated more times than normal in a gene. This expansion can disrupt normal protein function, leading to disease.

What We’ve Learned about SBMA in Indigenous Communities

  • Prevalence in Saskatchewan Indigenous communities: 14.7 per 100,000 people

  • Prevalence in Saulteaux individuals: 184 per 100,000—the highest known globally

  • Global comparison: Most regions report only 1-2 cases per 100,000

  • Implications on diagnosis and care: Cases may be underreported due to barriers in healthcare access, bias, and misdiagnosis, as symptoms can resemble other conditions.

  • Diagnostic delays: often averaging 10 years, can prevent early support and management.

Estimates of Indigenous SBMA in neuromuscular referral centres

What we are Doing Currently

  • Expanding research participation to improve prevalence estimates

  • Understanding how genes influence symptoms and disease progression

  • Enhancing healthcare provider knowledge for better screening and support

  • Encouraging genetic testing to reduce diagnostic delays

What to Learn More?

Scroll to the bottom of this page to check out some of our recent publications and learning resources

Ongoing Projects

Exploring SBMA in Indigenous Communities – Muscular Dystrophy Canada

  • Examining the impact of SBMA through community-driven research

  • Using photovoice to capture lived experiences and facilitate discussion

  • Aims to improve awareness and resource access for affected individuals

Indigenous Perspectives on SBMA and Translational Research (NFRF-E)

  • Identifying genetic links and historical factors influencing SBMA prevalence

  • Exploring gene therapy options while ensuring culturally safe research practices

  • Engaging affected communities in study design and implementation

SBMA in Prairie Provinces: Clinical and Community Needs (CIHR)

  • Strengthening clinical knowledge and therapy development

  • Conducting a photovoice study to amplify Indigenous experiences

  • Collaborating with specialists across Canada to enhance diagnosis and care

This work is supported by:

  • Katherine Sarah Melinda Mei-Ling Thomas Rare Diseases Scholarship (MMJ)

  • CFI JELF Grant, CSM Clinical Research Fund Seed Grant

  • Muscular Dystrophy Canada (Funding to GP)

  • IPHCPR Network knowledge mobilization support

Check out Publications, Reports and More!

SBMA is significantly more common among Indigenous populations in Saskatchewan than previously estimated, largely due to a founder effect. The research team examined patient data from the Saskatoon neuromuscular clinic and conducted genetic haplotype analyses, estimating a prevalence of 14.7 per 100,000 among persons of Indigenous descent—far above the global estimate of 1–2 per 100,000. The study found that most affected individuals share a unique haplotype, indicating a founder effect dating back roughly 10 generations (approximately 250 years). These findings suggest that SBMA is underdiagnosed due to delayed testing and limited healthcare access, speaking to the need for enhanced screening, improved genetic counseling, and targeted community outreach.

🔗 Click here to read the full study

Reference: Leckie JN, Joel MM, Martens K, King A, King M, Korngut LW, de Koning APJ, Pfeffer G, Schellenberg KL. Highly Elevated Prevalence of Spinobulbar Muscular Atrophy in Indigenous Communities in Canada Due to a Founder Effect. Neurol Genet. 2021;7:e607.

Higher-Than-Expected SBMA Cases in Western Canada, particularly among Indigenous populations. In this follow up research, the team analyzed diagnostic testing data from 2018 to 2023 and identified 59 new cases in Alberta, Saskatchewan, and the Northwest Territories. These numbers suggest SBMA is significantly underdiagnosed, likely due to healthcare access barriers and diagnostic delays. The findings reinforce the need for increased awareness, improved screening, and better genetic counseling to support affected individuals and their families.

🔗 Click here to read the full study

Reference: Lamont R, King M, King A, Schellenberg K, Pfeffer G. Higher than expected incident cases of spinal bulbar muscular atrophy in western Canada. Brain. 2024;147:e43–e44.

Clinical Screening Guidelines – COMING SOON!