Hypermobility Spectrum Disorder (HMS): Causes, Symptoms, and Management

What causes HMS?

Hypermobility Spectrum Disorder (HMS), often referred to as hypermobility, is primarily caused by an inherited genetic predisposition affecting the body's connective tissues, particularly collagen, leading to increased joint laxity and reduced structural integrity.

Understanding Hypermobility Spectrum Disorder (HMS)

Hypermobility Spectrum Disorder (HMS), or Hypermobility Spectrum Disorder (HSD) as it's more formally known in clinical circles, describes a condition where joints move beyond the typical, healthy range of motion. While many individuals possess generalized joint hypermobility (GJH) without symptoms, HMS/HSD specifically refers to the presence of musculoskeletal symptoms (e.g., pain, instability, subluxations/dislocations) directly attributable to this increased laxity. It's crucial to distinguish between benign joint hypermobility and the symptomatic, often debilitating, condition of HMS/HSD.

The Primary Cause: Genetic Predisposition

The root cause of HMS/HSD lies overwhelmingly in genetics. It is a hereditary condition, meaning it can be passed down through families. The genetic alterations primarily impact the structure and function of connective tissues throughout the body.

• Connective Tissue Composition: Connective tissues, such as ligaments, tendons, fascia, and joint capsules, are rich in proteins like collagen and elastin. These proteins provide strength, structure, and elasticity to tissues.
• Collagen Abnormalities: In individuals with HMS/HSD, there are often subtle, or sometimes significant, abnormalities in the genes responsible for producing collagen, particularly Type I, III, and V collagen. These genetic variations can lead to collagen fibers that are less robust, more elastic, or improperly organized.
• Elastin Properties: Similarly, alterations in elastin, the protein responsible for elasticity, can contribute to tissues that stretch too easily and return to their original shape less effectively.

This inherent "looseness" of the connective tissues directly translates to laxity in the ligaments and joint capsules, allowing joints to extend or articulate beyond their normal physiological limits.

Specific Genetic Conditions Associated with HMS

While HMS/HSD itself is a diagnosis of exclusion (meaning other specific connective tissue disorders must be ruled out), it shares many characteristics with, and is considered part of, a broader group of heritable connective tissue disorders. Some well-known conditions that feature significant hypermobility include:

• Ehlers-Danlos Syndromes (EDS): This is a group of inherited connective tissue disorders, with hypermobile Ehlers-Danlos Syndrome (hEDS) being the most common type. hEDS is characterized by generalized joint hypermobility, chronic pain, and a range of other systemic manifestations. The exact genetic cause of hEDS is still largely unknown, but it is clearly inherited.
• Marfan Syndrome: Caused by mutations in the FBN1 gene, which codes for fibrillin-1, a protein essential for the formation of elastic fibers in connective tissue. This leads to issues in the skeletal, ocular, and cardiovascular systems, often including significant joint hypermobility.
• Loeys-Dietz Syndrome: A more severe connective tissue disorder caused by mutations in genes related to the transforming growth factor beta (TGFβ) signaling pathway. It presents with arterial aneurysms, skeletal abnormalities, and often joint hypermobility.
• Osteogenesis Imperfecta (OI): While primarily known for brittle bones, some types of OI (e.g., Type I) can also present with joint hypermobility due to defects in Type I collagen.

Contributing Factors and Mechanisms

Beyond the primary genetic basis, several mechanisms contribute to the manifestation and impact of HMS/HSD:

• Abnormal Collagen Structure and Synthesis: The genetic mutations lead to the production of collagen that is either quantitatively insufficient or qualitatively inferior. This affects the tensile strength and integrity of ligaments, tendons, and joint capsules.
• Elastin Content and Function: Changes in elastin can result in tissues that are excessively stretchy, further compromising joint stability.
• Proprioceptive Impairment: Individuals with hypermobile joints often have reduced proprioception (the body's sense of its position in space). This is thought to be due to less tension in the joint capsules and ligaments, which contain mechanoreceptors that feed information back to the brain. Poor proprioception can lead to awkward movements, increased risk of injury, and difficulty stabilizing joints.
• Muscle Weakness and Imbalance: While not a primary cause, secondary muscle weakness or imbalances around hypermobile joints can exacerbate instability and pain. Muscles often work harder to compensate for lax ligaments, leading to fatigue and protective guarding.
• Joint Capsule and Ligament Laxity: This is the direct biomechanical consequence of the connective tissue abnormalities. The "sleeves" (joint capsules) and "ropes" (ligaments) that normally hold the joint together are too loose, allowing for excessive movement.

Symptoms and Associated Conditions

The hypermobility of joints can lead to a wide array of symptoms and associated conditions, extending beyond simple joint pain:

• Musculoskeletal Pain: Chronic widespread pain, often disproportionate to activity.
• Joint Instability: Frequent subluxations (partial dislocations) or full dislocations.
• Fatigue: Often debilitating, not relieved by rest.
• Soft Tissue Injuries: Increased susceptibility to sprains, strains, and tendinopathies.
• Autonomic Dysfunction (Dysautonomia): Conditions like Postural Orthostatic Tachycardia Syndrome (POTS) are common, causing dizziness, palpitations, and fainting.
• Gastrointestinal Issues: Dysmotility, reflux, and irritable bowel syndrome (IBS)-like symptoms.
• Skin Manifestations: Soft, velvety, or stretchy skin, easy bruising.
• Pelvic Floor Dysfunction: Incontinence or prolapse.

Diagnosis and Clinical Assessment

Diagnosis of HMS/HSD involves a comprehensive clinical evaluation. The Beighton Score is a widely used screening tool to quantify generalized joint hypermobility, assessing the flexibility of five specific joints bilaterally. However, a high Beighton score alone is not sufficient for diagnosis; the presence of chronic musculoskeletal symptoms and the exclusion of other specific connective tissue disorders are critical. A thorough medical history, physical examination, and sometimes genetic testing (to rule out other conditions) are essential.

Management and Exercise Considerations

While the genetic cause of HMS/HSD cannot be changed, effective management strategies focus on symptom alleviation and functional improvement. For fitness professionals, understanding the underlying cause is paramount to crafting safe and effective exercise programs:

• Strength Training: Emphasize building strong muscles around hypermobile joints to provide dynamic stability. Focus on controlled, slow movements within a healthy range of motion.
• Proprioceptive Training: Exercises that challenge balance and body awareness can help improve joint position sense, reducing the risk of injury.
• Low-Impact Aerobics: Activities like swimming, cycling, or elliptical training are often preferred to minimize joint stress.
• Flexibility (Caution): While stretching might feel good, excessive or uncontrolled stretching can be detrimental, further destabilizing joints. Focus on maintaining functional flexibility rather than increasing range of motion.
• Avoid Hyperextension: Educate clients to be mindful of joint hyperextension during movements (e.g., locking out knees or elbows).
• Professional Guidance: Collaboration with physiotherapists, occupational therapists, and medical specialists is often necessary for comprehensive management.

Conclusion: A Complex, Multifaceted Condition

HMS/HSD is a complex, genetically determined condition rooted in the structural integrity of the body's connective tissues. The primary cause lies in inherited variations in genes responsible for proteins like collagen and elastin, leading to excessive joint laxity. Understanding this fundamental genetic predisposition is key to appreciating the wide array of symptoms experienced by individuals with HMS/HSD and for developing appropriate, evidence-based management and exercise strategies. For fitness educators and practitioners, recognizing the signs and understanding the mechanisms behind HMS/HSD allows for tailored, supportive, and safe interventions that prioritize joint stability and functional well-being.