Schwartz–Jampel Syndrome (SJS) is a rare autosomal recessive disorder characterized by a combination of musculoskeletal abnormalities and continuous muscle contractions.

Clinical Features:

1. Musculoskeletal Features:

   • Chondrodysplasia: Abnormal cartilage development leads to short stature and joint contractures.
   • Facial Features:
     • Blepharophimosis: Narrowing of the eye openings.
     • Pursing of the mouth and puckering of the chin due to persistent muscle contraction.
   • Stiffness: Muscle stiffness affecting the limbs, often worsened with cold or exertion.

2. Muscle Abnormalities:

   • Continuous muscle contraction, even at rest, contributes to stiffness and abnormal posture.
   • Despite the muscle contraction, serum creatine kinase (CK) levels are normal or mildly elevated.

3. Electromyography (EMG):

   • Abnormal, continuous muscle fiber activity is seen, even in the absence of voluntary movement.

4. Histological Findings:

   • Muscle biopsy typically appears normal or shows nonspecific changes.

Genetics:

• Caused by recessive mutations in the HSPG2 gene, which encodes perlecan:
  • A heparan sulfate proteoglycan found in basement membranes and cartilage.
  • Perlecan is critical for maintaining the structural integrity of cartilage and other connective tissues.

Diagnosis:

1. Clinical Diagnosis:

   • Based on characteristic features such as short stature, facial dysmorphisms, and muscle stiffness.

2. Genetic Testing:

   • Confirms mutations in the HSPG2 gene.

3. Differential Diagnosis:

   • Conditions such as hyperekplexia, other congenital myopathies, and disorders affecting cartilage and muscle should be ruled out.

Treatment:

1. Symptomatic Management:

   • Sodium channel blockers (e.g., phenytoin) may help reduce continuous muscle contractions.
   • Benzodiazepines can be used for symptomatic relief of stiffness.

2. Supportive Therapies:

   • Physical therapy to maintain joint mobility and reduce contractures.
   • Orthopedic interventions for severe joint or skeletal deformities.

3. Prognosis:

   • With appropriate management, many individuals can achieve good functional outcomes. However, symptoms are chronic and may require lifelong management.