Schwartz-Jampel syndrome

Schwartz-Jampel syndrome (SJS), also known as chondrodystrophic myotonia or myotonic chondrodystrophy, is a rare inherited disorder characterized by the combination of permanent muscle stiffness (myotonia) and skeletal abnormalities (chondrodysplasia). The condition is caused by mutations in the HSPG2 gene, which encodes perlecan, a large proteoglycan found in basement membranes and cartilage. Perlecan deficiency disrupts normal skeletal development and neuromuscular function, leading to the characteristic features of the disease. The hallmark clinical features include continuous muscle stiffness and contractures, a distinctive facial appearance with a fixed facial expression, blepharospasm (involuntary eyelid closure), pursed lips, and a small jaw (micrognathia). Skeletal abnormalities are prominent and include short stature, bowing of long bones, joint contractures, kyphoscoliosis, hip dysplasia, and platyspondyly (flattened vertebral bodies). Affected individuals typically have a characteristic high-pitched voice and may experience feeding difficulties in infancy. The myotonia in SJS is distinct from classical myotonia and is thought to result from continuous muscle fiber activity rather than a primary ion channel defect. Two clinical subtypes have been described: Type 1 (the classic and more common form) presents in childhood with moderate skeletal changes and is compatible with a normal lifespan, while Type 2 (also called Stüve-Wiedemann syndrome, now recognized as a separate entity) is a more severe neonatal form. Treatment is primarily symptomatic and supportive. Muscle stiffness may be managed with medications such as carbamazepine or other membrane-stabilizing agents. Orthopedic interventions may be needed for skeletal complications, and surgical correction of blepharospasm with botulinum toxin injections can improve vision and quality of life. Physical therapy is important for maintaining mobility and preventing further contractures.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

Common questions about Schwartz-Jampel syndrome