11 experts from France, Germany, Turkey, Sweden and the Netherlands, met in Naarden on December 14-15 under the auspices of ENMC to review advances and knowledge in an extremely rare neuromuscular condition called Schwartz-Jampel syndrome (SJS). The classical form of SJS is caused by mutations in a gene encoding a large protein calledperlecan which is located just outside the muscle cell. This protein is a major component of the extracellular matrix.
The SJS is a hereditary disorder characterised by severe and permanent myotonia and skeletal malformations.
Interestingly, the same protein has been found mutated in a totally different disease with bone malformations (DDSH, dyssegmental dysplasia of the Silverman Handmaker type).
A neonatal form of SJS (also known as SJS2) has been reported by some authors and shares clinical and radiological similarities with a bone disorder called Stuve-Wiedemann syndrome. We now have evidence that the two latter disorders are likely to be caused by mutations in a gene which is distinct from the perlecan gene itself.
In view of these new genetic findings, diagnostic criteria of the SJS have been revised.
An animal model lacking perlecan has been extensively studied and ressembles DDSH. The various interactions of perlecan have been reviewed as well the potential mechanisms causing myotonia. Other pathogenetic avenues have been explored such as the potential implication of the neuromuscular junction in myotonia.
An international consortium has been established and stresses the need for collecting more families or cases with these rare conditions, to obtain additional biological samples such as skin and muscle biopsies.
Knowledge of the pathogenesis should benefit from the development of cellular or animal models as well as optimal interaction between clinical and basic scientists.
An extended report of this meeting is published in Neuromuscular Disorders, Volume 13, No. 4, May 2003.
Prof. B. Fontaine (Paris, France)
Prof. H. Topaloglu (Ankara, Turkey)
Dr. S. Nicole (Paris, France)