Schwartz-Jampel syndrome and perlecan deficiency.

Schwartz-Jampel syndrome (SJS) is a rare autosomal recessive disorder characterized by the association of myotonia with chondrodysplasia. A positional cloning strategy allowed the localization and the identification of perlecan as the disease causing gene. Another human recessive disorder, the Dyssegmental Dysplasia, Silverman-Handmaker type (DDSH), is caused by functional null mutations of the perlecan gene. A gene-dosage effect seems to account for the correlation between the phenotype and the mutations within the gene: SJS would be associated with hypomorph mutations of the perlecan gene and DDSH would be due to the absence of functional perlecan. Perlecan is the major heparan sulfate proteoglycan of extracellular matrix and basement membranes that displays various functions. Based on these functions, several hypotheses are evoked to explain chondrodysplasia and the unusual myotonia in SJS. Mouse models are invaluable tools to explore these hypotheses. Since knock-out mice develop a phenotype similar to DDSH, we have developed a SJS mouse model by reproducing the hypomorph effect of SJS perlecan mutation in this species. The characterization of this mouse model will help to understand the pathophysiological mechanism leading to this multisystemic human disorder.