Résumé
Schwartz–Jampel syndrome (SJS) (OMIM 255800) and dyssegmental dysplasia, Silverman–Handmaker type (DDSH) (OMIM 224410), are two infrequent human disorders transmitted with an autosomal-recessive mode of inheritance. Both are characterized by abnormal endochondral ossification resulting in skeletal malformations. However, they differ on their degree of severity; DDSH is lethal, unlike SJS. In addition, SJS is characterized by a permanent muscle stiffness (myotonia) owing to a severe muscle hyperexcitability, which has not been reported in DDSH. Both disorders have been linked to loss of function mutations in the gene encoding perlecan, the major heparan sulfate (HS) proteoglycan (HSPG) of basement membranes (BMs) (see Chapter 163). The functions of perlecan have been in part elucidated, and animal models with perlecan deficiency are available, which suggest SJS and DDSH pathophysiological models.