Electrophysiological studies in a mouse model of Schwartz-Jampel syndrome demonstrate muscle fiber hyperactivity of peripheral nerve origin.
Schwartz-Jampel syndrome (SJS) is an autosomal-recessive condition characterized by muscle stiffness and chondrodysplasia. It is due to loss-of-function hypomorphic mutations in the HSPG2 gene that encodes for perlecan, a proteoglycan secreted into the basement membrane. The origin of muscle stiffness in SJS is debated. To resolve this issue, we performed an electrophysiological investigation of an SJS mouse model with a missense mutation in the HSPG2 gene. Compound muscle action potential amplitudes, distal motor latencies, repetitive nerve stimulation tests, and sensory nerve conduction velocities of SJS mice were normal. On electromyography (EMG), neuromyotonic discharges, that is, bursts of motor unit action potentials firing at high rates (120-300 HZ), were constantly observed in SJS mice in all muscles, except in the diaphragm. Neuromyotonic discharges were not influenced by general anesthesia and disappeared with curare administration. They persisted after complete motor nerve section, terminating only with Wallerian degeneration. These results demonstrate that perlecan deficiency in SJS provokes a neuromyotonic syndrome. The findings further suggest a distal axonal localization of the generator of neuromyotonic discharges. SJS should now be considered as an inherited disorder with peripheral nerve hyperexcitability.
Echaniz-Laguna
Andoni
A
Département de Neurologie, Hôpital Civil de Strasbourg, 1 Place de l'Hôpital, BP426, 67091 Strasbourg,France. echaniz-laguna@medecine.u-strasbg.fr
Rene
Frédérique
F
Marcel
Christophe
C
Bangratz
Marie
M
Fontaine
Bertrand
B
Loeffler
Jean-Philippe
JP
Nicole
Sophie
S
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D055592:Biophysical Phenomena; D003472:Curare / Q000494:pharmacology; D004195:Disease Models, Animal; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019812:Heparan Sulfate Proteoglycans / Q000172:deficiency / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D020125:Mutation, Missense / Q000235:genetics; D009431:Neural Conduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology; D010009:Osteochondrodysplasias / Q000235:genetics / Q000473:pathology* / Q000503:physiopathology*; D010525:Peripheral Nerves / Q000503:physiopathology*; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology
D019812:Heparan Sulfate Proteoglycans; D003473:Neuromuscular Nondepolarizing Agents; C071927:perlecan; D003472:Curare