HSPG2 and Schwartz-Jampel syndrome: On the contrary, the importance of perlecan in neuromuscular junction (NMJ) formation associated with Wnt signaling [43], in the accumulation of acetylcholinesterase via collagen Q [44,45,46], and in promoting AChR clustering in the presence of laminin 2 [47] suggested that myotonia in SJS might be caused by the dysfunction of NMJ.