STKE Schwann cells of the peripheral nervous system express periaxin, a cytosolic protein that contains a PDZ domain, a hallmark of adaptor proteins that assemble macromolecular signaling complexes. Mutations in the human periaxin gene cause the demyelinating neuropathy of Charcot-Marie-Tooth disease, and mice that lack functional periaxin develop a similar condition. Sherman et al. show that periaxin associates with a cytoplasmic protein, dystrophin-related protein 2, which binds to dystroglycan, the cell surface receptor for extracellular matrix molecules. Periaxin forms PDZ domain-mediated dimers and hence clusters the associated dystrophin-glycoprotein complexes at the surface of Schwann cells. Disruption of this clustering destroys dystroglycan organization, thus affecting neuron-Schwann cell interaction and myelin sheath integrity. — LDC Neuron 30 , 677 (2001).