Peripheral nerve demyelination caused by a mutant Rho GTPase guanine nucleotide exchange factor, frabin/FGD4

GTPases of the Rho subfamily are widely involved in the myelination of the vertebrate nervous system. Rho GTPase activity is temporally and spatially regulated by a set of specific guanine nucleotide exchange factors (GEFs). Here, we report that disruption of frabin/ FGD4, a GEF for the Rho GTPase cell- division cycle 42 (Cdc42), causes peripheral nerve demyelination in patients with autosomal recessive Charcot-Marie-Tooth ( CMT) neuropathy. These data, together with the ability of frabin to induce Cdc42- mediated cell-shape changes in transfected Schwann cells, suggest that Rho GTPase signaling is essential for proper myelination of the peripheral nervous system.