In the mouse model of Charcot–Marie Tooth neuropathy, the ERK signaling pathway was activated within the nuclei of certain myelinating Schwann cells, which is directly related to elevated levels of the macrophage-attracting cytokine MCP-1 in the nerves, identifying ERK signaling pathway as a crucial intracellular pathway linking the Schwann cell mutations to the activation of macrophages that are pathogenetically significant in the peripheral nerves (Fischer et al., 2008). The gene discussed is CCL2; the disease is Charcot-Marie-Tooth disease, axonal, type 2FF.