Interestingly, intramuscular injections of NGF are able to induce neuronal sensitization in rats (Hoheisel et al., 2007) and some mutations in TrkA result in congenital insensitivity to pain with anhidrosis (CIPA), an autosomal recessive disorder characterized by the inability to feel pain and absence of sweating (Indo et al., 1996). The gene discussed is NGF; the disease is hereditary sensory and autonomic neuropathy type 4.