NGF and hereditary sensory and autonomic neuropathy type 4: Therelationship between NGF and pain is supported by genetic evidence: mutations inthe NGF TrkA receptor in patients affected by an hereditary rare disease(Hereditary Sensory and Autonomic Neuropathy type IV, HSAN IV) determine acongenital form of severe pain insensitivity, with mental retardation, while amutation in NGFB gene, leading to the aminoacid substitutionR100W in mature NGF, determines a similar loss of painperception, without overt cognitive neurological defects (HSAN V).