Interestingly, in congenital insensitivity to pain with anhidrosis (hereditary sensory and autonomic neuropathy 4, HSAN4), mutations in tyrosine receptor kinase A (TrkA), the receptor for nerve growth factor (NGF), result in subjects presenting with a total loss of C-fibers and lack of nociception, and they do not sweat due to hypotrophic, uninnervated sweat glands (Indo,2009). This evidence concerns the gene NTRK1 and anhidrosis.