The signs and symptoms of hereditary sensory neuropathy type 1 typically appear during a persons teens or twenties. While the features of this disorder tend to worsen over time, affected individuals have a normal life expectancy if signs and symptoms are properly treated. Type 1 is the most common form among the 5 types of HSAN. Its historical names include mal perforant du pied, ulcero-mutilating neuropathy, hereditary perforating ulcers, familial trophoneurosis, familial syringomyelia, hereditary sensory radicular neuropathy, among others. This type includes a popular disease Charcot-Marie-Tooth type 2B syndrome (HMSN 2B). that is also named as HSAN sub-type 1C. Type 1 is inherited as an autosomal dominant trait. The disease usually starts during early adolescence or adulthood. The disease is characterized by the loss of pain sensation mainly in the distal parts of the lower limbs; that is, in the parts of the legs farther away from the center of the body. Since the affected individuals cannot feel pain, minor injuries in this area may not be immediately recognized and may develop into extensive ulcerations. Once infection occurs, further complications such as progressive destruction of underlying bones may follow and may necessitate amputation. In rare cases, the disease is accompanied with nerve deafness and muscle wasting. Autonomic disturbance, if present, appears as anhidrosis, a sweating abnormality. Examinations of the nerve structure and function showed signs of neuronal degeneration such as a marked reduction in the number of myelinated fibers and axonal loss.
Supernumerary phantom limb is a condition where the affected individual believes and receives sensory information from limbs of the body that do not actually exist, and never have existed, in contradistinction to phantom limbs, which appear after an individual has had a limb removed from the body and still receives input from it. An fMRI study of a subject with a supernumerary phantom left arm was done by Khateb et al. at the Laboratory of Experimental Neuropsychology at the University of Geneva. When the subject was told to touch her right cheek with the phantom limb, there was increased activity in the motor cortex of her brain in the area roughly corresponding to the left arm. When she announced that she had touched the phantom limb to her cheek, activity was monitored in the area of the somatosensory cortex that corresponded to the right cheek. At times during the experiment, the subject was asked to move the phantom limb to a location that was obstructed or otherwise unfeasible. In these instances, there was similar activation of the motor cortex but no such activity in the somatosensory cortex. Affected areas of the brain
Motor cortex
Somatosensory cortex
Tactile (touch) controlling areas

See also
Body integrity identity disorder (BIID)
Supernumerary body part – having an extra limb

References

McGeoch, P.D. et al. (2009). Apotemnophilia – the neurological basis of a ‘psychological’ disorder. Nature Precedings DOI: 10101/npre.2009.2954.1.