Definition:

Congenital insensitivity to pain (CIP) is condition affecting pain sensation and olfaction. A loss-of-function of the SCN9A, the gene encoding Nav1.7, can produce CIP. Patients with Nav1.7-related CIP present with a history of not ever experiencing any pain even after burns, bone fractures, lip- and tongue-biting, and they do not experience visceral pain. Additionally, patients with Nav1.7-related CIP do not show apparent sympathetic dysfunction and have a normal axon reflex response to histamine. Homozygous and compound null mutations in SCN9A are predicted to truncate the channel protein, resulting in loss-of-function mutations in Nav1.7 and the complete loss of Nav1.7 current in all of the neurons in which this channel is expressed. Marsili syndrome(MARSIS) is an autosomal dominant congenital insensitivity to pain, caused by mutations in ZFHX2 gene.