A much smaller number of people are insensitive to <answer>pain</answer> due to an inborn abnormality of the nervous system, known as "congenital insensitivity to <answer>pain</answer>". Children with this condition incur carelessly-repeated damage to their tongues, eyes, joints, skin, and muscles. Some die before adulthood, and others have a reduced life expectancy.[citation needed] Most people with congenital insensitivity to <answer>pain</answer> have one of five hereditary sensory and autonomic neuropathies (which includes familial dysautonomia and congenital insensitivity to <answer>pain</answer> with anhidrosis). These conditions feature decreased sensitivity to <answer>pain</answer> together with other neurological abnormalities, particularly of the autonomic nervous system. A very rare syndrome with isolated congenital insensitivity to <answer>pain</answer> has been linked with mutations in the SCN9A gene, which codes for a sodium channel (Nav1.7) necessary in conducting <answer>pain</answer> nerve stimuli.
An abnormality of the nervous system can render a small number of people insensitive to what?
pain