SCN9A-related disorder is a difficult diagnosis to consider, and to make in a young child – although now with gene testing this is easier. Most individuals do not get a diagnosis until they are 5-8 years old. The diagnosis has been used as a defence in child physical abuse cases, and clinical and molecular testing quickly clarifies the situation. Whilst child abuse is common and congenital insensitivity to pain very rare, many children with the diagnosis were removed from their parents temporarily until the diagnosis became clear.
Individuals with Nav1.7 (the sodium ion channel that is encoded by the SCN9A gene) congenital pain insensitivity have a complete inability to experience pain and are also anosmic. The disorder is congenital and often presents in early childhood through biting of the lips, tongue and fingers or by parents observing painless immunisations. With the exception of pain sensation, somatosensory functions are normal with touch, warm and cold temperatures, proprioception, tickle and pressure perception. Patients have normal intelligence, normal motor development and show no symptoms of autonomic nervous system dysfunction. Multiple burns, bruises, cuts and bone fractures are frequently reported. Visceral pains are not perceived, including painless labour, although a form of neuropathic pain has been reported in a patient following injuries sustained during painless childbirth. Nav1.7 congenital pain insensitivity is still a relatively rare disorder. Patients have been identified with this disorder from multiple human populations.
Nerve and skin biopsies in Nav1.7-pain insensitive patients typically show structurally normal sensory nerves – therefore nerve biopsy should not be necessary to make this diagnosis. However, a small subgroup of patients have been described where morphological abnormalities of sensory nerves have been identified and these patients are classified as having hereditary and sensory autonomic neuropathy (HSAN) type IID.