Hereditary sensory and autonomic neuropathy, type 2 (HSAN2) is an inherited disorder characterized by profound and universal sensory loss involving large and small fiber nerves, and marked hypotonia. The exact prevalence is unknown, but is estimated as very low (less than 50 cases reported). HSAN2 presents in infancy or early childhood and is non-progressive. There is no sex preference or particular ethnic preponderance, and to date there is no increased incidence of consanguinity.
Initial symptoms (from birth to 3 years) include severe swallowing and feeding problems, frequent apnea, self-mutilation, and delayed development. Gastroesophageal reflux is common. Sensory dysfunction is manifested by absent pain perception, severely decreased temperature perception, and depressed deep tendon reflexes (with no muscle atrophy or muscle weakness). Position sense, taste sensation, and corneal and gag reflexes may be diminished. Vibration sense may be normal. Trophic changes are present in the upper and lower extremities. HSAN2 is associated with frequent occurrence of unrecognized injuries and fractures of hands, feet, and limbs, as well as Charcot joints. Hearing loss is reported in about 30% of patients and postural hypotention in about 25% of patients. Pupils have an exaggerated response to parasympathomimetic agents; overflow tearing is frequently delayed. Hyperhydrosis and patchy areas of anhidrosis occur occasionally. Absent axon flare (following intradermal histamine) and lack of fungiform papilla on the tongue are characteristic features of HSAN2.