Hereditary sensory and autonomic neuropathy

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Hereditary sensory and autonomic neuropathy (HSAN) or hereditary sensory neuropathy (HSN) is a condition used to describe any of the types of this disease which inhibit sensation.

They are less common than Charcot-Marie-Tooth disease.

Five different clinical entities have been described under hereditary sensory and autonomic neuropathies – all characterized by progressive loss of function that predominantly affects the peripheral sensory nerves. Their incidence has been estimated to be about 1 in 25,000.

Hereditary sensory neuropathy type 1 is a condition characterized by nerve abnormalities in the legs and feet (peripheral neuropathy). Many people with this condition have tingling, weakness, and a reduced ability to feel pain and sense hot and cold. Some affected individuals do not lose sensation, but instead feel shooting pains in their legs and feet. As the disorder progresses, the sensory abnormalities can affect the hands, arms, shoulders, and abdomen. Affected individuals may also experience muscle wasting and weakness as they get older, but this varies widely within families.

Affected individuals typically get open sores (ulcers) on their feet or hands or infections of the soft tissue of the fingertips (whitlows) that are slow to heal. Because affected individuals cannot feel the pain of these sores, they may not seek treatment right away. Without treatment, the ulcers can become infected and may require amputation of the surrounding area.

Rarely, people with hereditary sensory neuropathy type 1 will develop hearing loss caused by abnormalities of the inner ear (sensorineural hearing loss).

The signs and symptoms of hereditary sensory neuropathy type 1 typically appear during a person's 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 such as feet and lower legs. Since the affected individuals cannot feel pain, minor injuries in the painless 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 case, 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. Sensory neurons lose the ability to transmit signals, while motor neurons has reduced ability to transmit signals.