Chapter 120 - Autonomic and Sensory Disorders

Abstract

The complexities of the autonomic nervous system (ANS) and its intimate relationship with sensory function are especially well illustrated in the group of genetic disorders known as hereditary sensory and autonomic neuropathies (HSAN). Each HSAN disorder is caused by a different genetic error affecting a specific aspect of small fiber development and/or maintenance resulting in variable phenotypic expression. With the exception of HSAN type I, which is a dominant disorder presenting in the second decade, the other HSAN are autosomal recessive disorders whose mutations impede normal neural crest migration and differentiation and result in decreased neuronal populations. Therefore signs are usually present within the first year of life. For each HSAN type, penetrance is complete but there can be marked variability in expression. Decreased analgesia is characteristic of all HSANs, whereas the degree and type of autonomic dysfunction differs among the HSANs.