Hereditary sensory neuropathies

Hereditary sensory neuropathies (HSNs) are a group of genetically determined peripheral neuropathies with prominent disturbance of the peripheral sensory neurons. They are characterized by sensory loss, insensitivity to pain, a variable degree of muscle weakness and wasting, as well as autonomic features. Frequent complications are foot ulcerations and infections that may lead to osteomyelitis, followed by necrosis and amputations. Consequently, the hereditary sensory neuropathies have also been termed ulceromutilating neuropathies. On the other hand, in the presence of additional motor weakness, they have been subclassified among the group of Charcot-Marie-Tooth (CMT) disorders. Sporadic and familial cases with different modes of inheritance are known to affect both children and adults. The most prevalent forms of the autosomal dominantly inherited hereditary sensory neuropathies are HSN I and CMT 2b. HSN I is associated with mutations in the SPTLC1 gene, whereas mutations in the RAB7 gene have been identified in CMT 2b. However, at least one more hitherto unknown gene responsible for autosomal-dominant hereditary sensory neuropathies must exist. Autosomal-recessive hereditary sensory neuropathies types III and IV, and probably also type V, result from mutations in the IKBKAP and NTRK1 genes. Very recently, the gene in HSN II (HSN2) has been identified. A spontaneous autosomal-recessive mutation in the Cct4 gene has been reported in the Sprague-Dawley rat strain with early onset sensory neuropathy. Although no curative treatment is available so far, and current therapy is limited to symptom relief, these molecular genetic advances in knowledge about the hereditary sensory neuropathies can be translated into clinical practice by improving diagnosis and genetic counseling. They will also be the basis for functional studies in the future.