Natural History and Treatment of Peripheral Inherited Neuropathies

Abstract

Charcot-Marie-Tooth disease (CMT) is genetically highly heterogeneous. Disease course and severity vary according to CMT type, causative gene, and mutation type, but considerable phenotypic variability may occur also for the same CMT type. Research is focused on possible modifier factors particularly in CMT1A associated with Peripheral Myelin Protein 22 (PMP22) overexpression. Natural history studies are important to define disease course in different CMT types and to allow better assessment of intervention efficacy. Only a few such studies have been carried out, mainly on CMT1A, and described impairment and disability progression. Motor potential amplitudes seem to correlate with disease severity and progression, suggesting that axonal loss is the basis of disability in CMT. There is need to develop suitable and reproducible outcome measures: the CMT Neuropathy Score is the only validated outcome score specific for CMT, but others have been tested during the last few years. Currently there is no effective drug therapy for CMT and supportive treatment is limited to physical therapy, orthotics, surgical treatment of skeletal deformities and soft tissue abnormalities, and symptomatic drug treatment. Research is focused on developing new treatment strategies and approaches. The progesterone antagonist onapristone proved to be effective in a rat model of CMT1A; unfortunately, currently available progesterone antagonists are too toxic to be safely administered to patients. Neurotrophin-3 (NT3), a neurotrophic factor known to promote axonal growth, was tested with favourable results in two animal models and in a pilot study involving eight CMT1A patients. Ascorbic acid (AA) administration to CMT1A mice improved clinical and neuropathological findings, possibly by down-regulating PMP22 through a cAMP mediated mechanism. Clinical trials of AA in the human disease are currently being performed. Curcumin stimulates translocation of misfolded protein from the endoplasmic reticulum and proved useful for selected myelin protein zero and PMP22 mutants in vitro and in the animal models Trembler and TremblerJ.