Electrophysiological contribution to understanding the pathophysiology of Friedreich's ataxia

Friedreich's ataxia (FA) is the most frequent early onset recessive ataxia. Ataxia clinical progression is slow, but the majority of patients is wheelchair-bound before 30 years of age. Some studies suggested that the peripheral sensory neuropathy was a dynamic process that could explain the clinical worsening. In 1983 an electrophysiological and histological study showed peripheral nerve axonal degeneration unrelated to disease duration or severity. A follow-up study confirmed that symptom progression is independent from peripheral neuropathy that is not progressive. A defective development of the largest neurons of the dorsal ganglion was supposed. When the unstable GAA expansion in the X25 gene was identified as the responsible mutation in the majority of FA patients, genotype-phenotype correlation studies were performed. A direct correlation between GAA expansion and involvement of peripheral nerve sensory fibers and central somatosensory pathway was shown. Disease duration correlates with pyramidal, auditory and visual pathway involvement, while the GAA expansion size has no effect.