[Motor Neuron Involvement in RFC1 CANVAS/Spectrum Disorders].

Cerebellar ataxia with neuropathy and vestibular areflexia syndrome (CANVAS) is characterized by the triad of cerebellar ataxia, bilateral vestibular impairment, and sensory neuropathy. The responsible anatomical region for the sensory disturbance in CANVAS is reportedly the dorsal root ganglion, which suggests neuronopathy rather than neuropathy as the pathomechanism of this peripheral nervous system disorder. Early on, motor neuron involvement was considered rare in CANVAS. The etiology of CANVAS includes the homozygous pentanucleotide repeat expansion within the RFC1 gene, resulting in diverse phenotypes and motor deficits such as brisk reflex, extensor plantar responses, or spasticity of the upper motor neurons and muscle wasting, weakness, cramp, or fasciculation of the lower motor neurons. CANVAS patients with AAGGG repeat expansions may show motor neuron involvement, with considerable variation in the reported frequencies. In contrast, although some patients with ACAGG repeat expansions also show motor neuron involvement, its frequency remains elusive.