Multisystemic RFC1-Related Disorder: Expanding the Phenotype Beyond Cerebellar Ataxia, Neuropathy, and Vestibular Areflexia Syndrome.

Background and Objectives: The RFC1 spectrum has become considerably expanded as multisystemic features beyond the triad of cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS) have started to be unveiled, although many still require clinical replication. Here, we aimed to clinically characterize a cohort of RFC1-positive patients by addressing both classic and multisystemic features. In a second part of this study, we prospectively assessed small nerve fibers (SNF) and autonomic function in a subset of these RFC1-related patients. Methods: We retrospectively enrolled 67 RFC1-positive patients from multiple neurologic centers in Portugal. All patients underwent full neurologic and vestibular evaluation, as well as neuroimaging and neurophysiologic studies. For SNF and autonomic testing (n = 15), we performed skin biopsies, quantitative sensory testing, sudoscan, sympathetic skin response, heart rate deep breathing, and tilt test. Results: Multisystemic features beyond CANVAS were present in 82% of the patients, mainly chronic cough (66%) and dysautonomia (43%). Other features included motor neuron (MN) affection and motor neuropathy (18%), hyperkinetic movement disorders (16%), sleep apnea (6%), REM and non-REM sleep disorders (5%), and cranial neuropathy (5%). Ten patients reported an inverse association between cough and ataxia severity. A very severe epidermal denervation was found in skin biopsies of all patients. Autonomic dysfunction comprised cardiovascular (67%), cardiovagal (54%), and/or sudomotor (50%) systems. Discussion: The presence of MN involvement, motor neuropathy, small fiber neuropathy, or extrapyramidal signs should not preclude RFC1 testing in cases of sensory neuronopathy. Indeed, the RFC1 spectrum can overlap not only with multiple system atrophy but also with hereditary motor and sensory neuropathy, hereditary sensory and autonomic neuropathy, and feeding dystonia phenotypes. Some clinical-paraclinical dissociations can pose diagnostic challenges, namely large and small fiber neuropathy and sudomotor dysfunction which are usually subclinical.

Sarcomeric disorganization and nemaline bodies in muscle biopsies of patients with EXOSC3-related type 1 pontocerebellar hypoplasia.

INTRODUCTION: Mutations in the EXOSC3 gene are responsible for type 1 pontocerebellar hypoplasia, an autosomal recessive congenital disorder characterized by cerebellar atrophy, developmental delay, and anterior horn motor neuron degeneration. Muscle biopsies of these patients often show characteristics resembling classic spinal muscle atrophy, but to date, no distinct features have been identified. METHODS: Clinical data and muscle biopsy findings of 3 unrelated patients with EXOSC3 mutations are described. RESULTS: All patients presented as a severe congenital cognitive and neuromuscular phenotype with short survival, harboring the same point mutation (c.92G>C; p.Gly31Ala). Muscle biopsies consistently showed variable degrees of sarcomeric disorganization with myofibrillar remnants, Z-line thickening, and small nemaline bodies. CONCLUSIONS: In this uniform genetic cohort of patients with EXOSC3 mutations, sarcomeric disruption and rod structures were prominent features of muscle biopsies. In the context of neonatal hypotonia, ultrastructural studies might provide early clues for the diagnosis of EXOSC3-related pontocerebellar hypoplasia. Muscle Nerve 59:137-141, 2019.