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Early Peripheral Nerve Involvement at the Time of Coughing in Patients With RFC1 Intronic Expansion
Simon Frachet1, Pauline Chazelas1, Laurent Magy1
1From the Neurology Department (S.F., L.M.), University Hospital of Limoges; UR20218-NEURIT (S.F., P. Chazelas, L.M., A.-S.L.), University of Limoges; Biochemistry and Molecular Genetic Department (P. Chazelas, A.-S.L.), University Hospital of Limoges; Neurology Department (P. Cintas, P.G.); Department of Respiratory Medicine (D.B., L.G.), University Hospital of Toulouse; Neurology Department (L.E.), Cahors Hospital; and Department of Respiratory Medicine (B.M.), University Hospital of Limoges, France.
Objectives:
Cerebellar ataxia, neuropathy, and vestibular areflexia syndrome results from variations in RFC1 and is mostly caused by intronic biallelic pathogenic expansions (RE-RFC1). Refractory chronic cough (RCC) is frequently observed for years to decades preceding ataxia onset. Whether peripheral nerves are involved in the presymptomatic phase characterized by RCC is uncertain.
Methods:
Here, patients previously screened for RCC and identified as having at least one RE-RFC1 intronic expansion underwent a comprehensive clinical and neurophysiologic assessment and were screened for additional exonic variations.
Results:
Fourteen patients with RCC and RE-RFC1 were investigated. Seven patients presented with biallelic RE-RFC1 (Bi-RE-RFC1) while 7 presented with monoallelic RE-RFC1 (Mono-RE-RFC1). In patients with Mono-RE-RFC1, no additional exonic variation was identified, and clinical examinations were normal. Most of the patients with Bi-RE-RFC1 presented with subtle neurologic impairment, mainly exhibiting decreased lower limb vibration sense (85.7%). Nerve conduction studies revealed that all patients with Bi-RE-RFC1 exhibited lower sensory sum scores than patients with Mono-RE-RFC1 (median 20.2 µV vs 84.9 µV, p = 0.0012). In addition, the radial-to-sural sensory ratios were null or inverted (>0.5) in all patients but one with Bi-RE-RFC1, which is consistent with sensory neuronopathy.
Discussion:
Patients with Bi-RE-RFC1 already exhibit widespread sensory neuron involvement at the time of apparently isolated RCC.
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