Targeted neurological screening for RFC1-related disease in unexplained chronic cough
Vicente Gajate-García1, María Fenollar-Cortés2, Juan Luis Rodríguez-Hermosa3,4,5
1Neuromuscular Diseases Unit, Department of Neurology, Hospital Clínico San Carlos, Instituto de Investigación Sanitaria del Hospital Clínico San Carlos (IdISSC), Calle Profesor Martín Lagos s/n, 28040, Madrid, Spain.
Background:
Cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS) is caused by biallelic pathogenic repeat expansions in the RFC1 gene. Chronic cough can precede the neurological features of CANVAS by decades and, in some instances, may be the sole clinical manifestation. However, the prevalence of biallelic RFC1 repeat expansions among patients with unexplained chronic cough (UCC), as well as the diagnostic utility of targeted neurological screening in this setting, remains unclear.
Methods:
In this 6-month pilot study, 13 consecutive patients with UCC underwent a standardized neurological evaluation and screening nerve conduction studies (NCS) during a single clinical visit. All patients were subsequently tested for RFC1 repeat expansions. Those carrying biallelic pathogenic expansions (RFC1+) were further assessed with extended NCS, electrochemical skin conductance (ESC), and thermal quantitative sensory testing (QST).
Results:
Three patients (23%) were RFC1+. Clinical and demographic features did not significantly differ between RFC1+ and RFC1- groups. All RFC1+ individuals exhibited marked bilateral reduction in radial and sural sensory nerve action potential (SNAP) amplitudes. In contrast, only two RFC1- patients showed reduced sural SNAPs. QST revealed impaired cold detection thresholds with preserved warm detection in all RFC1+ cases, while ESC results were normal.
Conclusions:
These findings suggest that standardized neurological and electrophysiological assessment can detect subclinical sensory neuropathy in UCC patients lacking overt neurological symptoms, thereby identifying those more likely to carry RFC1 expansions. The observed 23% prevalence supports incorporating RFC1 testing into the diagnostic approach for selected UCC patients, particularly when radial SNAP amplitudes are reduced.
