TRPA1 CHANNEL DYSFUNCTION IN PAINFUL SMALL FIBER NEUROPATHY

Small-fiber neuropathy (SFN) is a neurological disorder characterized by sensory alterations, pain, and autonomic dysfunction. Genetic screening of patients with idiopathic SFN has identified TRPA1 as a candidate gene due to its established role in pain and itch perception. In this study, we aimed to functionally characterize two TRPA1 genetic variants, p.Thr311Asn and p.Lys1046Glu, to establish genotype-phenotype correlations in patients with neuropathic pain. Mutant channels were expressed in HEK293T cells and compared with the wild-type (WT) hTRPA1. Channel function was assessed using whole-cell and single-channel patch clamp while calcium imaging was performed to evaluate channel activation. Additionally, TRPA1 sensitivity to agonists, particularly allyl isothiocyanate (AITC) and cinnamaldehyde (CA), was examined to further elucidate its role in pain signaling. Both mutant channels showed significant enhanced calcium responses when stimulated with AITC compared with WT. At the whole-cell level, p.Lys1046Glu variant presented increased basal current amplitudes compared to WT hTRPA1. Single-channel recordings revealed increased unitary conductance for both variants (234 pS for p.Lys1046Glu and 215 pS for p.Thr311Asn) compared with WT channels (169 pS). Furthermore, analysis of channel open probability (NPo) demonstrated higher values for the p.Lys1046Glu mutant (0.285) than for WT channels (0.076). Together, these findings suggest that both TRPA1 mutations exhibit a gain-of-function phenotype and are likely pathogenic, contributing to painful SFN development. Analysing the functional impact of SFN-associated TRPA1 variants and understanding the genetic basis of neuropathic pain is crucial for advancing its management to provide personalized treatment strategies to patients with painful SFN.