Background & Aims

Approximately 10% of the world population is affected by neuropathic pain, suffering from both impaired life quality as well as reduced working capacity (1). Associated diseases may include impairment of small caliber nerve fibers, i.e., thinly myelinated A-delta and unmyelinated C-fibers. These small fiber neuropathies (SFN) result in acral burning pain but the exact pathomechanism remains unclear (2,3). Involvement of pain-associated gene variants are gaining attention and may help to explain the often severe pain in hereditary SFN. Respective variants reported so far were frequently associated with genes encoding for voltage-gated sodium channels (NaV) (4,5). We aim to determine the pathogenic significance of a previously undescribed variant of the gene SCN10A, T365N, encoding Nav1.8. This variant was detected in one index patient and three out of four siblings with significantly differing pain phenotypes. Our question is whether variant T365N is causative for the present SFN.

Methods

We recruited four siblings carrying the NaV1.8 variant T365N as well as one healthy control subject (ctrl). Detailed medical history reports and questionnaires were taken. Neurological examinations including electroneurography and small fiber testing (QST, PREP, CCM and skin punch biopsies) were performed. Patients’ pain phenotypes were: permanent generalized pain (pat. 1, index patient), generalized pain attacks (pat. 2), no pain (pat. 3), and permanent facial pain (pat. 4).

Patient’s fibroblasts obtained by skin punch biopsy were reprogrammed into induced pluripotent stem cells (iPSC). iPSC were then differentiated into iSN using a small-molecule based protocol (6). Whole-cell patch-clamp recordings were analyzed based on parameters like amplitude, firing frequency, half-width, rheobase, and threshold potential of action potentials to investigate neuronal functionality. NaV1.8 gene expression was determined in iPSC and iSN using qPCR and compared between the T365N variant and ctrl.

Results

Clinical phenotypes presented rather differently between patients carrying T365N spanning a spectrum from focal episodic pain in the face to generalized permanent pain. In vitro data showed that rheobase and threshold difference of pat. 2 was increased in comparison to ctrl (p<0.01) while threshold potential of pat. 1 was elevated compared to ctrl (p<0.01). Halftime was higher in iSN of pat. 3compared to ctrl (p<0.05). No changes in membrane potential, hyperpolarization, amplitude, and firing rate could be observed in comparison to ctrl. NaV1.8 gene expression was elevated in iSN compared to iPSC of all subjects but no difference between T365N and ctrl was detected.

Conclusions

Despite parallels in the areas of paresthesia and influencing factors, patients with T356N primarily show different symptom manifestations and degrees of pain severity. A clear genotype-phenotype correlation is therefore not yet possible. Nevertheless, the involvement of multifactorial influences and a wide distribution of pain indicate a potential genetic SFN. The in vitro data available to date show individual changes in the electrophysiological properties of the patients’ sensory neurons. As the NaV1.8 variant T365 does not affect channel expression on RNA level in iSN, our data point towards a functional impairment. Further investigations of sodium currents in transfected rodent cell lines will follow to understand the relevance of NaV1.8 variant T365N in pain syndromes.

References

1.van Hecke O, Austin SK, Khan RA, Smith BH, Torrance N. Neuropathic pain in the general population: a systematic review of epidemiological studies. Pain. 2014;155(4):654-62.
2.Sommer C, Uceyler N. [Not Available]. Fortschr Neurol Psychiatr. 2018;86(8):509-18.
3.Finsterer J, Scorza FA. Small fiber neuropathy. Acta Neurol Scand. 2022;145(5):493-503.
4.Hoeijmakers JG, Faber CG, Merkies IS, Waxman SG. Painful peripheral neuropathy and sodium channel mutations. Neurosci Lett. 2015;596:51-9.
5.de Greef BTA, Hoeijmakers JGJ, Gorissen-Brouwers CML, Geerts M, Faber CG, Merkies ISJ. Associated conditions in small fiber neuropathy – a large cohort study and review of the literature. Eur J Neurol. 2018;25(2):348-55.
6.Klein T, Grüner J, Breyer M, Schlegel J, Schottmann NM, Hofmann L, et al. Small fibre neuropathy in Fabry disease: a human-derived neuronal in vitro disease model. bioRxiv. 2023:2023.08.09.552621.

Presenting Author

Nicole Michelle Schottmann

Poster Authors

Nicole Schottmann

MSc

University Hospital of Würzburg

Lead Author

E-mail

Caren Meyer zur Altenschildesche

University Hospital of Wuerzburg

Lead Author

Julia Grüner

University Hospital of Wuerzburg

Lead Author

E-mail

Bettina Vignolo

M.Sc.

University Hospital of Wuerzburg

Lead Author

E-mail

Nurcan Üçeyler

MD

Department of Neurology, University of Würzburg, Germany

Lead Author

E-mail

Topics

  • Specific Pain Conditions/Pain in Specific Populations: Neuropathic Pain - Peripheral