Rare Nav1.7 variants associated with painful diabetic peripheral neuropathy
Diabetic peripheral neuropathy (DPN) is a common disabling complication of diabetes. Almost half of DPN patients develop neuropathic pain for which current analgesic treatments are inadequate. Understanding the role of genetic variability in the development of painful DPN is needed for improved understanding of pain pathogenesis, for better patient stratification in clinical trials and to target therapy more appropriately. Here we examined the relationship between variants in the voltage gated sodium channel Nav1.7 and neuropathic pain in a deeply phenotyped cohort of patients with DPN. While no rare variants were found in 78 participants with painless DPN, we identified twelve rare Nav1.7 variants in ten (out of 111) study participants with painful DPN. Five of these variants had previously been described in the context of other neuropathic pain disorders and seven have not previously been linked to neuropathic pain. Those patients with rare variants reported more severe pain and greater sensitivity to pressure stimuli on quantitative sensory testing. Electrophysiological characterization of two of the novel variants (M1852T and T1596I) demonstrated gain of function changes as a consequence of markedly impaired channel fast inactivation. By using a structural model of Nav1.7 we were also able provide further insight into the structural mechanisms underlying fast activation and the role of the C-terminal domain in this process. Our observations suggest that rare Nav1.7 variants contribute to the development neuropathic pain in patients with diabetic peripheral neuropathy. Their identification should aid understanding of sensory phenotype, patient stratification and help target treatments effectively.