SCN9A Variants May be Implicated in Neuropathic Pain Associated With Diabetic Peripheral Neuropathy and Pain Severity.

OBJECTIVES: Previous studies have established the role of SCN9A in various pain conditions, including idiopathic small fiber neuropathy. In the present study, we interrogate the relationship between common and rare variants in SCN9A gene and chronic neuropathic pain associated with diabetic peripheral neuropathy. DESIGN: Using a cohort of 938 patients of European ancestry with chronic neuropathic pain associated with diabetic peripheral neuropathy enrolled in 6 clinical studies and 2 controls (POPRES, n=2624 and Coriell, n=1029), we examined the relationship between SCN9A variants and neuropathic pain in a case-control study using a 2-stage design. The exonic regions of SCN9A were sequenced in a subset of 244 patients with neuropathic pain, and the variants discovered were compared with POPRES control (stage 1). The top associated variants were followed up by genotyping in the entire case collection and Coriell controls restricting the analysis to the matching patients from the United States and Canada only (stage 2). RESULTS: Seven variants were found to be associated with neuropathic pain at the sequencing stage. Four variants (Asp1908Gly, Val991Leu/Met932Leu, and an intronic variant rs74449889) were confirmed by genotyping to occur at a higher frequency in cases than controls (odds ratios ∼2.1 to 2.6, P=0.05 to 0.009). Val991Leu/Met932Leu was also associated with the severity of pain as measured by pain score Numeric Rating Scale (NRS-11, P=0.047). Val991Leu/Met932Leu variants were in complete linkage disequilibrium and previously shown to cause hyperexcitability in dorsal root ganglia neurons. CONCLUSIONS: The association of SCN9A variants with neuropathic pain and pain severity suggests a role of SCN9A in the disease etiology of neuropathic pain.