SCN9A and peripheral neuropathy: Variants in SCN9A that encode the voltage-gated sodium channel Nav1.7 have previously been linked to multiple pain disorders, including the Mendelian extreme pain disorders IEM73 and PEPD21 as well as a risk factor for the more prevalent small fibre neuropathy.19 A number of these SCN9A variants that were driving the association with painful diabetic neuropathy have previously had functional analysis supporting gain of function.