Two of those mutations (I381T and L1158P) led to a reduction in the current threshold and increased firing frequency in response to suprathreshold stimuli, resulting in increased excitability of DRG neurons.[68] Zhang et al. (2013) also described two mutations in the SCN11A gene (R225C and A808G) in patients experiencing episodic chronic pain.[69] Another Nav1.9 mutation, G699R, which is located in the DII/S4-5 linker, has been identified in a patient with symptoms of painful small fiber neuropathy. This evidence concerns the gene SCN11A and neuropathy, small fiber.