OPRM1 and diabetic neuropathy: OPRM1 encodes the MOR, which has a key role in endogenous pain modulation.56 A recent meta-analysis examining the common variant in OPRM1 (c.A118G; p.Asn40Asp) did not find significant association with neuropathic pain.64 However, we found 4 rare OPRM1 variants overrepresented in the painful diabetic neuropathy group; these have previously undergone investigation for their impact on MOR signaling.