Association of the functional A118G polymorphism of OPRM1 in diabetic patients with foot ulcer pain

Background: Diabetic foot ulcer (DFU) patients may experience moderate or severe pain. A single-nucleotide polymorphism, at nucleotide 118 for opioid receptor mu 1 (OPRM1), has been reported to alter the opioid effects to relieve acute or chronic pain. The purpose of this study was to elucidate the correlation between nucleotide 118 variants and foot ulcer pain in DFU patients. Methods: Sixty-five DFU patients with Grade 2-5 Wagner-Meggitt classification were enrolled. The occurrence of pain in activities was categorized into five grades. Patients were allocated either into the painless DFU group, with a visual analog scale (VAS) pain score <= 3, or into the painful DFU group, with a VAS pain score >= 4 and Grades 3-5 of occurrence of pain in daily activities. DNA was extracted from blood samples of analyzed patients. Using the polymerase chain reaction-single-strand conformation polymorphism analysis and DNA sequencing of nucleotide 118, we identified the genotype distribution and allelic frequencies in DFU patients. The sequences of the forward and the reverse primer are designed as follows: 5'-TAATACGACTCACTATAGGG-3' and 5'-ACGCACACGATGGAGTAGAG-3', respectively. Results: Fifteen patients were classified into the painful DFU group and 50 patients were classified into the painless DFU group. The amplified DNA fragments showed 26 homozygous (AA), 34 heterozygous (AG), and 5 mutant homozygous (GG) genotypes, with overall A and G allelic frequencies of 66.2% and 33.8%, respectively. The painful DFU group included 10 AA subjects, 4 AG subjects, and 1 GG subject, while the painless DFU group had 16 AA, 30 AG, and 4 GG subjects (P=.038). Conclusion: The A118G polymorphism of mu-opioid receptor may be closely associated with DFU pain in 34 out of 50 patients in the painless group and in 5 out of 15 patients in the painful group. This indicates that the nucleotide 118 variant patients may suffer less DFU pain. (C) 2010 Elsevier Inc. All rights reserved.