Pain
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Neuropathic pain conditions are common after nerve injuries and are suggested to be regulated in part by genetic factors. We have previously demonstrated a strong genetic influence of the rat major histocompatibility complex on development of neuropathic pain behavior after peripheral nerve injury. In order to study if the corresponding human leukocyte antigen complex (HLA) also influences susceptibility to pain, we performed an association study in patients that had undergone surgery for inguinal hernia (n=189). ⋯ This finding was subsequently replicated in the clinical material of patients with lumbar disc herniation (n=258), where carriers of the DQB1*03:02 allele displayed a slower recovery and increased pain. In conclusion, we here for the first time demonstrate that there is an HLA-dependent risk of developing pain after surgery or lumbar disc herniation; mediated by the DRB1*04 - DQB1*03:02 haplotype. Further experimental and clinical studies are needed to fine-map the HLA effect and to address underlying mechanisms.
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Single nucleotide polymorphisms (SNPs) in the serotonergic (5HT) system seem to have modulatory effects on depression and physical function. Preliminary evidence suggests that gene×environment interactions play a role in the development of depression, with somatic complaints serving as environmental stressors. We hypothesized that pain intensity may serve as a stress factor that modulates the association between SNPs in the 5HT system and depression. ⋯ Furthermore, women homozygous for either the 5HTR1A G allele or the 5HTR2A A allele had lower levels of physical functioning than patients with the other genotypes. These results suggest that 5HTR1A and 5HTR2A promoter variations have gender-dependent modulatory effects on depression and physical function in patients with pain. Furthermore, this study demonstrates that pain after lumbar surgery modulates the association between 5HT gene polymorphisms and depression.
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Theoretical accounts of chronic pain hypothesize that attentional bias towards pain-related information is a maintaining or exacerbating factor, fuelling further pain, disability, and distress. However, empirical research testing this idea is currently lacking. In the present study, we investigated whether attentional bias towards pain-related information predicts daily pain-related outcomes in a sample of chronic pain patients (n=69; M(age)=49.64 years; 46 females). ⋯ Results indicated that, although an attentional bias towards pain-related information was associated with the current level of disability and pain severity, it had no additional value above control variables in predicting daily pain severity, avoidance, distractibility, and disability. Attentional bias towards pain-related information did, however, moderate the relationship between daily pain severity and both daily disability and distractibility, indicating that, particularly in those patients with a strong attentional bias, increases in pain were associated with increased disability and distractibility. The use of interventions that diminish attentional bias may therefore be helpful to reduce daily disability and the level of distraction from current tasks despite the presence of pain in chronic pain patients.