Does type 2 diabetes mellitus promote intervertebral disc degeneration?

PURPOSE: LDD is an important cause of low back pain. Many people believe there is an adverse influence of type 2 diabetes (T2D) on lumbar intervertebral disc degeneration (LDD). We examined a population sample for epidemiological evidence of association. METHODS: Twin volunteers from the TwinsUK cohort having spine magnetic resonance (MR) scans coded for LDD and information about T2D were investigated in two ways. First, as a population sample and second as a cotwin case control study in twin pairs discordant for T2D. Other risk factors for LDD considered were age, body-mass index (BMI), smoking, and alcohol. RESULTS: In 956 twin volunteers T2D had a prevalence of 6.6 %. LDD score was higher in T2D twins (14.9 vs 13.1 p = 0.04) but was not an independent risk factor if the influence of age and BMI were included in the model. Discordant twin analysis (n = 33 pairs) showed no significant difference in LDD between twins having T2D and their unaffected cotwins. CONCLUSIONS: Twins having T2D did manifest higher LDD scores but the effect was abrogated once BMI was included in multivariable analysis, showing it is not an independent risk factor for LDD. The population study had 80 % power at 0.1 significance level to detect a difference of 1.8 in LDD score (range of 0-60), so if there is an effect of T2D on LDD, it is likely to be small.

Neuropathic pain as part of chronic widespread pain: environmental and genetic influences.

Chronic widespread pain (CWP) has complex aetiology and forms part of the fibromyalgia syndrome. Recent evidence suggests a higher frequency of neuropathic pain features in those with CWP than previously thought. The aim of this study was to determine the prevalence of neuropathic pain features in individuals with CWP and to estimate the influence of genetic and environmental factors on neuropathic pain in CWP. Validated questionnaires (the London Fibromyalgia Screening Study questionnaire and PainDETECT questionnaire) were used to classify twins as having CWP and neuropathic pain, respectively. The prevalence of CWP was 14.7% (n = 4324), and of the 1357 twins invited to complete neuropathic pain screening, 15.9% of those having CWP demonstrated features of neuropathic pain. Neuropathic pain was found to be heritable (A = 37%; 95% confidence interval [CI]: 23%-50%) with unique environmental factors accounting for 63% (95% CI: 49%-79%) of the variance. Heritability of neuropathic pain and CWP were found to be correlated, 0.54 (95% CI: 0.42-0.65). Increasing age, raised body mass index, female gender, and smoking were all risk factors for neuropathic pain (P < 0.05), and CWP (P < 0.05). High socioeconomic status showed negative correlation with neuropathic pain (P = 0.003) and CWP (P = 0.001). Bivariate analysis of the 2 pain traits revealed that genetic predisposition to neuropathic pain is shared with that for CWP. This is the first study to provide formal heritability estimates for neuropathic pain in CWP. The findings suggest that at least some of the genetic factors underlying the development of neuropathic pain and CWP are the same.

Genetic and Environmental Factors in Age-Related Hearing Impairment.

Age-related hearing impairment (ARHI) is a common condition with complex etiology but a recognized genetic component. Heritability estimates for pure tone audiogram-determined hearing ability lie in the range 26-75%. The speech-in-noise (SIN) auditory test, however, may be better at encapsulating ARHI symptoms, particularly the diminished ability to segregate environmental sounds into comprehendible auditory streams. As heritability of SIN has not previously been reported, we explored the genetic and environmental contributions to ARHI determined by SIN in 2,076 twins (87.8% female) aged 18-87 (mean age 54.4). SIN was found to be significantly heritable (A, unadjusted for age=40%; 95% confidence intervals, CI=32%-47%). With age adjustment, heritability fell (A=25%; 95% CI=16-33%), and a relatively strong influence of environmental exposure unshared within twin siblings was identified (E=75%). To explore the environmental aspects further, we assessed the influence of diet (through the Food Frequency Questionnaire, FFQ), smoking (through self-report and cotinine metabolite levels) and alcohol intake (through the FFQ). A negative influence of high cholesterol diet was observed after adjustment (p=.037). A protective effect of raised serum high-density lipoprotein (HDL) cholesterol levels was observed after adjustment (p=.004). This study is the first assessment of the genetic and environmental influence on SIN perception. The findings suggest SIN is less heritable than pure tone audiogram (PTA) ability and highly influenced by the environment unique to each twin. Furthermore, a possible role of dietary fat in the etiology of ARHI is highlighted.