Determinants of pressure pain threshold in adult twins: evidence that shared environmental influences predominate.

The objective of this study was to examine the relative contribution of genetic and environmental factors in determining pain perception in a classical twin study. Dolorimeter measurements of pressure pain threshold (PPT) were recorded in 609 healthy female-female twin pairs of whom 269 pairs were monozygotic (MZ) and 340 were dizygotic (DZ). There was a strong correlation (R) in PPT in both MZ and DZ pairs (R(MZ) = 0.57, 95% confidence interval (CI): [0.49, 0.65]; R(DZ) = 0.51, 95% CI: [0.42, 0.59]). The slight excess in intraclass correlation observed in MZ when compared with DZ twins corresponds to a heritability for PPT of only 10% and is not statistically significant. Neither estimate of intraclass correlation was substantially altered after adjusting for a range of potential confounding variables including age, current tobacco and alcohol use, current analgesic use, psychological status assessed by the general health questionnaire, and social class. The dolorimeter measurements were shown to be reliable (between observer agreement R = 0.66; within observer agreement R = 0.70-0.76) and stable over time. In conclusion, these data suggest that there is no significant genetic contribution to the strong correlation in PPT that is observed in twin pairs. These findings reinforce the view that learned patterns of behaviour within families are an important determinant of perceived sensitivity to pain.