Objective: To examine the prevalence of widespread musculoskeletal pain (WSP) symptoms in 11-year-old Finnish twins and to determine the relative role of genetic and environmental factors in the etiology of WSP.
Methods: Data on current pain items were collected from 1995 to 1998 from a national sample of Finnish families with 11-year-old twins born between 1984 and 1987. The presence of WSP was determined using a validated questionnaire method. Pairwise similarity was computed for 583 monozygotic (MZ) pairs, 588 same-sex dizygotic (DZ) pairs, and 618 opposite-sex DZ twin pairs. Variance components for genetic and environmental factors were estimated using biometric structural equation modeling techniques.
Results: The prevalence of WSP was 9.9%, with no sex difference. The majority of twin pairs with WSP were discordant. The tetrachoric correlations for male MZ (r = 0.38), male DZ (r = 0.37), female MZ (r = 0.59), female DZ (r = 0.54), and opposite-sex pairs (r = 0.43) showed little difference by zygosity. Female pairs were more concordant than male pairs among both MZ and DZ twins. Biometric model-fitting indicated that genetic factors did not account for the pattern of twin similarity. Among boys 35%, and among girls 56%, of the variation in liability to WSP could be attributed to shared familial environmental effects. The remainder was attributed to unshared environmental effects.
Conclusion: Genetic factors seem to play at most a minor role in WSP in 11-year-old twins, and environmental factors shared by family members account for a substantial proportion of the variability in WSP.