Widespread pain among 11-year-old Finnish twin pairs

Objective. To examine the prevalence of widespread musculoskeletal pain (WS P) 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 19 84 and 1987. The presence of WSP was determined using a validated questionn aire method. Pairwise similarity was computed for 583 monozygotic (MZ) pair s, 588 same-sex dizygotic (DZ) pairs, and 618 opposite-sex DZ twin pairs. V ariance components for genetic and environmental factors were estimated usi ng biometric structural equation modeling techniques. Results. The prevalence of WSP was 9.9%, with no sex difference. The majori ty 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 zygosit y. Female pairs were more concordant than male pairs among both MZ and DZ t wins. Biometric model-fitting indicated that genetic factors did not accoun t 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 environmen tal 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.