Adolescent idiopathic scoliosis in twins - A population-based survey

Study Design. A questionnaire-based identification of adolescent idiopathic scoliosis (AIS) patients in a twin cohort. Objective. The purpose of this study was to establish a scoliosis twin cohort to provide data on the heritability of AIS. Summary of Background Data. The etiology of AIS is still unclear, and the true mode of inheritance has yet to be established. Concordance rates in monozygotic twins have been reported to be between 0.73 and 0.92, and in dizygotic twins between 0.36 and 0.63. Studies on concordance in twin pairs provide a basis for analyzing the influence of genetic versus environmental factors. Methods. All 46,418 twins registered in the Danish Twin Registry born from 1931 to 1982 were sent a questionnaire, which included questions about scoliosis. A total of 34,944 (75.3%) representing 23,204 pairs returned the questionnaire. Results. A subgroup of 220 subjects considered to have AIS was identified, thus giving a prevalence of 1.05%. The concordant twin pairs were all monozygotic. Pairwise, the concordance rate was 0.13 for monozygotic and zero for dizygotic twin pairs; proband-wise concordance was 0.25 for monozygotic and zero for dizygotic pairs. The concordance of monozygotic and dizygotic pairs was significantly different (P < 0.05). Conclusion. We have found evidence for a genetic etiology in AIS, but the risk of developing scoliosis in 1 twin whose other twin has scoliosis is smaller than believed up until now.