Self-Reported Scoliosis is Not a Valid Method for Estimating Concordance Rates of Adolescent Idiopathic Scoliosis in a Danish Twin Population

Abstract

Introduction The etiology of adolescent idiopathic scoliosis is still unclear and the true mode of inheritance has yet to be established. From the Danish twin cohort concordance rates in monozygotic twins have previously been reported to be 0.13 and in dizygotic twins 0. Studies on concordance in twin pairs provide a basis for analyzing the influence of genetic versus environmental factors. In this study, we wanted to validate if self-reported scoliosis is a valid method to establish incidence and concordance rates in a twin population. Patients and 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. The questionnaire was returned by 34,944 (75.3%) representing 23,204 pairs. A total of 548 individuals representing 274 complete twin pairs, where at least 1 has self-reported scoliosis were invited to a clinical and a radiologic examination. Zygosity was established by genetic testing. Results A total of 182 individuals (33.2% of the cohort) participated. Overall, 128 of these individuals had self-reported scoliosis. The total number of participants consisted of 91 twin pairs, where one or both twins had scoliosis and 36 individuals whose twin did not want to participate. Overall, 35 individuals (27.3%) of the 128 participants with self-reported scoliosis presented a clinical and radiological confirmed curve. Of these were 5 twin pairs (four monozygotic pairs and one dizygotic pair) with scoliosis in both twins and 16 twin pairs with scoliosis in only 1 twin and 9 individuals where only one twin participated. Calculating concordance in twins with curves greater than 10 degrees, we found that the pairwise concordance rate was 0.4 (range, 0.12–0.74) for monozygotic and 0.05 (range, 0.01–0.25) for dizygotic twin pairs, probandwise concordance was 0.45 for monozygotic and 0.1 for dizygotic pairs. Conclusion Self-reported scoliosis in a Danish twin population is not a valid method to establish the true concordance rates. Although it is not statistically significant the differences in monozygotic and dizygotic pairs indicate that hereditary parameters have an impact.