Genetic Components in Scheuermann‘s Disease: A Cohort Study of Twins

Scheuermann‘s disease is the most frequent cause of hyperkyphosis of the thoracic and thoracolumbar spine. Although several theories based on genetic and mechanical factors have been proposed the mode of inheritance and the role of environmental factors are still unknown. The purpose of this study was to examine whether genetic factors contribute to the pathogenesis of Scheuermann‘s disease.

Materials and Methods: The cohort from The Danish Twin Registry used for this study consists of all Danish twin pairs born between 1931 and 1982. Establishment of zygosity has throughout the period been based on four questions of similarity with an accuracy of approximately 95%. All registered twins received a 17-pages “omnibus” questionnaire in the spring of 2002. The total number of twins was 46,418. Of these 34,944 (75%) returned the questionnaire. 34,007 (97.3 %) answered the question “Have you been diagnosed with Scheuermann´s disease?” The overall prevalence of self reported Scheuermann`s disease was calculated using the total number of answers as the general twin population. The pair-wise concordance estimates the probability that both twins are affected in a pair in which one is affected, while the proband-wise estimates the probability that a twin will be affected given that the twin partner is. The pair-wise concordance was compared using the Chi-square test.

All scientific-ethical committees in Denmark have approved the study.

Results: Nine-hundred-and-forty-three of the 34,007 responders reported to have Scheuermann´s disease. 380 females and 563 males. The overall self reported prevalence of Scheuermann‘s disease was 2.8% (95% confidence limits (c.i.l.) 2.6-3.0). Stratified according to gender we found a male and female prevalence of 3.6% (95% c.i.l. 3.2-4.1) and 2.1% (95% c.i.l. 1.9-2.3) respectively, and this difference was statistically significant (Chi-square test 67.8 (P<<0.0001)). The prevalence of Scheuermann‘s disease was not significantly different between the cohorts of monozygotic (MZ) and dizygotic (DZ) twins and the figures were as would be expected from the literature.

Of 11,436 twin pairs in whom both answered the above question 645 indicated that they had been diagnosed with Scheuermann´s disease. The pair-wise concordance was 0.19 (95% c.i.l. 0.13-0.25) for MZ and 0.07 (95% c.i.l. 0.04-0.11) for DZ twin pairs. This difference was statistically significant (Chi-square test 13.3 (P<0 .001)). The proband-wise concordance was 0.31 (95% c.i.l. 0.25-0.37) for MZ and 0.13 0.09-0.17) in DZ twin pairs.

Conclusion: We find an overall prevalence of Scheuermann´s disease as expected from the literature (2.8%), with a strongly significant higher male prevalence of twice the female (3.6 vs. 2.1%).

Both the pair-wise and the proband-wise concordance is between two and three times higher in MZ than in DZ pairs. This higher concordance rate of MZ pairs confirms a contribution of a major genetic component while indicating the need to identify possible environmental triggers.