Genetic epidemiology of Scheuermann's disease Heritability and prevalence over a 50-year period

Background and purpose The genetic/environmental etiology of Scheuermann's disease is unclear. We estimated the heritability of the disease using an etiological model adjusted for sex and time of diagnosis, and examined whether the prevalence of Scheuermann's disease was constant over time. Methods 46,418 twins were sent a questionnaire about health and disease. Of these, 75% returned the questionnaire and 97% answered the question "Have you been diagnosed as having Scheuermann's disease by a doctor?" Results Responders included 11,436 complete pairs of twins. Data were analysed using classical twin modeling methods. Tetrachoric correlations were used to decide which etiological model to fit. The best-fitting model was the AE model. Heritability was 0.74 (95% CI: 0.65-0.81), while variance explained by environmental factors was 0.26 (95% CI: 0.19-0.35). A threshold of 2.1 (95% CI: 1.9-2.2) was calculated, corresponding to a prevalence of 1.9% (95% CI: 1.3-2.8) for women. Regression coefficients for age and sex were 0.000 (95% CI: -0.003 to 0.002) and -0.32 (95% CI: -0.42 to -0.23). Interpretation We found a heritability of 0.74 in Scheuermann's disease. The threshold in men was lower than in women, corresponding to a male prevalence that was almost twice that of females. We found no change in the prevalence of Scheuermann's disease throughout the 50-year age span that we examined.