Heritability of scoliosis.

PURPOSE: To estimate the heritability of scoliosis in the Swedish Twin Registry.

METHODS: Self-reported data on scoliosis from 64,578 twins in the Swedish Twin Registry were analysed. Prevalence, pair- and probandwise concordances and tetrachoric correlations in mono- and dizygotic same-sex twins were calculated. The relative importance of genetic variance, i.e. the heritability, and unique and shared environmental variance was estimated using structural equation modelling in Mx software. In addition, all twins in the twin registry were matched against the Swedish Inpatient Register on the primary diagnosis idiopathic scoliosis.

RESULTS: The prevalence of scoliosis was 4%. Pair- and probandwise concordance was 0.11/0.17 for mono- and 0.04/0.08 for same-sex dizygotic twins. The tetrachoric correlation (95% CI) was 0.41 (0.33-0.49) in mono- and 0.18 (0.09-0.29) in dizygotic twins. The most favourable model in the Mx analyses estimated the additive genetic effects (95% CI) to 0.38 (0.18-0.46) and the unique environmental effects to 0.62 (0.54-0.70). Shared environmental effects were not significant. The pairwise/probandwise concordance for idiopathic scoliosis in the Swedish Inpatient Register was 0.08/0.15 for monozygotic and zero/zero for same-sex dizygotic twins.

CONCLUSION: Using self-reported data on scoliosis from the Swedish Twin Registry, we estimate that 38% of the variance in the liability to develop scoliosis is due to additive genetic effects and 62% to unique environmental effects. This is the first study of sufficient size to make heritability estimates of scoliosis.