Objective: A classical twin study was performed to assess the relative contribution of genetic and environmental factors to cartilage volume.
Methods: The subjects were 136 adult female twins: 31 monozygotic and 37 dizygotic twin pairs. The subjects had a T2-weighted fat-saturated sagittal gradient echo MRI performed of their right knee. Femoral, tibial and patella cartilage volumes were measured using 3D Slicer, a piece of software that facilitates semi-automatic segmentation, generation of three-dimensional surface models and quantitative analysis. The intraclass correlations were calculated, and maximum-likelihood model fitting was used to estimate genetic and environmental variance components. All variables were adjusted for age, BMI and femoral condyle size.
Results: The intraclass correlations for all of the cartilage volumes assessed were higher in monozygotic than dizygotic twin pairs. The heritabilities (95% confidence intervals) obtained from model fitting were: femoral, 61% (36-77%); tibial, 76% (56-87%); patella, 66% (47-79%); and total cartilage volume, 73% (51-85%).
Conclusion: This study provides evidence for the importance of genetic factors in determining cartilage volume. Identifying heritability is the first step on the way to finding specific genes, which may improve our insight in the pathophysiology of cartilage disorders including the etiology of complex diseases such as osteoarthritis.