Table 3

Intraclass correlations, modelling and heritability estimates for the MRI traits by age category

Age, years∆Trait/time (per year)N pairs (monozygotic)N pairs (dizygotic)R-monozygotic (95% CI)R-dizygotic (95% CI)A (95% CI)C (95% CI)
<50Disc height18530.51 (0.16 to 0.87)0.53 (0.33 to 0.72)0.51 (0.30 to 0.71)
50–60Disc height50630.33 (0.076 to 0.57)0.40 (0.19 to 0.62)0.37 (0.19 to 0.54)
>60Disc height22280.18 (0.00 to 0.63)0.47 (0.17 to 0.77)0.38 (0.10 to 0.65)
<50Disc signal18530.71 (0.48 to 0.95)0.41 (0.18 to 0.63)0.76 (0.44 to 1.0)
50–60Disc signal50630.37 (0.13 to 0.61)0.34 (0.11 to 0.57)0.36 (0.18 to 0.54)
>60Disc signal22280.45 (0.08 to 0.81)0.48 (0.18 to 0.78)0.41 (0.14 to 0.68)
<50Disc bulge18530.39 (0.0 to 0.80)0.10 (0.00 to 0.37)0.28 (0 to 0.65)
50–60Disc bulge50630.56 (0.38 to 0.75)0.16 (0.00 to 0.41)0.51 (0.28 to 0.74)
>60Disc bulge22280.55 (0.24 to 0.86)0.34 (0.00 to 0.68)0.53 (0.13 to 0.94)
<50Anterior osteophytes18530.71 (0.49 to 0.94)0.40 (0.18 to 0.63)0.74 (0.42 to 1.0)
50–60Anterior osteophytes50630.58 (0.40 to 0.77)0.58 (0.42 to 0.75)0.58 (0.43 to 0.74)
>60Anterior osteophytes22280.60 (0.31 to 0.89)0.56 (0.29 to 0.82)0.57 (0.32 to 0.81)
<50Summary score18530.57 (0.24 to 0.89)0.12 (0.00 to 0.39)0.40 (0.06 to 0.73)
50–60Summary score50630.42 (0.19 to 0.65)0.31 (0.08 to 0.55)0.48 (0.24 to 0.72)
>60Summary score22280.39 (0.00 to 0.77)0.48 (0.18 to 0.78)0.40 (0.13 to 0.67)
  • Heritability was calculated using 90 monozygotic and 144 dizygotic same-sex twin pairs (omitted when dizygotic intraclass correlation greater than monozygotic intraclass correlation clearly suggests no heritable component) when N is the sample size in twin pairs by age subgroup. Age category 0=age <50 years, category 1=age. ∆Trait/time per year represents change in trait per year. A represents additive genetic, C common environment and E unique environmental factors.