LENS THICKNESS AND INSULIN-DEPENDENT DIABETES-MELLITUS - A POPULATION-BASED TWIN STUDY

Aim - To investigate the relation between lens thickness and duration of insulin dependent diabetes mellitus (IDDM). Methods - From the new population based Danish twin register, containing 20 888 twin pairs bo rn between 1953 and 1982 (inclusive), all twin pairs having one or bot h partners affected with IDDM were searched. Among the 45 twin pairs a vailable for clinical eye examination there were 15 monozygotic pairs, 14 dizygotic pairs of same sex, and 16 dizygotic pairs of opposite se x. Lens thickness was measured by ultrasonography. Using a twin contro l design, the relation between lens thickness and duration of IDDM was assessed by estimating the correlation between the intrapair differen ce in lens thickness and the intrapair difference in diabetes duration . Results - In monozygotic twin pairs a statistically highly significa nt correlation between duration of diabetes and lens thickness was fou nd (right eye: r=0.88, p<0.0001; left eye: r=0.90, p<0.0001). In dizyg otic twin pairs of the same sex the correlations were r=0.58 (p=0.029) and r=0.53 (p=0.053) for right eye and left eye, respectively. For di zygotic twin pairs of opposite sex the correlations were r=0.58 (p=0.0 18) and r=0.69 (p=0.005) for right eye and left eye, respectively. The slope in regression analysis were similar for monozygotic twin pairs (0.025, common for both eyes) and dizygotic twin pairs grouped (0.024, common for both eyes). Conclusions - There is a statistically signifi cant positive correlation between duration of IDDM and lens thickness, as assessed by the twin control method. The higher correlation in mon ozygotic twins compared with dizygotic twins suggests that genetic fac tors play an additional role in the determination of lens thickness. T he similar slopes in regression analysis indicate that the effect of d iabetes duration on lens thickness is independent of zygosity.