Lens fluorescence and skin fluorescence in the Copenhagen Twin Cohort Eye Study: Covariates and heritability

Lens and skin fluorescence are related to the systemic accumulation of
advanced glycation end products, which is accelerated in diabetes. We have
examined lens fluorescence and skin fluorescence in healthy adult twins.
The study enrolled twins aged median 59 years from a national
population-based registry. Diabetic individuals were excluded from
analysis. The interrelatedness between fluorescence parameters and
relations between fluorescence and age, current HbA1c and smoking pack
years were examined using correlation tests and mixed model linear
regression analyses. Broad-sense heritability was analyzed and compared
for lens fluorescence, skin fluorescence and HbA1c. Lens fluorescence and
skin fluorescence were crudely interrelated (R = 0.38). In linear
regression analyses, age explained a larger fraction of the variance in
lens fluorescence (R2 = 32 %) than in skin fluorescence (R2 = 20 %),
whereas HbA1c explained smaller variance fractions (R2 = 3 % and 8 %,
respectively) followed by smoking pack years (4 % and 3 %, respectively).
In multivariate analyses, age, HbA1c and smoking pack years combined
explained more of the variance in lens fluorescence (R2 = 35 %) than in
skin fluorescence (R2 = 21 %), but the influence of HbA1c on lens
fluorescence was not statistically significant (p = .2). Age-adjusted
broad-sense heritability was 85 % for lens fluorescence, 53 % for skin
fluorescence and 71 % for HbA1c in best fitting heritability models. Both
fluorescence parameters increased with age, current glycemia and
cumulative smoking. Lens fluorescence was found to be a predominantly
heritable trait, whereas skin fluorescence was more influenced by
environmental factors and closer related to current glycemia. The results
suggest that skin fluorophores have a faster turn-over than lens
fluorophores.