Similarly, we found age differences in variance components for 62 traits. In some cases, these differences affected the genetic variance; in other cases, they affected environmental variances; and in still other cases, they affected the total variance. In the majority of cases in which we saw a difference in heritabilities between the young and old, we observed higher heritabilities among younger individuals. The trend likely reflects an expected increase of environmental insults with age [47]. Nevertheless, important exceptions were present, including traits such as SBP, DBP, mean blood pressure, and pulse pressure, whose heritability increased an average of 18% among older individuals. Interestingly, some measures of vascular structure and function (such as PWV, which reflects autonomous stiffening of the arterial substrate) that change markedly with age, showed no significant differences in variance components between young and old individuals. Taken together, these results suggest that it will often be fruitful to examine genetic effects separately by sex and age groups. In some instances, our results may allow investigators to focus molecular studies on groups that show higher heritability.
