Univariate analyses of AP, AGG, and A/D in consecutive cohorts of 7,10, and 12 year-old twin pairs: Gender and developmental findings

Twin, family, and molecular genetic studies have investigated the genetic contribution to common child syndromes such as attention problems (AP), aggressive behavior (AGG) and Anxious/Depressed behavior (A/D). Twin studies of DSM-IV related disorders such as ADHD indicate that as much as 94% of the influence on this common condition is due to genetic factors. Prior research on the AP scale of the CBCL indicate approximately 64% of the variance is due to genetic factors. Few studies have had the power to assess for informant (mother repon versus father report), gender and developmental (effects at age 7, 10, and 12) contributions to these syndromes. The purpose of this study was to assess for the genetic, environmental, informant, developmental, gender, and rater contrast contributions to AP, AGG, and A/D in 7, 10 and 12 year old twin pairs. Methods: CBCL data from mothers on 3548 7-year-old, 2591 10-year-old, and 1085 12-year old twin pairs and CBCL data from fathers on 2807 7 year-old, 1987 10-year-old, and 885 12 year-old twin pairs from the Netherlands Twin registry were analyzed. Contributions from additive (a), dominant (d), shared environmental (c), unique environmental (e) and rater-contrast effects were computed using gender-genetic models on mother and father reports of the same twins when they were 7, 10, and 12 years old. Results: Evidence for moderate genetic influences were found for all three syndromes at each age. Best fitting models for AGG and A/D were Aei models, which include moderate genetic affects, unique environmental and very small interaction effects. There was not evidence of genetic dominance. Sex differences are reported. Differences in genetic influ-ence by age are also found, with percent of genetic variance decreasing by age. Fathers generally reported data that yielded lower genetic influence than mothers. Analysis of the ATT data however yielded two competing models. The Aei model, which fit best for AGG and A/D also fit well for ATT, demonstrating that > 70% of the variance on ATT was due to additive genetic factors. However, for each of our analyses on ATT, the best fitting model was one that included genetic dominance, this ADE model, yielded evidence that the influence on ATT was equal parts additive genetic, unique environmental, and dominant genetic. These results were consistent for our analyses across age, gender, and informant. Discussion: We have demonstrated gender, informant and developmental effects on the genetic and environmental influences on ATT, AGG, and A/D. We have demonstrated that genetic dominance may play a role in attention problems, a finding that competes with the typical results of additive and unique environmental factors as influencing ATT. We demonstrate Aei models for AGG and A/D across development and gender. Informant, gender, and developmental affects are many and will be presented. The competing Aei and ADE models for ATT will be discussed in the context of genetic dominance.