Genetic influence on parent-reported attention-related problems in a Norwegian general population twin sample.

To assess the genetic and environmental influences on attention problems in a general population twin sample and to investigate whether there are changes in the relative genetic influence on attention problems with increasing severity. Parental ratings of the Child Behavior Checklist were collected from five Norwegian national cohorts of same-sex twins. The sample comprises 526 identical and 389 fraternal pairs. Considerable genetic influence on attention problems was found for both sexes and across age groups (aged 5 to 9 years and 12 to 15 years). A two-parameter model with additive genetic influence and nonshared environment showed a good fit, with heritability ranging from .73 in boys aged 5 to 9 years, to .76 in girls aged 5 to 9 years. There was no change in the relative genetic influence across severity after accounting for the influence of cerebral palsy, epilepsy, and low birth weight. The results indicate a substantial genetic influence on attention problems across sex, age, and severity.