Observer effects and heritability of childhood attention-deficit hyperactivity disorder symptoms

Twin studies have found that childhood attention-deficit hyperactivity disorder (ADHD) has a strong genetic component. Estimates of heritability, the extent of non-additive genetic effects and of 'sibling contrast' effects vary between different studies.

To use multiple informants to assess the extent to which observer effects influence such estimates in an epidemiological sample of twins.

Questionnaire packs were sent to the families and teachers of twins aged 5-16 years in the Bro Taf region of South Wales. The twins were ascertained from community paediatric registers.

Both parent- and teacher- rated data showed a high degree of heritability for ADHD measured as a symptom dimension, but the correlation between the two types of rater was modest. Bivariate analyses suggested that parent and teacher ratings reflect the effects of different genes. Self-report data from twins aged 11-16 years showed no evidence of genetic effects.

Although ADHD is shown to be highly heritable by both parent- and teacher-rated data, the underlying genotypes may be substantially different. This has implications for study designs aiming to find genes that contribute to the disorder.