Approaches to gene mapping in complex disorders and their application in child psychiatry and psychology

Background: Twin studies demonstrate the importance of genes and environment in the aetiology of childhood psychiatric and neurodevelopmental disorders. Advances in molecular genetics enable the identification of genes involved in complex disorders and enable the study of molecular mechanisms and gene-environment interactions. Aims: To review the role of molecular genetics studies in childhood behavioural and developmental traits. Method: Molecular approaches to complex disorders are reviewed, with examples from autism, reading disability and attention-deficit hyperactivity disorder (ADHD). Results: The most robust finding in ADHD is the association of a variable number tandem repeat polymorphism in exon 3 of the DRD4 gene. Other replicated associations with ADHD are outlined in the text. In autism, there is a replicated linkage finding on chromosome 7. Linkage studies in reading disability have confirmed a locus on chromosome 6 and strongly suggest one on chromosome 15. Conclusions: In the next 5-10 years susceptibility genes for these disorders will be established. Describing their relationship to biological and behavioural function will be a far greater challenge.