Interpreting Genetic Studies of Childhood Psychiatric Disorders

Interpreting Results of Genetic Studies

• Diagnostic categories do not closely map genetic factors in aetiology, making it challenging to identify specific genetic causes for childhood psychiatric disorders.
• Phenotypes, such as autism spectrum disorders, can include multiple symptoms, including developmental language disorders, while Gilles de la Tourette syndrome's phenotype extends to obsessional thinking and behavior.

Comorbidity

• Many children exhibit symptoms that qualify for multiple psychiatric diagnoses, such as depressive disorder and conduct disorder, or depressive disorder and eating disorder.
• It is unclear whether one disorder predisposes to another or if they are two manifestations of the same genetic predisposition.

Polygenic Effects and Environmental Influences

• Hereditary factors in child psychiatry are largely polygenic, meaning they involve multiple genes interacting with psychosocial factors.
• Genetic investigations may include estimates of environmental factors that influence gene expression.

Indirect Effects of Genes

• Genes can exert their effects through factors such as intelligence and temperament, which in part determine whether certain situations are experienced as stressful.

Shared and Non-Shared Environment

• Analyses of population genetic data divide variance into genetic, shared environmental, and non-shared environmental factors.
• Twins, full siblings, and half-siblings are used as comparison groups in studies to distinguish between shared and non-shared environmental factors.
• The assumption that sibling comparison groups share similar environments has limitations, as a shared environment can affect different children differently, appearing as 'non-shared environment' in analyses.