The use of genetic epidemiology to guide classification in child and adult psychopathology.

The goal of this paper is to illustrate the application of the tools of genetic epidemiology, particularly the family study method, to inform the classification of psychiatric disorders in adults and children. The first section describes family studies of adults designed to investigate the causes of comorbidity of anxiety and depression. The analysis of familial traits provides stronger evidence for the validity of certain sub-types of anxiety and mood disorders that co-occur within the same individual and within families. The second section presents an example of the use of the family study method to examine the validity of the autism spectrum disorders (ASD). A review of these studies suggests that the most consistently familial traits in ASD are language and communication skills, insistence on sameness and non-verbal IQ. These are also the traits most commonly associated with the differentiation of autism from Asperger disorder and PDDNOS using both cross-sectional and longitudinal studies. From these data, a new classification system of the ASDs is proposed based on these familial traits.