None of the above studies were conducted on genetically informative samples, leaving unanswered the question of differences in genetic influences across diagnostic criteria. Familial aggregation is considered one key validator for psychiatric illness (Kendler, 1990; Robins and Guze, 1970): therefore, it is of interest whether the DSM-IV and DSM-5 diagnoses are similarly genetically influenced, both in terms of total heritability and potential qualitative differences in the underlying genetic factors. In other words, is a DSM-5 diagnosis informative of familial risk to the same extent that a DSM-IV diagnosis does? Do the two diagnoses reflect the same underlying genetic liability or is the new diagnosis influenced by novel genetic factors? To our knowledge, this question has not yet been addressed by studies exploring the ramifications of changes in diagnostic criteria.
