Shared and unique genetic vulnerability of mood and substance use disorders to address the dual diagnosis versus co-occurrence hypotheses.
Mental illness accounts for large proportions of the global burden of disease, worldwide. Among those disorders, the co-occurrence of mood and substance use disorders is the rule rather than the exception. Individuals with such "dual" disorders suffer from complicated course of illness and poor functioning, as compared to those with single disorders. To date, the biological underpinnings of developing dual vs. single mental disorders remain unknown. Polygenic factors are very likely to be involved in this biological liability. The identification of profiles associated with more complicated mental disorders is a key issue in order to develop personalized psychiatry. This can be achieved by modelling the combined genetic, cognitive and clinical markers of single vs. comorbid psychiatric disorders at various stages of illness. Such modelisation requires large, well-characterized human samples.