Comorbidities and psychotic illness. Part 1: Philosophy and clinical consequences.

This article aims at addressing the implications of defining 'comorbidity' within the field of psychiatry. We have looked at the standard definition of comorbidity and then discussed whether this definition can be applied to comorbidities in psychiatry. While comorbidities in physical illness are clearly the coexistence of two independent illnesses, Comorbidities in Mental illness are the result of the polygenic nature of mental illnesses, especially in psychotic illness whether schizophrenia or bipolar disorder. As a consequence, often the comorbidities of psychiatric illness are caused by two conditions which have in common the presence of particular single nucleotide polymorphisms (snps), which regulate the metabolism of neurotransmitters or the presence of neurotrophic factors . Thus inevitably, many such comorbidities are inextricably linked. We discuss the consequences of this form of comorbidity for the description, classification, and risk profile of mental illness.