Blood ATX(N) Biomarkers and Cognitive Dysfunction in Severe Mental Illnesses.

Psychiatric disorders, such as major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SZ), comprise a heterogenous group of severe mental illnesses (SMIs) characterized by disturbances in cognition, emotional regulation, or behavior. Cognitive impairment represents an accompanying feature of many SMIs, often interfering with or limiting essential daily life activities. SMIs arise from a complex interplay of genetic, epigenetic, developmental, and environmental factors that disrupt neural and cellular processes. SMIs often present with overlapping symptoms and sometimes co-occur, making misdiagnosis a common clinical challenge. To date, there is a lack of reliable and specific biological markers to aid in the differential diagnosis of cognitive impairment in SMIs and for distinguishing neurodegenerative dementias from SMIs with overlapping symptoms. In this context, blood-based biomarkers of the ATX(N) system associated with cognitive deficits in neurodegenerative diseases, such as neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), amyloid beta (Aβ), and tau proteins, may help to understand the biological basis of cognitive dysfunction in SMIs and support differential diagnosis. This narrative review summarizes the current evidence on the application of blood-based biomarkers of neurodegenerative dementias in SMIs and their association with the cognitive deficits observed in these conditions, as well as their relevance for differential diagnosis, disease monitoring, and the evaluation of treatment efficacy in psychiatric disorders.