Biomarkers in Schizophrenia: Current Approaches and New Developments-A Literature Review

Schizophrenia (SZ) is categorized as a chronic severe highly heritable brain disease. Symptoms include positive, negative, and cognitive symptoms. Despite numerous theories concerning the etiopathogenesis of SZ, the symptoms, although characteristic in their phenomenology, manifest themselves in a rather heterogeneous manner, which makes them subject to clinical assessment and, at the same time, prone to errors resulting from diverse interpretations of the context of the patient's statements. Therefore, current research is focusing on identifying more subtle and stable features of SZ, such as the phenotype, endophenotype, and assessable abnormalities devoid of human clinical observation. The various biomarker developments focus on the role of transmitters and their corresponding receptors, in particular: glutamate, acetylcholine, dopamine, or serotonin. Also important in terms of etiopathogenesis remain growth factors such as brain-derived neurotrophic factor (BDNF), nerve growth factor receptor (NGFR), or vascular endothelial growth factor (VEGF). More recently, research has emphasized the role of inflammatory processes and secreted pro- as well as anti-inflammatory cytokines, included in the class of interleukins, chemokines, and tumor necrosis factors, as well as on inflammatory markers-C-reactive protein (CRP) or glutathione (GSH). Increasingly, changes at the genetic level have been implicated as the cause of diseases, and it is now believed that noncoding RNAs (micro-RNA [miRNA], long noncoding RNA [lnc-RNA], and circular RNA [circRNA]) are involved in the development of SZ. Among the genes that may prove to be potential biomarkers in SZ belong SEDT1A, FOXP2, GRIN2A, GRIA3, NRN1, BDNF, CACNA1C, and ZNF8A4. The peptide group molecules, Phospholipase A2, Klotho protein, and soluble urokinase plasminogen activator receptor (suPAR), also remain consistently important. From the perspective of SZ as a disease associated with neuronal damage, biomarkers correlating with brain injury, neuron-specific enolase (NSE), and S100B protein should be considered.