Schizophrenia

Abstract

Schizophrenia is a severe mental illness with a prevalence of approximately 1%. Its core features are delusions, hallucinations, affective flattening and disorganized behaviors. Although schizophrenia is severe psychiatric disorder, it is classified in the category of common diseases. Many studies have shown a strong genetic component for the development of schizophrenia. Heritability of schizophrenia is estimated to be approximately 80%. The mode of inheritance is multifactorial. Schizophrenia is a common and genetically complex disease. Schizophrenia research has developed rapidly in recent years. This is based on developments in the technology for molecular genetics. The advanced technologies can be used to perform genome-wide association study (GWAS) and copy number variant/variation (CNV) study. GWAS has revealed associations between schizophrenia and ZNF804A, NOTCH4 (major histocompatibility complex region: MHC), NRGN, TCF4, LSM1, BRP44, NFKB, NKAPL and TSPAN18 genes. The CNV study has found associations between schizophrenia and duplications/deletions of 1q21.1, 3q29, 16p11.2, 15q11.2, 15q13.3, 17q12 and 22q11.2 regions. The 22q11.2 deletion is the most interesting region in the genetic etiology of schizophrenia. A patient with 22q11.2 deletion is referred to as having 22q11.2 deletion syndrome (22q11.2DS). This syndrome is also called DiGeorge/Velocardiofacial syndrome. Patients with 22q11.2DS have a high incidence of schizophrenia (~23%). Schizophrenia may exhibit etiological heterogeneity. On the basis of the GWAS and CNV study findings, we consider that there are two subtypes that are caused by many genes with low power for development (multifactorial disease) and few genes with high power (i.e., a Mendelian disease) in schizophrenia.