Of all the twins who share identical genes with a schizophrenia victim, about blank do not themselves develop schizophrenia

I believe that of all twins who share identical genes with a schizophrenia victim, about one-half do not themselves develop schizophrenia. Schizophrenia is a mental disorder that usually appears in late adolescence or early adulthood. Characterized by delusions, hallucinations, and other cognitive difficulties, schizophrenia can often be a lifelong struggle.