studies of the offspring of nonschizophrenic co-twins from discordant twin pairs suggest that . environmental factors play a more important role than genetic factors in the origin of schizophrenia genetic factors cause schizophrenia, while environmental factors are essentially unimportant a genetic predisposition to schizophrenia may remain unexpressed in some individuals unless it is released by some unknown environmental factors the heritability of schizophrenia involves the transmission of a single dominant gene