FIGURE 13.5 The Risk of Developing Schizophrenia Among Blood Relatives The risk percentages shown here reflect the collective results of about 40 studies investigating the likelihood of developing schizophrenia among blood relatives. As you can see, the greatest risk occurs if you have an identical twin who has schizophrenia (48 percent lifetime risk) or if both of your biological parents have schizophrenia (46 percent lifetime risk). However, environmental factors are also involved in the development of schizophrenia.
Source: Data from Gottesman (1991).