Abstract
The diagnostic boundaries of schizophrenia remain controversial. Although there may be little disagreement about classifying process schizophrenia as schizophrenia, the inclusion of good-prognosis schizophrenia,1 borderline syndromes, or nonpsychotic conditions has engendered more debate. The issue regarding good-prognosis schizophrenia has been clarified by a number of studies2–6 indicating that this group has clinical and family differences from process schizophrenia. Progress in classifying borderline syndromes and nonpsychotic conditions has not been as great. As we have previously stated,7 the reasons seem to be difficulty in defining these disorders as well as a lack of data regarding their occurrence in the general population.
Because of this impasse, we have looked for indirect ways of defining the boundaries of schizophrenia. One approach has been to compare positive family history schizophrenics with negative family history schizophrenics on the assumption that schizophrenics with a loaded family history for process schizophrenia should also have a loaded family history for other disorders that are related to schizophrenia. The frequency of other psychiatric disorders in these two groups were not significantly different;8 thus failing to support the extension of the concept of schizophrenia to include such nonpsychotic conditions as neuroses or personality disorder.
Because there is a positive association between schizophrenia in the siblings of schizophrenics and parental schizophrenia,9 the present report makes the following assumption: If there are borderline or nonpsychotic psychiatric illnesses that are genetically related to schizophrenia, their occurrence in parents should be associated with schizophrenia in the siblings of schizophrenics. Conversely, if there are parental illnesses that are distinct from schizophrenia, they should be associated with other illnesses in the siblings because most mental disorders, regardless of their etiology, have been shown to run in families.