No abstract

In the Provincial sample, the prevalence of "spectrum" disorders was significantly greater in biological relatives of schizophrenia spectrum vs control adoptees. The results were also consistent with the genetic transmission of individual diagnoses within the spectrum. When combined into the National sample, the results provided strong evidence for (1) the genetic transmission of DSM-III schizophrenia; (2) a genetic relationship between DSM-III schizophrenia, mainly schizophrenic schizoaffective disorder, and schizotypal personality disorder; and (3) the absence of a significant genetic relationship between the schizophrenia spectrum and either psychotic nonspectrum disorders, major depression, or anxiety disorders. We found no evidence for the familial environment transmission of schizophrenia spectrum disorders. These results are consistent with the findings reported by Kety and coworkers from their diagnostic review.

"Schizotypy" is a complex, multidimensional clinical construct, whose various dimensions differ widely both in the degree and specificity with which they reflect the familial liability to schizophrenia. Subpsychotic thought disorder; negative schizotypal signs, such as poor rapport and odd behavior; deficient occupational functioning; and social isolation/avoidance best characterized relatives of schizophrenic probands compared with relatives of matched controls.

These results support the following hypotheses: (1) in the West of Ireland, as in other populations, schizophrenia is a strongly familial disorder; (2) schizophrenia shares a familial predisposition with a spectrum of clinical syndromes that includes schizoaffective disorder, other nonaffective psychoses, schizotypal personality disorder, and probably psychotic AI, but not nonpsychotic AI; and (3) the diminished reproductive rates associated with schizophrenia have a large impact on the pattern of risk of illness in relatives.