Findings from behavioral genetic studies are of particular importance to the present discussion because they provide evidence
that schizophrenia genes predispose their carriers not only to schizophrenia, but also to schizophrenia-like disorders, such as schizoaffective disorder and schizotypal personality disorder. These conditions are less severe than schizophrenia, but may be caused by the same genes,4 suggesting a spectrum of liability for schizophrenic illness. Consistent with this view, we proposed that genes involved in conferring liability Inhibitors,research,lifescience,medical for schizophrenia are a major etiological component of schizotaxia.11 Moreover, schizotaxia Inhibitors,research,lifescience,medical may be a ”truer“ expression of the genes that predispose to schizophrenic illness than is the diagnostic entity of schizophrenia itself, because the selleck compound latter condition may include less (etiologically) specific effects of psychosis.1,12 Environmental origins Despite the overwhelming evidence of a genetic influence in schizophrenia, it is clear that Inhibitors,research,lifescience,medical the presence of genes that confer liability for schizophrenia is not sufficient to cause the disorder in most cases. The case for environmental influence in schizophrenia/schizotaxia incorporates evidence from
several sources. First, the same behavioral genetic studies that show the importance of genetic Inhibitors,research,lifescience,medical factors in schizophrenic illness also underscore the importance of environmental variables. For example, in family studies,
no degree of biological relatedness, including the circumstance of having two schizophrenic parents, results in the development of schizophrenia 100% of the time. As described above, the liability in that case only approaches an average of 50%. Similarly, the risk of developing schizophrenia in a monozygotic (MZ) cotwin (who shares 100% of the Inhibitors,research,lifescience,medical other twin’s genes) whose sibling develops schizophrenia is also about 50%, which is far lower than would be predicted if genetic influence were the only etiologic factor. Consistent with such findings, Gottesman and Bertelsen13 showed that Terminal deoxynucleotidyl transferase rates of schizophrenia in the offspring of identical twins who were discordant for schizophrenia were equal. In all these examples, individuals who possessed the schizophrenia genotype did not necessarily express the disorder. Even the high estimates of heritability described above must be considered in context. Those studies showed that about 70% to 85% of the differences between people who develop schizophrenia and those who do not may be attributed to genetic factors (in the particular samples that were studied). Hiey did not mean that the overall influence of genetic factors is that high. Environmental influences encompass a variety of dimensions.