It is apparent that the genetic vulnerability to schizophrenia is not only expressed as schizophrenia. These findings are

in keeping with those of another series of family studies, which showed that all variants of nonaffectivc find more psychotic disorders (schizotypal personality disorders and schizoaffective disorders) cosegregated with schizophrenia.13 Table II. Lifetime prevalences in relatives of schizophrenics (obligate carriers) and controls. Inhibitors,research,lifescience,medical *P≤0.05. Similarly, some family studies reported an excess of affective disorders (particularly psychotic affective disorders) in subjects at elevated risk for schizophrenia. In addition, one series of family studies12 demonstrated that a heterogeneous collection of deviations (eg, personality deviations not qualifying as a disorder, neuropsychological deficits) might also develop as Inhibitors,research,lifescience,medical a consequence of an increased risk for schizophrenia. Thus, the range of the phenotype transmitted in families of schizophrenics is not at all identical to the diagnostic boundaries proposed by any diagnostic manual. On the other hand, there is also Inhibitors,research,lifescience,medical evidence that specific subtypes of schizophrenia aggregate in families with a very specific pattern of aggregation. Recently, Beckmann et al14 demonstrated

that periodic catatonia defined a homogeneous familial aggregation pattern. However, this specific psychotic syndrome is only remotely associated with the catatonic subtype of schizophrenia defined by ICD-10 and Inhibitors,research,lifescience,medical DSM-III-R. Taken together, the diagnostic distinctions and boundaries defined by ICD-10 and DSM-III-R are not compatible with the phenotype of schizophrenia transmitted in families, although these diagnostic categories were shown to be familial and under genetic control. Diagnostic definitions and linkage studies Consequently, it is not surprising that linkage studies tracing the localization of susceptibility genes for a specific psychiatric disorder have failed to reveal a specific relationship to diagnostic categories. Two examples of this are discussed in the following. One replicated

linkage finding in Inhibitors,research,lifescience,medical schizophrenia is on 6p.15 Maximal logarithm of the odds of linkage (LOD) scores indicate the strength of cosegregation of genetic markers and the disease. Comparison of the maximal LOD scores across diagnosticdefinitions (by DSM-III-R), varying Mephenoxalone by restrictiveness, revealed maximal diagnosis-specific LOD scores for the broadest definition including all variants of psychotic disorders; the maximal LOD score for narrowly defined schizophrenia was substantially lower. Several candidate regions in the genome are likely to host susceptibility genes for bipolar affective disorders. One of these regions is 18p. A suggested linkage to bipolar disorder was found by several independent linkage studies in bipolar disorder. Recently, Schwab et al16 also found suggested linkage for schizophrenia to the same pericentromeric candidate region.