suspiciousness, paranoid personality, and delusional disorder,
compared with relatives of control subjects; however,
the families have no increase in schizophrenia or mood disorders
(8,9). Also, cases of schizophrenia-spectrum disorders
were found to be strongly concentrated in the biological relatives
of adoptees with schizophrenia. However, this pattern
was not found for delusional disorder, suggesting that, from a
genetic perspective, delusional disorder is not part of the
schizophrenia spectrum. Despite these early and preliminary
studies, the genetic associations between delusional disorder
and paranoid schizophrenia remain enigmatic. Nevertheless,
the strongest hypothesis holds that the entity of delusional disorder
is one possible source of the heterogeneity within
“schizophrenia” (10).