All of the following statements about the genetic basis of schizophrenia are trueEXCEPT that
A ) adoption studies indicate a biological basis for schizophrenia.
B ) the concordance rate for schizophrenia is higher for monozygotic than for dizygotic twins.
C ) a person with a “schizophrenia gene” will always develop schizophrenia.
D ) several genes may be involved in schizophrenia.
E ) genes impart a susceptibility to develop schizophrenia.