Monozygotic twins, folie à deux and heritability: a case report and critical review.

A case report of shared delusional disorder, with a primary diagnosis of delusional disorder, is described in identical twins of proven zygosity. A review of literature shows that the primary diagnosis in identical twin pairs, suffering from folie à deux, is delusional disorder. This is in contrast to the reported excess of schizophrenia, as a primary diagnosis, in non-twin cases of folie à deux. Moreover, schizophrenia is poorly related to delusional disorders on the basis of demographic and familial studies. In the light of this paradox, nosological status of this disorder and the sociogenic and genetic factors are critically discussed.