Gene interaction in the phenotypic expression of mental diseases

A genealogical analysis is carried out on the pedigrees of 10 twin pairs with two or more psychoses. The probands' symptoms reveal some peculiar aspects, i.e., an atypical phenomenology possibly due to the interference of more pathological genes. Schizophrenia, depression, epilepsy, and obsessive neurosis, are found in the pedigrees in different combinations. The study of these pedigrees would lead to the conclusion that interaction of more than one psychosis gives rise to atypical forms as a result of an attempt to establish a state of balance between opposing dynamic actions, as in reversible chemical reactions. Probands' symptoms are less severe and with an often more favourable prognosis. Epilepsy tends to become independent and the major psychoses seem to be epistatic on it. As for obsessive-compulsive neurosis, probands may progress into schizophrenia or depression if one of these psychoses is present in the pedigree, or may represent the neurotic form of the major disease.