IN THE ATTEMPT to understand why schizophrenic symptoms appear in one individual and not in another, major investigative efforts have been directed toward: (1) assessing the genetic component which controls the cellular and physiologic characteristics of the central nervous system, thereby influencing what is called temperament, nervous disposition, personality, or mind; (2) assessing the environmental experiential factors which temper the degree of development and expression of the personality; or (3) the complex interaction of endowment and environment.
The study of pairs of monozygotic twins, when one twin has developed schizophrenic symptomatology and the other has not, has the unique research power of controlling for the genetic differences which occur between siblings and randomly selected individuals. Differences in environmental experience from the intra-uterine period through the onset of illness are therefore highlighted in these pairs.
Characteristics of an infant at birth, the classically designated time for the "begin
Stabenau JR, Pollin W. Early Characteristics of Monozygotic Twins Discordant for Schizophrenia. Arch Gen Psychiatry. 1967;17(6):723-734. doi:10.1001/archpsyc.1967.01730300083011