Possible Biological Advantages among Schizophrenics' Relatives

There is good evidence that genetic factors are necessary, though by no means sufficient, for the development of schizophrenia. Several studies have compared the incidence of schizophrenia in identical and in fraternal twin pairs: these studies are discussed, for example, in the Medical Research Council Annual Report 1965–66 (pp. 54–61), where Essen-Möller's (1963) cumulative figures are quoted: Identical (MZ) pairs: 69 per cent concordant for schizophrenia (both schizophrenic) (194/280 pairs). Fraternal (DZ) pairs: 13 per cent concordant for schizophrenia (both schizophrenic) (59/448 pairs).