Gottesman and Shields A review of recent adoption twin and family studies of schizophrenia
Aim... To review research on genetic transmission of schizophrenia.
Methodology... A review of adoption and twin studies into schizophrenia between 1967 and 1976. Studies reviewed: - Three adoption studies. - Five twin studies. In total there were 711 participants in the adoption studies. In the twin studies a total of 210 monozygotic (identical) twin pairs and 319 dizygotic (non-identical) twin pairs were studied.
Procedure... The incidence of schizophrenia in adopted children and monozygotic twins was extrapolated from the research. This was done by comparing biological parents and siblings and adoptive parents and siblings in the adoption studies. In the twin studies the concordance rates (how often both twins were diagnosed with schizophrenia) for monozygotic and dizygotic twins were compared.
Findings... All three adoption studies found an increased incidence of schizophrenia in adopted children with a schizophrenic biological parent, whereas normal children fostered to schizophrenic parents and adoptive parents of schizophrenic children showed little evidence of schizophrenia. One of the studies by Kety (1975) found that biological siblings of children with schizophrenia showed a much higher percentage of schizophrenia (19.2%) compared with adoptive siblings (6.3%).
Continued... All twins studies found a higher concordance rate of schizophrenia in monozygotic twins than dizygotic twins. In Gottesman and Shields’ own study (1972) this was 58% in monozygotic twins, meaning that if one twin had schizophrenia then there was a 58% chance the other would have it, compared with a 12% concordance rate for dizygotic twins.
Conclusions... There is obviously a significant genetic input to the onset of schizophrenia, but with concordance rates less than 100% there must be some interaction with the environment. There is also some confusion as to whether one or many genes are responsible for predisposing schizophrenia. 58% nature – 48% nurture.