Monozygotic twins schizophrenia

Schizophrenia is not a neurodegenerative disease but there is some general neuropathology. There is also evidence for a genetic influence. In monozygotic twins with... 

McNeil, T.F., Cantor-Graae, E., and Weinberger, D.R. (2000) Relationship of obstetric complications and differences in size of brain structures in monozygotic twin pairs discordant for schizophrenia. Am J Psychiatry 157 203-212. 

Environmental factors, such as prenatal maternal infections and perinatal complications, have been implicated in the pathogenesis of schizophrenia. Also, the correlation of only 0.6 for age of onset in monozygotic twins concordant for schizophrenia suggests that non-genetic factors play a role in determining the age of onset (Kendler et ah, 1987). A greater frequency or severity of these factors could conceivably result in an earlier onset of schizophrenia. 

There is an extensive literature showing that this disorder has a familial and hereditary pattern (42, 43, 44 and 45). Therefore, the genetic relatives of schizophrenic patients have an increased risk of developing this disorder. Several reviews of twin studies find that 30% to 65% of monozygotic twins are concordant for schizophrenia, in contrast to 0% to 28% of dizygotic twins (46, 47, 48, 49, 50, 51 and 52). 

There are also cross-fostering studies of children of schizophrenic parents, adopted away by nonschizophrenic foster parents, who were compared with adopted children of normal parents raised by schizophrenic foster parents ( 53, 54). Invariably, those children whose biological parents had schizophrenia developed this disorder more frequently than the offspring of nonschizophrenic parents, even when the latter were reared by schizophrenic foster families. In addition, the concordance rate for the illness in schizophrenic monozygotic twins reared apart was comparable with monozygotic twins reared together. These findings leave little doubt of a hereditary factor in schizophrenia. 

Belmaker R, Pollin W, Wyatt RJ, et al. Follow-up of monozygotic twins discordant for schizophrenia. Arch Gen Psychiatry 1974 30 219-222. 

Schizophrenia is a psychotic disorder of complex inheritance. The risk of developing the disorder is 1% in the general population but rises to 50% for monozygotic twins of an affected proband and approximately 10% for a sibling of a parent. 

Suddath, R., Christison, G., Torrey, E., Casanova, M., 8c Weinberger, D. (1990). Anatomical abnormalities in the brain of monozygotic twins discordant for schizophrenia. New England Journal of Medicine, 322, 789—794. 

Bartley AJ, Jones DW, Torrey EF, Zigun JR, Weinnberger DR. 1993. Sylvian fissure asymmetries in monozygotic twins A test of laterality in schizophrenia. Biol Psych 34 853-863. Beasley CL, Chana G, Honavar M, Landau S, Everall IP, et al. 2005. Evidence for altered neuronal organisation within the planum temporale in major psychiatric disorders. Schizophr Res 73(1) 69-78. 

Suddath RL, Christison GW, Torrey EF, Casanova MF, Weinberger DR. 1990. Anatomical abnormalities in the brains of monozygotic twins discordant for schizophrenia. NEJM... 

Weinberger, D. R., K. F. Berman, R. Suddath, and E. F. Torrey. 1992. Evidence of dysfunction of a prefrontal-limbic network in schizophrenia A magnetic resonance imaging and regional cerebral blood flow study of discordant monozygotic twins. American Journal of Psychiatry 149 890-97. 

Mata I, Madoz V, Arranz MJ, Sham P, Murray RM (2001) Olanzapine concordant response in monozygotic twins with schizophrenia. Br J Psychiatry 178 86... 

Twin research in schizophrenia presents us with puzzles. For example, although the usual quoted figure for concordance of schizophrenia in monozygotic (MZ) twins is approximately 50 percent, the classical modern study on the subject shows a variation of concordance of 31—58 percent depending on which Western country provides the statistics. The concordance rate in the United States, for example, is only 31 percent, while in the United Kingdom it s 58 percent.18 That is not a minor difference. 

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