What is the concordance rate for schizophrenia in monozygotic and dizygotic twins?
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http://en.wikipedia.org/wiki/Causes_of_schizophrenia#Genetics


  Concordance rates between monozygotic twins vary in different studies,
  approximately 50%; whereas dizygotic twins was 17%. Some twin
  studies (Koskenvuo et al; Hoeffer et al) have found rates as low as 11.0%–13.8% among
  monozygotic twins, and 1.8%–4.1% among dizygotic twins, however.


References


Koskenvuo M, Langinvainio H, Kaprio J, Lönnqvist J, Tienari P; Langinvainio; Kaprio; Lönnqvist; Tienari (1984). "Psychiatric hospitalization in twins". Acta Genet Med Gemellol (Roma) 33 (2): 321–32. PMID 6540965.
Hoeffer A, Pollin W; Pollin (November 1970). "Schizophrenia in the NAS-NRC panel of 15,909 veteran twin pairs". Arch Gen Psychiatry 23 (5): 469–77. doi:10.1001/archpsyc.1970.01750050085012. PMID 5478575.