What is general level of concordance for twins and is it higher for monozygotic twins? What research is available on this?
The Wikipedia article seems to provide a summary of this information with links to the primary literature
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.
- 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.
You could check out the Meta-Analysis of Twin Correlations and Heritability (MATCH) website which is fully interactive and searchable.
The following image is a screenshot from their results on Schizophrenia, which shows that generally the concordance (here reported as correlation) of diagnosis between MZ twins is generally quite a bit higher than across DZ twins: