Tetrachoric correlations and concordance rates of rheumatoid arthritis in Danish twins according to zygosity and ACPA status.

Values in parenthesis are 95% confidence intervals. ACPA denotes anti-citrullinated peptides antibody-positive rheumatoid arthritis. MZ denotes monozygotic, DZss dizygotic same sexed, and DZos dizygotic opposite sexed.
*There was one secondary case among the MZ concordant pairs, three among the DZ concordant pairs and one among the DZos pairs.
$The estimates of the casewise concordance of MZ and DZss twins are adjusted for sex.