Concordance rates in monozygotic and dizygotic twin pairs classified by their sex. ASD concordance rates are higher for monozygotic than dizygotic twins, and concordance in dizygotic twins shows an effect of sex. (A) Mosaic plot shows the proportion of concordant monozygotic (MZ) twin pairs by the sex of the pair (F-F = female-female, M-M = male-male). Mosaic plots in (B), (C), and (D) show recurrence rates for ASD in co-twins from dizygotic (DZ) twin pairs by co-twin sex (B), proband twin sex (C), and by each combination of proband and co-twin sex (D). Bar widths are proportional to the number of twin pairs in each group, which is also noted in the figure, and whiskers note the 95% confidence intervals around each recurrence risk estimate. Relative risk (RR) and P values for each comparison of interest are also noted in the figure.