are less easily detected by microarrays than deletions. To exclude the possibility that the excess of de novos in cases reflects a lower sensitivity of the control platforms to detect duplications, we also examined the duplication/deletion ratios in the data sets. These were not significantly different (P>0.35 for each sample), although contrary to the hypothesis of a selective loss of sensitivity to detect duplications, both sets of controls actually had a higher proportion of duplications (Icelandic=0.39, Autism controls=0.36) than the cases (0.29). Further details on the size distribution of the de novo CNV are given in Supplementary Section 8, and of the full sensitivity analyses in Supplementary Section 1. Finally, we note that the control rates were similar to those in our experimental group with an affected parent (who according to an earlier work24 do not have elevated rates of de novo mutation), suggesting that technical variation between our own and other studies does not make a major impact on our conclusions.
