MLPA was carried out according to standard methods41 using reagents obtained from MRC-Holland (Amsterdam NL). The SALSA MLPA Kit P343-B1 Autism-1 probemix was used, which contained 9 probes within the deleted region on 16p11.2, plus one probe upstream and one downstream of this locus (see Figure 1a). MLPA products were separated using an AB3130 Genetic Analyser (Applied Biosystems) and outputs were analysed using GeneMarker software (Soft Genetics) and Microsoft Excel. Data normalisation was carried out by dividing the peak areas for each of the 11 test probes by the mean of 9 control probe peak areas. Normalised peak area data were then compared across the tested samples to determine which ones carried the 16p11.2 deletion.
