Genomic DNA from a male proband, or in five instances a female obligate carrier, from 208 families with multiple individuals with mental retardation and a pattern of transmission compatible with X linkage (see Table 1 for clinical summary) was sequenced through the coding exons of 718 X-chromosome genes (Supplementary Table 1). This set was composed of 699 out of 829 genes from the Vega database and 19 X-chromosome genes not included in Vega but present in Ensembl/NCBI (Supplementary Table 1). The average coverage of the 718 genes screened was 75%; therefore, the coverage of the full protein-coding sequences of the Vega X chromosome was 65%. Sixteen of the genes screened are in the pseudoautosomal regions common to the X and Y chromosomes and 702 are in the X-specific part. The screened DNA corresponds to ~1 Mb of coding sequence per sample and >200 Mb in total. The 208 families were prescreened and found negative for cytogenetic abnormalities at 500G banding resolution, for expansion of the FMR1 trinucleotide repeat and for unambiguous disease-causing sequence variants in the XLMR-causing genes published when the study was initiated (Supplementary Table 1).
