3. No additional serious pathogenic mutations on the X-chromosomes were detected in I2 by exome sequencing
Since MECP2 duplication in I2 might be on the active X-chromosome, we hypothesized the presence of an additional more serious pathogenic mutation on the other X-chromosome that would be responsible for skewing. As Affymetrix CytoScan HD Array detected no other likely harmful copy number variations in I2 but not in II2. Then we performed exome sequencing on DNA for females I2 and II2, we screened the mutations of genes in the OMIM catalog and found some that existed in I2 but not in II2. There were 12 mutations on the X-chromosomes, including one nonsense mutation and 11 missense mutations. Only three genes (NROB1 , DMD, and USP9X ) were involved in diseases, but there was no evidence to show that the three missense gene mutations were pathogenic (data not shown).