Deep sequencing reveals variations in somatic cell mosaic mutations between monozygotic twins with discordant psychiatric disease

Monozygotic (MZ) twins have been thought to be genetically identical. However, recent studies have shown discordant variants between them. We performed whole-exome sequencing (WES) in five MZ twin pairs with discordant neurodevelopmental disorders and one healthy control MZ twin to detect discordant variants. We identified three discordant variants confirmed by deep sequencing after analysis by personalized next-generation sequencing (NGS). Three mutations in FBXO38 (chr5:147774428;T>G), SMOC2 (chr6:169051385;A>G) and TDRP (chr8:442616;A>G), were detected with low allele frequency of mutant alleles on deep sequencing, suggesting that these loci are mosaic due to somatic mutations in a developmental stage. Our results suggest that deep sequencing analysis would be an adequate method to detect discordant mutations in candidate genes responsible for heritable diseases.