There are numerous monogenic neurodevelopmental disorders, including 22q11DS, Snijders Blok-Campeau syndrome (CDH3) and KBG syndrome (ANKRD11), with reports of discordant monozygotic twins and/or variable expressivity across individuals in families who inherit the same pathogenic sequence variant [49–51]. Here, CDH3 is linked to 22q11.2 deletion syndrome.