GMNN and Mungan syndrome: Meier-Gorlin syndrome (MGS) is caused by mutations in components of the prereplication and pre-initiation DNA replication complexes (ORC1, ORC4, ORC6, CDT1, CDC6, GMNN, CDC45), which license replication origins and mediate loading and functioning of the replication fork helicase (Bicknell et al. 2011; Burrage et al. 2015; Fenwick et al. 2016).