ORC4 and Meier-Gorlin syndrome: Several other DNA replication complex genes have also been identified as causative in Meier-Gorlin syndrome, including ORC1, ORC4, ORC6, CDT1, CDC6 and CDC45, members of the pre-replication (pre-RC) and pre-initiation (pre-IC) complexes, as well as GMNN, a regulator of cell-cycle progression and DNA replication [40].