Pathogenic variants in MAEA disrupt DNA replication fork stability and are associated with developmental abnormalities in humans.

Replication stress (RS) poses a threat to genome stability and drives genomic rearrangements. The homologous recombination (HR) pathway repairs stalled replication forks (RFs) and prevents such instability. Through an E3 ubiquitin ligase screen aimed at identifying regulators of RAD51, we identified macrophage erythroblast attacher (MAEA), a core component of C-terminal to Lish (CTLH) E3 ubiquitin ligase complex, as a regulator of the HR pathway. Loss of MAEA impairs RAD51 recruitment at stalled RFs, leading to increased sensitivity to RS-inducing agents and excessive degradation of nascent DNA strands. Mechanistically, MAEA associates with and mediates the ubiquitylation of Ku80, enabling its removal from RF ends and facilitating the loading of RAD51. Notably, MAEA deficiency is associated with a developmental disorder involving microcephaly, craniofacial abnormalities, ocular defects, and heart malformations. Functional assays show that disease-linked MAEA variants (R34C, E349G, Y394D, and M396R) are defective in RS response. These findings establish MAEA as an essential factor in RF protection and genome integrity.