a DNA damage responsive protein and transcriptional repressor of human telomere reverse transcriptase. An early responder to DNA damage. Required for double strand break repair via homologous recombination and nonhomologous end joining. Promotes chromatin relaxation by recruiting and maintaining the chromatin remodeling SWI-SNF complex at sites of DNA double strand breakage. Participates in the ATR/Chk1-mediated DNA checkpoint in humans and transcriptionally regulates BRCA1 and Chk1. Plays a role in neurogenesis and regulation of the size of the cerebral cortex. Mutations of MCPH1 can cause microcephaly in humans and appears to play an evolutionarily conserved role in brain development. Alterations have been identified in breast, ovarian and prostate cancer. Appears to coordinate S-M transitions in fly embryos. Note: This description may include information from UniProtKB.