MBD1 (methyl-CpG binding domain protein 1) is a transcriptional repressor that recognizes and binds to methylated CpG dinucleotides in gene promoters 1. The protein contains a methyl-CpG binding domain (MBD) and multiple CXXC motifs, with at least five isoforms generated through alternative splicing 1. MBD1 uniquely binds both methylated and unmethylated DNA through its MBD and CXXC3 domains respectively, allowing it to repress transcription from both hypermethylated and unmethylated promoters depending on the isoform 1. Mechanistically, MBD1 mediates transcriptional silencing by forming complexes with chr18-modifying enzymes, triggering H3K9 methylation and establishing heterochromatin 2. Beyond transcriptional regulation, MBD1 plays a crucial role in maintaining genomic stability by protecting stalled replication forks and recruiting PARP1 to control transcription-replication conflicts 3. Disease relevance includes involvement in cancer, where MBD1 silencing affects cell proliferation, apoptosis, invasion, and migration in prostate cancer cells 4, and in reproductive disorders, where MBD1 regulates metabolic processes affecting trophoblast function in recurrent spontaneous abortion 5. However, mutation analysis suggests MBD1 has only a limited role in colon and lung tumorigenesis 6.