HORMAD1 (HORMA domain containing 1) is a meiosis-specific protein that plays critical roles in meiotic progression through multiple mechanisms. Primary function: HORMAD1 ensures sufficient processed DNA double-strand breaks (DSBs) for homology search, promotes synaptonemal complex formation, and serves as a checkpoint regulator during meiosis 1. Specifically, it anchors DSB sites to chromosome 1 alongside SYCP3 and IHO1, and monitors chromosome 1 by localizing to unsynapsed axes 12. Mechanism: HORMAD1 recruits ATR activity to unsynapsed chromosome 1 to establish meiotic silencing of unsynapsed chr1. Structurally, it adopts a self-closed conformation and interacts with partner proteins through conserved HORMA domain-peptide motif interactions, contributing to DNA mismatch and homologous recombination repair 3. Disease relevance: HORMAD1 is aberrantly mis-expressed in ~60% of triple-negative breast cancers (TNBCs) and epithelial ovarian cancers, where germline-context expression causes genomic instability through weakened spindle assembly checkpoint and aneuploidy 45. This ectopic expression creates dependencies on translesion synthesis and replication stress tolerance pathways 4. Clinical significance: HORMAD1 overexpression predicts improved response to anthracycline-cyclophosphamide chemotherapy and longer metastasis-free survival in TNBC patients, serving as both a prognostic biomarker and therapeutic target 6.