ARMCX4 is an X-linked armadillo repeat-containing protein belonging to the GPRASP/ARMCX family, which comprises 10 proteins with conserved armadillo-like repeats in their carboxy-terminal regions 1. ARMCX4 is classified within subfamily 1 of this family, characterized by additional repeated motifs distinct from subfamily 2 members that possess mitochondrial targeting domains 1. Functionally, ARMCX4 knockdown in mouse spermatogonial stem cells represses their differentiation in vitro, suggesting a role in regulating spermatogenesis 2. Low-frequency variants in ARMCX4 have been identified in association with male infertility in exome sequencing studies 2. In disease contexts, ARMCX4 was identified as a hub gene in non-STEMI (non-ST-elevation myocardial infarction) patients, where it associates with extracellular space and calcium-binding functions in platelet transcriptomes 3. Additionally, ARMCX4 was identified as a potential passenger gene in endometrial cancer patients 4. While the precise molecular mechanisms remain incompletely understood, ARMCX4 appears involved in reproductive development and cardiovascular pathophysiology, potentially through interactions with cellular trafficking and signaling pathways characteristic of the GPRASP/ARMCX protein family 1.