CCDC117 (coiled-coil domain containing 117) is a testis-enriched protein that functions as a negative regulator of testicular steroidogenesis. Primary Function: CCDC117 acts as a local brake on testosterone production in Leydig cells, maintaining appropriate androgen levels for reproductive homeostasis 1. Mechanism: CCDC117 deficiency triggers cell-autonomous upregulation of steroidogenic pathways in Leydig cells, resulting in compensatory hyperandrogenemia (approximately two-fold increase in serum testosterone and 1.5-fold elevation in intratesticular testosterone) independent of luteinizing hormone signaling 1. Disease Relevance: CCDC117 is a direct target of the cardiac transcription factor Nkx2.5 during outflow tract morphogenesis 2 and is dysregulated in various pathological contexts, including viral infection responses and metabolic diseases 34. Additionally, CCDC117 expression is regulated by miR-29b during early embryonic development, suggesting roles in developmental timing 5. Clinical Significance: CCDC117 knockout mice maintain normal spermatogenesis and near-normal fertility despite reduced testis size, revealing a compensatory mechanism ensuring reproductive resilience under structural compromise 1. These findings suggest CCDC117 represents a previously unrecognized local regulatory mechanism for male reproductive function.