HYDIN (axonemal central pair apparatus protein) is essential for ciliary and flagellar motility by maintaining the structural integrity of the axonemal central apparatus 1. HYDIN forms a semicircular chain that encircles the C1 and C2 microtubules within the sperm central apparatus, with its N-terminal half driving C1-C2 connection and C-terminal half providing axial support 1. Mutations in HYDIN cause primary ciliary dyskinesia (PCD), characterized by recurrent respiratory infections, sinusitis, bronchiectasis, and otitis media, typically without situs inversus totalis 2. Notably, HYDIN-mutant PCD patients often display normal ciliary ultrastructure on electron microscopy despite motility defects, distinguishing them from structural ciliary defects 23. Beyond respiratory manifestations, HYDIN loss-of-function inhibits GATA4 expression and enhances atrial septal defect risk in cardiac development 4. Additionally, HYDIN mutations are the fourth most common genetic cause of PCD in Indian populations 5, and HYDIN mutations in melanoma patients correlate with enhanced immune checkpoint inhibitor efficacy 6. Emerging evidence suggests HYDIN may also influence pain sensitivity through ciliary mechanisms in the choroid plexus-cerebrospinal fluid system 7.