SPAG17 encodes a critical component of the central pair apparatus in motile cilia, essential for proper ciliary structure and function 1. The protein is required for sperm flagellum development and assembly of respiratory motile cilia central pair apparatus, but appears dispensable for brain ependymal cilia 1. SPAG17 plays a crucial role in male fertility, as homozygous mutations cause severe asthenozoospermia through multiple morphological abnormalities of spermatozoal flagella (MMAF), including incomplete C1a projections and missing microtubule doublets 23. Beyond reproductive function, SPAG17 regulates skeletal development and bone formation. Spag17-deficient mice exhibit skeletal malformations, altered limb patterning, and premature ossification, likely due to its role in primary cilia of chondrocytes and osteoblasts 4. Interestingly, SPAG17 also functions as a negative regulator of fibrosis - reduced expression in systemic sclerosis patients correlates with myofibroblast activation and skin fibrosis 5. Loss-of-function mutations cause primary ciliary dyskinesia with respiratory dysfunction and hydrocephalus in mice 1, while in humans they primarily manifest as male infertility that can be treated with ICSI and assisted oocyte activation 3.