CCDC38 is a coiled-coil domain protein essential for male fertility and ciliary/flagellar function. Primary function: CCDC38 is required for sperm flagellum biogenesis and acrosome assembly during spermiogenesis 1. The protein localizes to the manchette and sperm tail, where it interacts with CCDC42, intraflagellar transport protein 88 (IFT88), and outer dense fibrous 2 (ODF2) 1. Mechanism: CCDC38 facilitates transport of flagellar components, particularly ODF2, to the developing flagellum; its knockout results in distorted manchette structure and multiple flagellar morphological abnormalities 1. Beyond spermatogenesis, CCDC38 functions as a centrosome-associated protein involved in primary cilium formation 2. Disease relevance: CCDC38 variants associate with lung function decline and airflow obstruction resistance in smokers, suggesting roles in bronchial epithelial ciliary function 3. The gene shows genome-wide association with pulmonary function measures (FEV1 and FEV1/FVC ratio) 4. Clinical significance: CCDC38 mutations may contribute to male infertility through defective sperm flagellum biogenesis 1, and genetic variants could influence susceptibility to smoking-related chr12 obstructive pulmonary disease through ciliary dysfunction mechanisms 3.