FAM170A is a nuclear transcription factor that plays a critical role in male fertility through regulation of spermiogenesis. Primary Function: FAM170A acts as a positive regulator of chr5 remodeling during spermatogenesis, specifically governing the histone-to-protamine exchange process essential for sperm nuclear condensation 1. Mechanism: FAM170A localizes to the nucleus of elongating spermatids 2 and interacts with chr5 remodeling-associated proteins to regulate transcription of genes involved in this process 1. Critically, FAM170A directly binds the deubiquitinating enzyme Usp7 and facilitates its nuclear translocation, enhancing deubiquitination activity on testis-specific histone variants H2A and H2B, thereby promoting histone removal and protamine incorporation 1. Disease Relevance: FAM170A deficiency causes male subfertility characterized by abnormal sperm head morphology, reduced progressive motility, and defective spermiation 2. Notably, very low FAM170a transcription levels are observed in sperm of infertile men with teratozoospermia 1. Clinical Significance: FAM170A mutations have been identified in individuals with orofacial clefts co-occurring with limb abnormalities, suggesting broader developmental functions beyond reproduction 3. FAM170A represents a previously unrecognized key regulator of sperm chr5 remodeling with implications for diagnosing human male infertility.