Accurate acrosome formation and flagellum assembly during spermiogenesis are important prerequisites to ensure the fertilization of sperm and eggs. However, no spermiogenesis related gene mutation was reported to directly result in disorders of acrosome formation and flagellum assembly. In this manuscript, by whole exome sequencing of 47 individuals with severe asthenozoospermia from 45 unrelated Chinese families, Tan et al. described their findings of bi-allelic CFAP65 mutations in 3 individuals from 3 unrelated families with completely immotile spermatozoa. CFAP65 could localize at the acrosome region and the flagellar midpiece of spermatozoa, whose deletion caused both sperm flagellar abnormalities and acrosomal hypoplasia. Intracytoplasmic sperm injection with CFAP65 mutant spermatozoa has poor clinical outcome. This study revealed a new gene involved in both acrosomal development and flagellum assembly, and this finding may also have important clinical implications for genetic and reproductive counseling of affected families. (By Dr. Yue-Qiu Tan, https://jmg.bmj.com/content/early/2019/08/14/jmedgenet-2019-106031 )