Novel mutations in ZMYND15 expand the phenotypic spectrum to acephalic spermatozoa: abnormal sperm head-tail connection mediated by SUN5.

Acephalic spermatozoa syndrome (ASS) is a rare cause of male infertility characterized by sperm tails lacking heads. Although zinc finger MYND-type containing 15 ( ZMYND15 ) mutations are linked to male infertility, their role in ASS is unknown. In this study, whole-exome sequencing identified novel homozygous truncating mutations, c.292C>T (p.Arg98Ter) and c.337G>T (p.Glu113Ter), in ZMYND15 from two infertile patients. These mutations caused protein truncation and impaired function, leading to extremely low sperm counts, poor motility, and numerous acephalic spermatozoa. Electron microscopy and sperm immunofluorescence revealed abnormal sperm neck structures, missing mitochondrial sheaths, failure of acrosome formation, and a lack of central microtubules. Experiments showed reduced mutant protein expression and high rates of degradation. Coimmunoprecipitation experiments indicated a direct interaction between ZMYND15 and Sad1 and UNC84 domain containing 5 (SUN5), crucial for forming the sperm head-tail connection. One patient achieved a live birth via intracytoplasmic sperm injection (ICSI), whereas the other had an early miscarriage. This study links ZMYND15 mutations directly to ASS, highlighting its role in spermatogenesis and offering insights for clinical diagnosis and treatment.