Acephalic spermatozoa syndrome is a severe teratozoospermia that leads to male infertility. Our previous work showed that biallelic SUN5 mutations are responsible for acephalic spermatozoa syndrome in about half of affected individuals, while pathogenic mechanisms in the other individuals remain to be elucidated. Here, we identified a homozygous nonsense mutation in the testis-specific gene PMFBP1 using whole-exome sequencing in a consanguineous family with two infertile brothers with acephalic spermatozoa syndrome. Sanger sequencing of PMFBP1 in ten additional infertile men with acephalic spermatozoa syndrome and without SUN5 mutations revealed two homozygous variants and one compound heterozygous variant. The disruption of Pmfbp1 in male mice led to infertility due to the production of acephalic spermatozoa and the disruption of PMFBP1's cooperation with SUN5 and SPATA6, which plays a role in connecting sperm head to the tail. PMFBP1 mutation-associated male infertility could be successfully overcome by intracytoplasmic sperm injection (ICSI) in both mouse and human. Thus, mutations in PMFBP1 are an important cause of infertility in men with acephalic spermatozoa syndrome.

Acephalic spermatozoa syndrome is a rare and severe form of teratozoospermia characterized by a predominance of headless spermatozoa in the ejaculate. Family clustering and consanguinity suggest a genetic origin; however, causative mutations have yet to be identified. We performed whole-exome sequencing in two unrelated infertile men and subsequent variant filtering identified one homozygous (c.824C>T [p.Thr275Met]) and one compound heterozygous (c.1006C>T [p.Arg356Cys] and c.485T>A [p.Met162Lys]) SUN5 (also named TSARG4) variants. Sanger sequencing of SUN5 in 15 additional unrelated infertile men revealed four compound heterozygous (c.381delA [p.Val128Serfs7] and c.824C>T [p.Thr275Met]; c.381delA [p.Val128Serfs7] and c.781G>A [p.Val261Met]; c.216G>A [p.Trp72] and c.1043A>T [p.Asn348Ile]; c.425+1G>A/c.1043A>T [p.Asn348Ile]) and two homozygous (c.851C>G [p.Ser284]; c.350G>A [p.Gly114Arg]) variants in six individuals. These 10 SUN5 variants were found in 8 of 17 unrelated men, explaining the genetic defect in 47.06% of the affected individuals in our cohort. These variants were absent in 100 fertile population-matched control individuals. SUN5 variants lead to absent, significantly reduced, or truncated SUN5, and certain variants altered SUN5 distribution in the head-tail junction of the sperm. In summary, these results demonstrate that biallelic SUN5 mutations cause male infertility due to autosomal-recessive acephalic spermatozoa syndrome.

SUN (Sad1 and UNC84 domain containing)-domain proteins are reported to reside on the nuclear membrane playing distinct roles in nuclear dynamics. SUN5 is a new member of the SUN family, with little knowledge regarding its function. Here, we generated Sun5−/− mice and found that male mice were infertile. Most Sun5-null spermatozoa displayed a globozoospermia-like phenotype but they were actually acephalic spermatozoa. Additional studies revealed that SUN5 was located in the neck of the spermatozoa, anchoring sperm head to the tail, and without functional SUN5 the sperm head to tail coupling apparatus was detached from nucleus during spermatid elongation. Finally, we found that healthy heterozygous offspring could be obtained via intracytoplasmic injection of Sun5-mutated sperm heads for both male mice and patients. Our studies reveal the essential role of SUN5 in anchoring sperm head to the tail and provide a promising way to treat this kind of acephalic spermatozoa-associated male infertility.