Abstract
This review analyses the genetic mechanisms of acephalic spermatozoa (AS) defects, which are associated with primary infertility in men. Several target genes of headless sperms have been identified but intracytoplasmic sperm injection (ICSI) outcomes are complex. Based on electron microscopic observations, broken points of the sperm neck are AS defects that are based on various genes that can be classified into three subtypes: HOOK1, SUN5, and PMFBP1 genes of subtype II; TSGA10 and BRDT genes of subgroup III, while the genetic mechanism(s) and aetiology of AS defects of subtype I have not been described and remain to be explored. Interestingly, all AS sperm of subtype II achieved better ICSI outcomes than other subtypes, resulting in clinical pregnancies and live births. For subtype III, the failure of clinical pregnancy can be explained by the defects of paternal centrioles that arrest embryonic development; for subtype I, this was due to a lack of a distal centriole. Consequently, the embryo quality and potential ICSI results of AS defects can be predicted by the subtypes of AS defects. However, this conclusion with regard to ICSI outcomes based on subtypes still needs further research, while the existence of quality of oocyte and implantation failure in women cannot be ignored.
Highlights
Of all infertility diseases in men, having acephalic spermatozoa (AS; OMIM: 617187) is one of the most serious male spermatogenic disorders that yields a unique abnormal sperm morphology: a large number of decapitated and decaudated spermatozoa with a small number of abnormal head-tail junction sperm in ejaculates [1, 2]
Separated heads and tails of sperm are commonly observed in both fertile and infertile population groups [4]. e limitation of specific management and a lack of knowledge of the pathogenesis make the clinical prognosis of AS defects unpredictable as these usually do not respond to pharmacological intervention [4,5,6]
Similar conditions can be observed within consanguinities and unrelated patients [4]. e ratio of headless to tailless sperm in semen is over 30 : 1 [7] since most of the heads are phagocytosed by Sertoli cells [4, 8, 9]
Summary
Of all infertility diseases in men, having acephalic spermatozoa (AS; OMIM: 617187) is one of the most serious male spermatogenic disorders that yields a unique abnormal sperm morphology: a large number of decapitated and decaudated spermatozoa with a small number of abnormal head-tail junction sperm in ejaculates [1, 2]. E separation in subtype II is located between the nucleus and proximal centriole: the lack of an implantation fossa and/or basal body in the tailless head, and the presence of intact proximal and distal centrioles in the headless tail have been reported [2, 10, 12, 27, 29]. It has been highlighted that c.340G > A variation in the SUN5 gene may affect the
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