Structural and Ultrastructural Assessment of the Sperm Annulus in Men with Immotile Short-tail Sperm Defects Compared to Normozoospermic Controls: A Case–control Study

Background: sperm annulus is a fibrous ring structure formed by septin proteins. It connects the mid-piece and principal piece of the sperm flagellum in mammals and plays a crucial role in flagellar stability and motility. Aim: This study aimed to compare the presence or absence of the sperm annulus in patients with immotile short-tail spermatozoa and a fertile control group. Settings and Design: This observational case-control study was conducted at a local research institute. Materials and Methods: Twenty infertile men with short-tail sperm defects (>50% of spermatozoa affected) and 20 fertile men with normal semen parameters were recruited. Immunocytochemistry was performed to assess the presence of the annulus using antibodies against Septin4 and Septin7. The absence of annular structures was confirmed by transmission electron microscopy (TEM). Statistical Analysis Used: No statistical analysis was performed in this study. Results: In the control group, Septin4 and Septin7 were precisely localised at the annulus region between the mid-piece and principal piece of spermatozoa. In contrast, spermatozoa from the patient group exhibited either a complete absence of annular staining or abnormal localisation of the annulus near the sperm head. In one patient, more than 90% of spermatozoa lacked Septin4 and Septin7 expression, as confirmed by TEM. Conclusion: Absence or structural abnormalities of the sperm annulus in men with short-tail spermatozoa may contribute to impaired motility. Evaluating annulus integrity may serve as a potential diagnostic biomarker in selected cases of male infertility.