Homozygous Myo7A mutation associations teratozoospermia and intracytoplasmic sperm injection failure in humans and mice.

BACKGROUND

Teratozoospermia, characterized by a high proportion of morphologically abnormal sperm, severely impairs male fertility. This study focused on an infertile male patient presenting with globozoospermia and multiple morphological abnormalities of the flagella (MMAF), with the aim of uncovering the etiology of teratozoospermia.

METHODS

An infertile male patient presenting with globozoospermia and MMAF was enrolled in this study. Whole-exome sequencing (WES) was performed to screen for potential pathogenic genetic variants associated with teratozoospermia. Immunofluorescence (IF) staining was subsequently employed to examine the expression patterns. Subsequently, IF staining was conducted to evaluate the expression patterns of unconventional myosin VIIa (Myo7a) and assess acrosome integrity in sperm cells. Additionally, western blot (WB) and co-immunoprecipitation (Co-IP) were adopted to investigate potential molecular disruptions in spermatogenesis pathways. Finally, intracytoplasmic sperm injection (ICSI) and artificial oocyte activation (AOA) were performed, followed by embryo transfer to evaluate the efficacy of assisted reproductive technology in this specific pathological context.

RESULTS

Genetic screening via WES identified a homozygous Myo7a variant (c.617G>A; p.R206H) in the patient. IF analysis demonstrated complete an absence of Myo7a protein expression in the patient's spermatozoa, which was concurrent with the loss of acrosomal structure. Comparative assessment revealed conserved cytoplasmic and flagellar localization patterns of Myo7a during spermatid development in both mice and human testicular tissues. Quantification of sperm development markers showed significant reduction in expression levels of DPY19L2, FSIP2, DNAH8, and DNAH17 proteins compared to controls. In the first in vitro fertilisation (IVF) cycle, none of the eggs were fertilised. In the second ICSI cycle, low fertilisation rate followed by embryo transfer failed to establish clinical pregnancy. In the third ICSI + AOA cycle, a clinical pregnancy was achieved.

CONCLUSIONS

Our findings indicate that Myo7a gene defects affect sperm function by combining dysregulation of key structural proteins such as DPY19L2, FSIP2, DNAH8 and DNAH17. Fertilisation disorders caused by Myo7a can be overcome by AOA + ICSI. The study provides novel insights into the role of Myo7a during sperm development across species and advances the understanding of teratozoospermia mechanisms.