Study question: Can whole-exome sequencing (WES) and in vitro validation studies identify new causative genes associated with teratozoospermia, particularly for sperm head defect?
Summary answer: We investigated a core group of infertile patients, including 82 cases with unexplained abnormal sperm head and 67 individuals with multiple morphological abnormalities of the sperm flagella (MMAF), and revealed rare and novel deleterious gene variants correlated with morphological abnormalities of the sperm head or tail defects.
What is known already: Teratozoospermia is one of the most common factors causing male infertility. Owing to high phenotypic variability, currently known genetic causes of teratozoospermia can only explain a rather minor component for patients with anomalous sperm-head shapes, and the agents responsible for atypical sperm head shapes remain largely unknown.
Study design, size, duration: We executed WES analysis of a Chinese cohort of patients (N = 149) with teratozoospermia to identify novel genetic causes particularly for defective sperm head. We also sought to reveal the influence of different abnormalities of sperm morphology on ICSI outcome.
Participants/materials, setting, methods: In this study, a cohort of 149 infertile men (82 with abnormal sperm head and 67 with MMAF) were recruited. We implemented WES on infertile patients and analyzed the negative effects of the mutations of candidate genes on their protein conformations and/or expression. We also investigated the candidate genes' spatiotemporal expression/localization during spermatogenesis in both humans and mice, and explored their interactions with proteins that are known to be involved in sperm development. We also compared the ICSI outcomes of the affected individuals with various aberrations in sperm morphology.
Main results and the role of chance: We identified rare and deleterious variants of piwi like RNA-mediated gene silencing 4 (PIWIL4: 1/82 patients, 1.21%), coiled-coil and C2 domain containing 1B (CC2D1B: 1/82 patients, 1.21%), cyclin B3 (CCNB3: 1/82 patients, 1.21%), KIAA1210 (KIAA1210: 2/82 patients, 2.43%) and choline phosphotransferase 1 (CHPT1: 1/82 patients, 1.21%), which are novel correlates of morphological abnormalities of the sperm head; functional evidence supports roles for all of these genes in sperm head formation. The mutations of septin 12 (SEPTIN12: 2/82 patients, 2.43%) are suggested to be associated with acrosome defects. We additionally observed novel causative mutations of dynein axonemal heavy chain 2 (DNAH2: 1/67 patients, 1.49%), dynein axonemal heavy chain 10 (DNAH10: 1/67 patients, 1.49%) and dynein axonemal heavy chain 12 (DNAH12: 1/67 patients, 1.49%) in patients with MMAF, and revealed a significantly lower fertilization rate of the abnormal sperm-head group compared to the MMAF group following ICSI. Consequently, our study also suggests that the mutations of PIWIL4 and CC2D1B might be circumvented by ICSI to a degree, and that CHPT1 and KIAA1210 loss-of-function variants might be associated with failed ICSI treatment.
Limitations, reasons for caution: In this study, we discovered the relationship between the genotype and phenotype of the novel causative genes of sperm head deformities in humans. However, the molecular mechanism of the relevant genes involved in sperm head development needs to be further illuminated in future research. Furthermore, evidence should be provided using knockout/knock-in mouse models for additional confirmation of the roles of these novel genes in spermatogenesis.
Wider implications of the findings: This cohort study of 149 Chinese infertile men documents novel genetic factors involved in teratozoospermia, particularly in anomalous sperm head formation. For the first time, we suggest that SEPTIN12 is related to human acrosomal hypoplasia, and that CCNB3 is a novel causative gene for globozoospermia in humans. We also uncovered variants in two genes-KIAA1210 and CHPT1associated with acrosomal biogenesis in patients with small or absent acrosomes. Additionally, it is postulated that loss-of-function mutations of PIWIL4 and CC2D1B have a contribution to the abnormal sperm-head formation. Furthermore, we are first to demonstrate the influence of different sperm morphologies on ICSI outcomes and indicates that the abnormal sperm head may play a significant role in fertilization failure. Our findings therefore provide valuable information for the diagnosis of teratozoospermia, particularly with respect to abnormalities of the sperm head. This will allow clinicians to adopt the optimal treatment strategy and to develop personalized medicine directly targeting these effects.
Study funding/competing interest(s): This work was financed by the West China Second University Hospital of Sichuan University (KS369 and KL042). The authors declare that they do not have any conflicts of interests.
Trial registration number: N/A.
Keywords: ICSI outcome; male infertility; morphological abnormalities of the sperm flagella; sperm head deformity; teratozoospermia; whole-exome sequencing.
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