Novel variants of FSIP2 and SPEF2 cause varying degrees of spermatozoa damage in MMAF patients and favorable ART outcomes.

Purpose: This study identified novel variants of the FSIP2 and SPEF2 genes in multiple morphological abnormalities of the sperm flagella (MMAF) patients and to investigate the potential effect of variations on male infertility and assisted reproductive outcomes.

Methods: Whole-exome sequencing was performed in 106 Chinese MMAF patients. The discovered variants were evaluated in silico and confirmed by Sanger sequencing. A mini-gene assay and immunofluorescence staining were used to determine the effects on mRNA and protein. Assisted reproductive technology (ART) based on intracytoplasmic sperm injection (ICSI) and in vitro fertilization (IVF) was used for MMAF patients carrying novel variants.

Results: Biallelic variants in FSIP2 or SPEF2 involving nineteen novel variations were found in eleven MMAF patients. These variations included fourteen missense variants, two nonsense variants, two frameshift variants, and a splicing variant. The FSIP2 protein was markedly reduced or mislocalized to the spermatozoa head. Two novel missense variants of SPEF2 reduced cell diameter. Eleven MMAF couples had 12 ICSI cycles and 2 IVF cycles. The 2PN fertilization rate, good-quality embryos rate, and clinical pregnancy rate were 80.1% (133/166), 74.4% (99/133), and 45.7% (16/35). Four of them have seven babies born.

Conclusion: Our work revealed that missense variations of FSIP2 or SPEF2 might cause a milder spermatozoa damage. The infertility caused by FSIP2 and SPEF2 variants can be mitigated through ICSI or even IVF. The results of this study presented signs of the correlation of phenotype/genotype for the FSIP2 and SPEF2, which might provide a reference for clinical genetic and fertility consultation.