Homozygous mutations inSPEF2induce multiple morphological abnormalities of the sperm flagella and male infertility

Abstract

BackgroundMale infertility due to multiple morphological abnormalities of the sperm flagella (MMAF) is a genetically heterogeneous disorder. Previous studies revealed several MMAF-associated genes, which account for approximately 60% of human MMAF cases. The pathogenic mechanisms of MMAF remain to be illuminated.Methods and resultsWe conducted genetic analyses using whole-exome sequencing in 50 Han Chinese probands with MMAF. Two homozygous stop-gain variants (c.910C>T (p.Arg304*) and c.3400delA (p.Ile1134Serfs*13)) of the SPEF2 (sperm flagellar 2) gene were identified in two unrelated consanguineous families. Consistently, an Iranian subject from another cohort also carried a homozygous SPEF2 stop-gain variant (c.3240delT (p.Phe1080Leufs*2)). All these variants affected the long SPEF2 transcripts that are expressed in the testis and encode the IFT20 (intraflagellar transport 20) binding domain, important for sperm tail development. Notably, previous animal studies reported spontaneous mutations of SPEF2 causing sperm tail defects in bulls and pigs. Our further functional studies using immunofluorescence assays showed the absence or a remarkably reduced staining of SPEF2 and of the MMAF-associated CFAP69 protein in the spermatozoa from SPEF2-affected subjects.ConclusionsWe identified SPEF2 as a novel gene for human MMAF across the populations. Functional analyses suggested that the deficiency of SPEF2 in the mutated subjects could alter the localisation of other axonemal proteins.

Biallelic mutations in Sperm flagellum 2 cause human multiple morphological abnormalities of the sperm flagella (MMAF) phenotype

“…Previous studies have promulgated the significance of SPEF2 in spermatogenesis . An intronic insertion within the Spef2 gene resulted in aberrant splicing and caused immotile and malformed sperm tails in pigs .…”

“…Many researchers have shown that the MMAF phenotype is associated with genetic mutations. Previous studies revealed that mutations in DNAH1 (MIM: 603332), DNAH2 (MIM: 603333), AKAP4 (MIM: 300185), CCDC39 (MIM: 613798), AK7 (MIM: 615364), CFAP251 (MIM: 618146), CEP135 (MIM: 611423), FSIP2 (MIM: 615796), ARMC2 (MIM: 611226), QRICH2 (MIM: 618304), SPEF2 (MIM: 610172), CFAP69 (MIM: 617949), CFAP43 (MIM: 617558) and CFAP44 (MIM:617559) could cause the human MMAF phenotype . However, more research is needed to reveal the etiology of the remaining 30%–40% of MMAF cases.…”

“…In the mouse model, nonsense mutations in the SPEF2 gene resulted in a primary ciliary dyskinesia (PCD)‐like phenotype that included sperm flagellar structure defects . Recently, there were also reports about SPEF2 mutations leading to the MMAF phenotype in humans . However, the role of SPEF2 in human disease needs to be confirmed, and its pathogenesis needs to be fully researched.…”

A novel homozygous CFAP65 mutation in humans causes male infertility with multiple morphological abnormalities of the sperm flagella

“…Since 2014, when MMAF was defined, studies have shown that mutations in genes associated with sperm flagellum development may lead to MMAF . Here, another candidate gene, CFAP65 , was identified in an infertile male with MMAF by WES.…”

“…The genetic basis of male infertility is still a work in progress, more than 4000 genes are expressed in germ cells during sperm production, and variations in these genes may hamper spermatogenesis . Recent studies of families with positive history related to male infertility have reported that mutations in cilia‐related genes are responsible for MMAF (eg, DNAH1 , CFAP43 , CFAP44 , CFAP69 , CFAP251 , QRICH2 , AK7 , CEP135 , FSIP2 , SPEF2 , TTC21A , ARMC2 , AKAP4 , CCDC39 ) . However, the known genetic defects can only explain ~60% of the individuals affected by MMAF …”