Male infertility is a major concern affecting human reproductive health. Asthenoteratospermia can cause male infertility through reduced motility and abnormal morphology of spermatozoa. Several genes, including DNAH1 and some CFAP family members, are involved in multiple morphological abnormalities of the sperm flagella (MMAF). However, these known genes only account for approximately 60% of human MMAF cases. Here, we conducted further genetic analyses by using whole-exome sequencing in a cohort of 65 Han Chinese men with MMAF. Intriguingly, bi-allelic mutations of TTC21A (tetratricopeptide repeat domain 21A) were identified in three (5%) unrelated, MMAF-affected men, including two with homozygous stop-gain mutations and one with compound heterozygous mutations of TTC21A. Notably, these men consistently presented with MMAF and additional abnormalities of sperm head-tail conjunction. Furthermore, a homozygous TTC21A splicing mutation was identified in two Tunisian cases from an independent MMAF cohort. TTC21A is preferentially expressed in the testis and encodes an intraflagellar transport (IFT)-associated protein that possesses several tetratricopeptide repeat domains that perform functions crucial for ciliary function. To further investigate the potential roles of TTC21A in spermatogenesis, we generated Ttc21a mutant mice by using CRISPR-Cas9 technology and revealed sperm structural defects of the flagella and the connecting piece. Our consistent observations across human populations and in the mouse model strongly support the notion that bi-allelic mutations in TTC21A can induce asthenoteratospermia with defects of the sperm flagella and head-tail conjunction.

BackgroundMale infertility is a major issue of human reproduction health. Asthenoteratospermia can impair sperm motility and cause male infertility. Asthenoteratospermia with multiple morphological abnormalities of the flagella (MMAF) presents abnormal spermatozoa with absent, bent, coiled, short and/or irregular-calibre flagella. Previous studies on MMAF reported that genetic defects in cilia-related genes (eg, AKAP4, DNAH1, CFAP43, CFAP44 and CFAP69) are the major cause of MMAF. However, the known MMAF-associated genes are only responsible for approximately 30% to 50% of human cases. We further investigated the cases with MMAF in search of additional genes mutated in this condition.Methods and resultsWe conducted whole exome sequencing in a male individual with MMAF from a consanguineous Han Chinese family. Sanger sequencing was also conducted in additional individuals with MMAF. Intriguingly, a homozygous frameshift mutation (p.Leu357Hisfs*11) was identified in the gene encoding CFAP69 (cilia and flagella-associated protein 69), which is highly expressed in testis. The subsequent Sanger sequencing of the CFAP69 coding regions among 34 additional individuals with MMAF revealed a case with homozygous nonsense mutation (p.Trp216*) of CFAP69. Both of these CFAP69 loss-of-function mutations were not present in the human population genome data archived in the 1000 Genomes Project and ExAC databases, nor in 875 individuals of two Han Chinese control populations. Furthermore, we generated the knockout model in mouse orthologue Cfap69 using the CRISPR-Cas9 technology. Remarkably, male Cfap69-knockout mice manifested with MMAF phenotypes.ConclusionOur experimental findings elucidate that homozygous loss-of-function mutations in CFAP69 can lead to asthenoteratospermia with MMAF in humans and mice.

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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.

As a type of severe asthenoteratospermia, multiple morphological abnormalities of the flagella (MMAF) are characterized by the presence of immotile spermatozoa with severe flagellar malformations. MMAF is a genetically heterogeneous disorder, and the known MMAFassociated genes can only account for approximately 60% of human MMAF cases. Here we conducted whole-exome sequencing and identified bi-allelic truncating mutations of the TTC29 (tetratricopeptide repeat domain 29) gene in three (3.8%) unrelated cases from a cohort of 80 MMAF-affected Han Chinese men. TTC29 is preferentially expressed in the testis, and TTC29 protein contains the tetratricopeptide repeat domains that play an important role in cilia-and flagella-associated functions. All of the men harboring TTC29 mutations presented a typical MMAF phenotype and dramatic disorganization in axonemal and/or other peri-axonemal structures. Immunofluorescence assays of spermatozoa from men harboring TTC29 mutations showed deficiency of TTC29 and remarkably reduced staining of intraflagellar-transport-complex-B-associated proteins (TTC30A and IFT52). We also generated a Ttc29-mutated mouse model through the use of CRISPR-Cas9 technology. Remarkably, Ttc29-mutated male mice also presented reduced sperm motility, abnormal flagellar ultrastructure, and male subfertility. Furthermore, intracytoplasmic sperm injections performed for Ttc29-mutated mice and men harboring TTC29 mutations consistently acquired satisfactory outcomes. Collectively, our experimental observations in humans and mice suggest that bi-allelic mutations in TTC29, as an important genetic pathogeny, can induce MMAF-related asthenoteratospermia. Our study also provided effective guidance for clinical diagnosis and assisted reproduction treatments.

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Asthenoteratozoospermia characterized by multiple morphological abnormalities of the flagella (MMAF) has been identified as a sub-type of male infertility. Recent progress has identified several MMAF-associated genes with an autosomal recessive inheritance in human affected individuals, but the etiology in approximately 40% of affected individuals remains unknown. Here, we conducted whole-exome sequencing (WES) and identified hemizygous missense variants in the X-linked CFAP47 in three unrelated Chinese individuals with MMAF. These three CFAP47 variants were absent in human control population genome databases and were predicted to be deleterious by multiple bioinformatic tools. CFAP47 encodes a cilia-and flagella-associated protein that is highly expressed in testis. Immunoblotting and immunofluorescence assays revealed obviously reduced levels of CFAP47 in spermatozoa from all three men harboring deleterious missense variants of CFAP47. Furthermore, WES data from an additional cohort of severe asthenoteratozoospermic men originating from Australia permitted the identification of a hemizygous Xp21.1 deletion removing the entire CFAP47 gene. All men harboring hemizygous CFAP47 variants displayed typical MMAF phenotypes. We also generated a Cfap47-mutated mouse model, the adult males of which were sterile and presented with reduced sperm motility and abnormal flagellar morphology and movement. However, fertility could be rescued by the use of intra-cytoplasmic sperm injections (ICSIs). Altogether, our experimental observations in humans and mice demonstrate that hemizygous mutations in CFAP47 can induce X-linked MMAF and asthenoteratozoospermia, for which good ICSI prognosis is suggested. These findings will provide important guidance for genetic counseling and assisted reproduction treatments.

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