Bi-allelic Mutations in TTC21A Induce Asthenoteratospermia in Humans and Mice

Abstract

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.

Whole exome sequencing of men with multiple morphological abnormalities of the sperm flagella reveals novel homozygous QRICH2 mutations

“…The genetic characterization of this phenotype began in 2014 with the identification of DNAH1 (dynein axonemal heavy chain 1) as a major gene implicated in MMAF . After the development and the introduction of high throughput sequencing (HTS) techniques such as whole exome sequencing (WES), deleterious mutations were formally identified in eight additional MMAF genes ( AK7 , ARMC2 , CFAP43 , CFAP44 , CFAP69 , FSIP2 , TTC21A , and WDR66 ) showing the high genetic heterogeneity of this phenotype. Despite these important advances in gene identification, about half of the MMAF cases remain idiopathic without a genetic diagnosis.…”

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 …”

“…6 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). 2,4,[7][8][9][10][11][12][13][14][15][16][17][18][19][20] However, the known genetic defects can only explain~60% of the individuals affected by MMAF. 17 In this study, we reported an infertile male with MMAF from a consanguineous family.…”

“…D, The immunofluorescence staining detection indicated that Cfap65 was dominantly expressed in the cytoplasm of the spermatogonia (a), round spermatids (steps 1-8) (b), early elongating spermatids (steps 9-12; c-d) as well as late elongating spermatids (step 13-14; E) and in the flagella of epididymal spermatozoa (f). (green, CFAP65; blue, DAPI) [Colour figure can be viewed at wileyonlinelibrary.com] indicating that it may play an important role in the formation of sperm flagella in mouse, which would be proved by a Cfap65 knockout mouse model and further functional study.4 | DISCUSSIONSince 2014, when MMAF was defined, studies have shown that mutations in genes associated with sperm flagellum development may lead to MMAF 2,4,[7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Here, another candidate gene, CFAP65, was identified in an infertile male with MMAF by WES.…”