Coiled-coil domain-containing protein 34
sperm midpiece
Homozygous mutations in <i>CCDC34</i> cause male infertility with oligoasthenoteratozoospermia in humans and mice.
<h4>Background</h4>Oligoasthenoteratozoospermia is a typical feature of sperm malformations leading to male infertility. Only a few genes have been clearly identified as pathogenic genes of oligoasthenoteratozoospermia.<h4>Methods and results</h4>Here, we identified a homozygous frameshift variant (c.731dup, p.Asn244Lysfs*3) in <i>CCDC34</i>, which is preferentially expressed in the human testis, using whole-exome sequencing in a cohort of 100 Chinese men with multiple morphological abnormalities of the sperm flagella (MMAF). In an additional cohort of 167 MMAF-affected men from North Africa, Iran and France, we identified a second subject harbouring a homozygous <i>CCDC34</i> frameshift variant (c.799_817del, p.Glu267Lysfs*72). Both affected men presented a typical MMAF phenotype with an abnormally low sperm concentration (ie, oligoasthenoteratozoospermia). Transmission electron microscopy analysis of the sperm flagella affected by <i>CCDC34</i> deficiency further revealed dramatic disorganisation of the axoneme. Immunofluorescence assays of the spermatozoa showed that <i>CCDC34</i> deficiency resulted in almost absent staining of CCDC34 and intraflagellar transport-B complex-associated proteins (such as IFT20 and IFT52). Furthermore, we generated a mouse <i>Ccdc34</i> frameshift mutant using CRISPR-Cas9 technology. <i>Ccdc34</i>-mutated (<i>Ccdc34<sup>mut/mut</sup></i> ) male mice were sterile and presented oligoasthenoteratozoospermia with typical MMAF anomalies. Intracytoplasmic sperm injection has good pregnancy outcomes in both humans and mice.<h4>Conclusions</h4>Our findings support that <i>CCDC34</i> is crucial to the formation of sperm flagella and that biallelic deleterious mutations in <i>CCDC34</i>/<i>Ccdc34</i> cause male infertility with oligoasthenoteratozoospermia in humans and mice.