Dnajb13, a type II HSP40 family member, is highly expressed in the testis. It is an axonemal component of mouse mature spermatozoa, localized to the radial spokes of the '9+2' axoneme [3]. DNAJB13 is involved in sperm flagellar function, and may participate in spermiogenesis, sperm flagellum development, and the motility of mature spermatozoa [4,5].

In a study of 92 idiopathic asthenozoospermia patients and 200 men with normal fertility, a novel c.106T>C mutation of DNAJB13 was present in nearly 10% of the asthenozoospermia patients but absent in fertile men. Sperm from patients with this mutation had tail defects and reduced DNAJB13 protein levels, leading to immotility [1]. Another study identified a novel homozygous frameshift mutation of c.335_336del [p.E112Vfs*3] in DNAJB13 in a primary infertile male patient with teratozoospermia, which caused ultrastructural defects in his sperm [2]. Also, mutations in DNAJB13 have been found to cause primary ciliary dyskinesia (PCD) in humans, with affected individuals having recurrent respiratory-tract infections and most males being infertile due to sperm flagellar dysfunction [6].

In conclusion, Dnajb13 is crucial for sperm flagellar function, spermiogenesis, and sperm motility. Studies on DNAJB13 mutations in human patients have revealed its significance in male infertility and PCD. Understanding Dnajb13's function through these human-based genetic studies helps in comprehending the genetic mechanisms underlying male reproductive disorders and PCD.