Intraflagellar transport (IFT)-associated protein required for spermatogenesis (PubMed:30929735). Required for sperm flagellar formation and intraflagellar transport (PubMed:30929735). Interacts with IFT20 (PubMed:30929735). Interacts with IFT52 (PubMed:30929735). Interacts with IFT140 (PubMed:30929735). Strongly expressed in testis. Expressed in preleptotene spermatocytes, pachytene spermatocytes, round spermatids and elongated spermatids (at protein level). The disease is caused by variants affecting the gene represented in this entry. Belongs to the TTC21 family. Truncated N-terminus.