Probable C-mannosyltransferase that mediates C-mannosylation of tryptophan residues on target proteins. Required during spermatogenesis for sperm head elongation and acrosome formation (PubMed:21397063, PubMed:21397064). Also plays a role in acrosome attachment to the nuclear envelope (By similarity). Interacts with FAM209. Colocalizes with DPY19L2 at the inner nuclear membrane. Widely expressed with high expression in testis. Not detectable in ejaculated sperm (at protein level). The disease is caused by variants affecting the gene represented in this entry. Deletions in DPY19L2 are probably the major cause of SPGF9. It has been suggested that DPY19L2P1 is an inactive pseudogene from which DPY19L2 has evolved by duplication. However, expressed transcript sequences derived from the DPY19L2P1 locus are known to exist. Belongs to the dpy-19 family. Truncated N-terminus. Truncated N-terminus.