The function of PRND (prion like protein doppel, Ensembl gene identifier ENSG00000171864) is as follows. Required for normal acrosome reaction and for normal male fertility (By similarity). Can bind Cu(2+) (PubMed:15218028, PubMed:20411530). {ECO:0000250|UniProtKB:Q9QUG3, ECO:0000269|PubMed:15218028, ECO:0000269|PubMed:20411530}.