Protein-lysine N-methyltransferase. Monomethylates PRMT5, modulating its transcriptional activity (PubMed:38438251). May also act as a histone methyltransferase (By similarity). Plays a critical role in cardiac development. Acts as a key epigenetic regulator of gene expression during cardiac development via its dual activities as a methyltransferase and negative regulator of HDAC1 (By similarity). . This is the function of Ensembl gene identifier ENSG00000186532 (SMYD4, SET and MYND domain containing 4).