Catalyzes the production of spermine from spermidine and decarboxylated S-adenosylmethionine (dcSAM). {ECO:0000269|PubMed:18367445, ECO:0000269|PubMed:18550699, ECO:0000269|PubMed:23696453, ECO:0000269|PubMed:23897707}. This is the function of ENSG00000102172 (SMS, spermine synthase).