Catalyzes the three-step monooxygenation required for the demethylation of 4,4-dimethyl and 4alpha-methylsterols, which can be subsequently metabolized to cholesterol (PubMed:21285510, PubMed:23583456, PubMed:26114596, PubMed:28673550, PubMed:36958722). Also involved in drug metabolism, as it can metabolize eldecalcitol (ED-71 or 1alpha,25-dihydroxy-2beta-(3-hydroxypropoxy)- cholecalciferol), a second-generation vitamin D analog, into 1alpha,2beta,25-trihydroxy vitamin D3; this reaction occurs via enzymatic hydroxylation and spontaneous O-dehydroxypropylation (PubMed:26038696). {ECO:0000269|PubMed:21285510, ECO:0000269|PubMed:26038696, ECO:0000269|PubMed:28673550, ECO:0000269|PubMed:36958722, ECO:0000305|PubMed:23583456, ECO:0000305|PubMed:26114596}. This is the function of ENSG00000052802 (MSMO1, methylsterol monooxygenase 1).