GO:0047012:   sterol-4-alpha-carboxylate 3-dehydrogenase (decarboxylating) activity
Catalysis of the reaction: NAD(P)+ + 3-beta-hydroxy-4-alpha-methyl-5-alpha-cholest-7-ene-4-beta-carboxylate = NAD(P)H + H+ + CO2 + 4-alpha-methyl-5-alpha-cholest-7-en-3-one.