ADH5 and necrotizing enterocolitis: Of the cofactors, vitamins, prosthetic groups, and pigment subsystems represented within the Group A of higher abundance genes detected in the pre-NEC sample, two sets were associated with tetrapyrroles (specifically heme and siroheme biosynthesis; precorrin-2 oxidase [EC 1.3.1.76] and sirohydrochlorin ferrochelatase [EC 4.99.1.4]) while the third was associated with folate and pterines (YgfZ; S-(hydroxymethyl)glutathione dehydrogenase [EC 1.1.1.284]).