For example, in studies of vitamin D receptor (VDR) and CYP27B1-hydroxylase deficiency (which impairs 1,25(OH)2D formation) knockout mice, loss of vitamin D signaling results in increased levels of Bacteroides and Proteobacteria, with fewer normal Firmicutes including Ruminococcaceae, Lachnospiraceae, and Lactobacillaceae5. Here, CYP27B1 is linked to hyperinsulinemic hypoglycemia, familial, 4.