NR1I2 and type 2 diabetes mellitus: Indolepropionic acid (IPA) is a deamination product of tryptophan that can only be produced by gut microbes.24 It regulates gastrointestinal barrier function via its interaction with the pregnane X receptor (PXR), which is predictive of the onset of type 2 diabetes,16 has been shown to be strongly correlated with higher gut microbiome diversity and its levels in serum are determined primarily by gut microbiome composition.25