ID4 and type 2 diabetes mellitus: This effect was associated with increased BMP/SMAD signalling in beta cells from donors with type 2 diabetes, as assessed by upregulated expression of the BMP target genes ID1, ID2, ID3 and ID4 (1.8-, 1.4-, 2.2- and 1.4-fold, respectively, p<0.05, Fig. 2e).