Loss-of-function mutations in the ADCY3 gene, encoding for AC3, or loss of ADCY3 expression cause monogenic severe obesity and increase the risk for type 2 diabetes (Cao et al., 2016; Grarup et al., 2018; Nordman et al., 2005; Saeed et al., 2018; Siljee et al., 2018; Wang et al., 2009). This evidence concerns the gene ADCY3 and type 2 diabetes mellitus.