For example, tubby mice—which exhibit a loss-of-function mutation in the TUB gene, the founding member of the Tubby family—manifest an obese phenotype (Coleman and Eicher, 1990), and homozygous mutation in TUB has been associated with early-onset obesity in humans (Borman et al., 2014). Here, TUB is linked to obesity due to melanocortin 4 receptor deficiency.