RLN3 and obesity due to melanocortin 4 receptor deficiency: Furthermore, relaxin-3 KO mice (C57BL/6J background) do not display any overt differences in feeding or bodyweight under normal housing and dietary conditions (Watanabe et al., 2011b; Smith et al., 2012), despite an earlier report that mixed (129S5:B6) background relaxin-3 KO mice fed on a diet with higher than normal (moderate) fat content were largely resistant to the obesity observed in WT controls (Sutton et al., 2009).