OXT and obesity due to melanocortin 4 receptor deficiency: One factor that seems contrary to the adult-onset obesity phenotype observed at 8, 10 or 16 weeks in OT null mice is that finding that OT null mice tend to have a reduction in muscle regeneration by 12 weeks of age and a significant defect in muscle regeneration and a reduction of both muscle mass and fiber size by 52 weeks of age (Elabd et al., 2014) (characteristic of sarcopenia).