At least some of the increase in lean mass was attributable to an increase in body length (Figure 1E), a finding that was also observed in mice with germline MC4R mutations (4) and mice with PVN-specific Gq/11α deficiency (11) but not in obese mBrGsKO mice (18). Here, MC4R is linked to hyperinsulinemic hypoglycemia, familial, 4.