MSTN and obesity due to melanocortin 4 receptor deficiency: Previous studies that investigated the association between serum myostatin levels and insulin sensitivity or resistance indices in adults with obesity and without type 2 diabetes were discrepant (Amor et al., 2019; Brandt et al., 2012; Carvalho et al., 2018; Hittel et al., 2010; Kern‐Matschilles et al., 2022; Toloza et al., 2018).