INS and obesity due to melanocortin 4 receptor deficiency: Research involving American Indian adolescents and Korean children with obesity has demonstrated an inverse relationship between plasma 2-AAA levels and insulin sensitivity, with elevated 2-AAA concentrations observed in cellular and mouse models of obesity-related insulin resistance (Short et al., 2019; Lee et al., 2019; Plubell et al., 2018; Aggarwal et al., 2021).