NRG4 and obesity due to melanocortin 4 receptor deficiency: Human studies have suggested that patients with obesity who are metabolically healthy (prevalence of 10-30% amongst patients with obesity) have better adipose tissue function, less ectopic fat storage, and more insulin sensitivity than MU patients [18]. Those patients who are MU have an increased level of circulating inflammatory markers, including higher levels of C-reactive protein, progranulin, and chemerin, and lower levels of adiponectin and neuregulin-4 [19].