ACE and obesity due to melanocortin 4 receptor deficiency: The final step (F2), etiological investigation, incorporating advanced imaging techniques as well as genetic testing, biopsies, and specialized laboratory tests, such as serum electrophoresis, serum free light chains, serum angiotensin-converting enzyme, plasma metanephrines, has to be applied to identify the underlying cause [45] in patients who are obese when a specific etiology of heart failure is suspected, despite the difficulties described and the possibility that obesity itself may be the underlying etiology.