In the ob/ob mouse, for example, knockout of leptin affects its action on adipose tissue, the brain and the adrenal glands causing morbid obesity, dyslipidaemia, and elevated glucocorticoid signalling (Livingstone et al., 2009) that are likely to compound the direct action of leptin on muscle by potentially affecting muscle through indirect signalling pathways. Here, LEP is linked to morbid obesity.