SLN and obesity due to melanocortin 4 receptor deficiency: In addition, in view of the previous study indicating that sarcolipin levels are undetectable in mouse skeletal muscle [7], which suggests that there is little value in knocking out sarcolipin, we have examined the effects of over-expressing sarcolipin and an epitope-tagged (FLAG) variant of sarcolipin in mouse skeletal muscle on high fat diet-induced obesity and energy expenditure.