GPR18 and obesity due to melanocortin 4 receptor deficiency: Pharmacological modulation of GPR55 (unless otherwise stated) and GPR18 in the skeletal muscle could alter markers such as; nuclear factor of activated t-cells (NFAT), peroxisome proliferator-activated receptor-gamma coactivator alpha (PGC1α), pyruvate dehydrogenase kinase 4 (PDK4), adaptor protein, phosphotyrosine interaction, PH domain and leucine zipper containing 1 (APPL1), which are influenced by calcium signalling [22,23,24,25] and may be a beneficial treatment for obesity.