C3 and obesity due to melanocortin 4 receptor deficiency: Classical and alternate complement pathways have been implicated, with elevation in C3, C4, properdin, factor B and factor D [7,10] having been reported in PCOS (Figure 1), though their expression was correlated to obesity and insulin resistance [7]; however, there are conflicting reports on complement proteins, suggesting that C3 may be elevated and related to inflammation [8,9,10] whilst others report that C3 levels are unchanged [11].