HGD and freckles: The largest differences found in the gene expression profile of melasma patients included a nine-fold upregulation of guanine deaminase, a two-fold upregulation of homogentisate 1,2 dioxygenase, a 1.75-fold increase in tyrosinase-related protein 1, and a 1.27-fold increase in tyrosinase [13]. Contrastingly, genes involved in peroxisome proliferator-activated receptor (PPAR) signaling pathway such as adiponectin, C1Q, collagen domain-containing, adipocytes, and fatty acid-binding-protein 4 were down-regulated (>2 fold) in melasma patients [13].