TMEM18 and obesity due to melanocortin 4 receptor deficiency: Among the available phenotypes, obesity was chosen because it has been subjected to a number of high quality and well-powered GWAS that have identified more than 100 loci, many that have been consistently replicated across studies (e.g. FTO, BDNF, MC4R, TMEM18, SEC16B) [18–20] .