FSTL1 and obesity due to melanocortin 4 receptor deficiency: To identify genetic and nongenetic variables, we performed backward stepwise regression, i.e., a sequential procedure of removing one input variable at a time in order to build up a regression model in which the dependent variable (i.e., FSTL1 protein level) is characterized as the linear combination of independent variables (i.e., SNP genotype, obesity status, sex, and age).