A number of host factors including SNPs of interferons IL28A, IL28B, IL29, interferon-γ, MBL, IL -10, IL-18, CTLA4, TRAIL, TGF-β, MX1, Osteopontin, LMP7, OAS1 genes, insulin resistance, obesity and ethnicity, have been found to modulate the treatment response. The gene discussed is IFNL1; the disease is obesity due to melanocortin 4 receptor deficiency.