LEPR and obesity due to melanocortin 4 receptor deficiency: However, certain obesity-associated genes, such as proliferator-activated receptor-γ (PPARG), lipoprotein lipase (LPL), leptin receptor (LEPR), paraoxonase (PON1 and PON2) and tumor necrosis factor-α (TNF-α), are also being further investigated for possible associations as risk factors for breast cancer development.51–53 Single nucleotide polymorphisms (SNPs) within these genes can increase breast cancer risk by altering the expression of DNA repair genes, changes in hormone receptor expression and pathways involved in tumor growth and progression.