PGP and obesity due to melanocortin 4 receptor deficiency: DNA methylation is an active mechanism in the regulation of ABCB1 expression.30 Epigenetic mechanisms such as DNA methylation could also constitute a possible mechanism by which obesity—as assessed by BMI—could affect P-gp expression.30 It is well-known that obesity per se is often related to a variety of potentially stressful responses such as insulin resistance, altered nutritional status and chronic low-grade inflammation.31, 32 Moreover, obesity is known to be associated with an increased cancer risk,32, 33 which might also reflect deleterious epigenetic alterations.