Xenobiotic chemicals exhibiting EA often interact with more than one estrogen receptor (ER) subtypes [3–6] and can produce many biological and adverse health effects in mammals, such as early puberty in females, reduced sperm counts, altered functions of reproductive organs, obesity, altered sex-specific behaviors, and increased rates of some breast, ovarian, testicular, and prostate cancers [1–9]. Here, ESR1 is linked to obesity due to melanocortin 4 receptor deficiency.