Due to her lack of weight loss, history of pediatric obesity, and high suspicion of genetic contribution to weight gain, genetic testing was performed, and the variant c.574G > A p.(Val192Ile) and the variant c.661 A > G p.(Asn221Asp) were detected, both in heterozygosity, in the UCP3 and PCSK1 genes, respectively. This evidence concerns the gene UCP3 and obesity due to melanocortin 4 receptor deficiency.