LEP and obesity due to melanocortin 4 receptor deficiency: In this line, single-gene mutations including those of LEP and LEPR genes are responsible for causing early-onset obesity [78], whereas genetic, genomic, and epigenetic alterations have been reported in syndromic forms of obesity, despite obesity typically being a multifactorial disorder showing a high heritability profile (50–75%), which is probably higher in early-onset cases [115].