HTR2A and obesity due to melanocortin 4 receptor deficiency: In humans, genetic studies have reported that polymorphisms in Htr genes (for example, HTR1A, HTR1Dβ, and HTR2A) are associated with obesity (Gorwood et al., 2002; Levitan et al., 2006; Compan et al., 2012; Oh et al., 2015).