NEGR1 and obesity due to melanocortin 4 receptor deficiency: Neural growth regulator 1 (Negr1) – also known as kilon or neurotractin – is among the first common variants that have been associated with body mass index (BMI) (Thorleifsson et al. 2009; Willer et al. 2009; Speliotes et al. 2010), implicating Negr1 in the etiology of obesity.