GRB10 and obesity due to melanocortin 4 receptor deficiency: This is an interesting phenotype given the fact that Kv1.3-null mice, oppositely, are resistant to diet-induced obesity, are smaller and physiologically thinner than age-matched wild-type animals, and have increased mobility and metabolism [15,54,55] – while having an increased expression of Grb10 protein that reinforces its function as a growth inhibitor [47].