GH1 and obesity due to melanocortin 4 receptor deficiency: The HG9 strain represents a major epistasis-based obese mouse model and promises to aid in the understanding of obesity and specifically the modulation of adipose tissue deposition by Gh. Studies are currently underway to identify the causative mutation and to characterize the effects of age and diet on obesity in this strain as well as testing for other physiological consequences such as alterations in food intake and insulin sensitivity.