In IGF-1 deficiency, anorexia nervosa (4), aging (5), and hypopituitarism (3), serum IGF-1 concentrations are reduced, leading to decreased bone weight or the slowing of growth due to a lack of physiologic effects of IGF-1 on osteoblasts. This evidence concerns the gene IGF1 and hyperinsulinemic hypoglycemia, familial, 4.