Baseline information collected includes: height, weight, head circumference, examinations by an endocrinologist and ophthalmologist, endocrine laboratory testing, fundus photography, electrophysiology testing, head MRI, and a developmental assessment. A glucagon stimulation test will be performed and subjects who are deemed GH-deficient and who have delayed growth will be assigned to GH treatment, in line with standard clinical practice. Those with normal growth but determined to be GH-deficient by a glucagon stimulation test will be randomized to treatment with GH vs control (no intervention; observation only).