Patients and their siblings undergo physical examination, a review of medical and family history, and blood pressure and anthropometric measurements. Patients and their siblings also undergo blood sample collection for laboratory studies (including analysis of C-reactive protein and CBC; lipid profile and triglycerides; leptin and adipokines; free thyroxine, TSH, IGF1, IGF3, and LH; and estradiol [females] or testosterone [males]); urine sample collection for microalbumin determination; and other study procedures (including euglycemic insulin clamp study; body composition and bone density [DEXA] study; bone-age x-ray [for patients < 18 years of age]; and vascular studies). Patients also undergo growth hormone stimulation testing.