Williams syndrome's key features include supravalvular aortic stenosis, pulmonary valvular or peripheral pulmonary artery stenosis, atrial septal defect and / or ventricular septal defect, renal artery stenosis, aortic anomalies, elfin facies, and hypercalcemia of unknown pathophysiology; infants may also be small for gestational age, and hypercalcemia can be noted early in infancy, usually resolving by age 12 months.