Introduction by Roger L. Berkow, MD, FAAP Persistent Bleeding in a 7-week-old Girl Acute Right Arm Swelling in a 6-month-old Girl Thrombocytopenia in a 7-day-old Male Refusal to Bear Weight in a Previously Healthy 8-year-old Girl Neutropenia, Recurrent Infections, and Warts in a 6-year-old Boy Acute-Onset Digital Ischemia in a Previously Healthy 7-year-old Boy Treatment-Resistant Bacterial Lymphadenitis in an Otherwise Healthy Girl Persistent Hypoxemia in an Asymptomatic 4-year-old Boy Multifocal Bone Pain, Fevers, and an Enhancing Clavicular Lesion in an 11-year-old Liberian Boy Forehead Swelling and Fever in a 12-year-old Ugandan Boy Acute Weakness in a Toddler with Sickle Cell Disease New-Onset Jaundice in an 11-month-old Boy Headache, Vomiting, and Syncope in a 17-year-old Girl Microcytic Anemia Iron-Refractory Iron Deficiency Anemia in an 11-year-old Girl An 18-month-old Girl with a Fleshy Mass in the Ear Canal Isolated Swelling of the Uvula in a 2-year-old Girl Leg Pain, Refusal to Walk, and Tibial Bone Erosion on Radiographs in a 7-year-old Boy Undifferentiated Shock in a 2-month-old Girl Migratory Arthralgia in a 3-year-old Girl.