A concerned mother brings her 6 year-old son to your office. She tells you that over the past 3 months the boy has been having severe fatigue, easy bruising, recurrent infections, fever, night sweats, and unintentional weight loss. He has had four spontaneous nose bleeds in the last two weeks alone. He was born in an Amish family when his mother was 45-years old in Belleville, a rural town in Pennsylvania, USA. His family history is significant for genetic disorders. You notice that the boy has a pale flat face, wide-set eyes with white spots on the periphery of iris, epicanthal folds, a single palmar crease across each hand. Pharynx is normal with no tonsillar exudate. On cardiac auscultation, you hear a holosystolic murmur that is consistent with a ventricular septal defect. Other physical examination findings include hepatomegaly, splenomegaly, lymphadenopathy, and a petechial rash over his entire body. Of the following, which is the most likely diagnosis in this patient?
