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Parents bring in their 1.5 year old infant for the fifth time this year because of recurring fevers. "It seems like every month for 2 or 3 days, our child doesn't feel well," they say. "I think I had it," the dad says, "and my dad too, and my sister, and my aunt. My sister actually died of a clostridium infection when she was a child." You look into the patient's past medical record, and 3 weeks ago, the child presented with pharyngitis, and 3 weeks before that, with a bacterial skin infection, and 3 weeks before that, malaise, and 3 weeks before that, gingivitis.

On exam, you notice significant gingival disease and chronic mouth ulcers. The child looks otherwise normal, with a normal growth curve, no dysmorphic features, and no hepatosplenomegaly. Labs are surprising. At each visit, the child's ANC (absolute neutrophil count) is around 200-400. But labs drawn at "well-child visits" when he is not sick show a normal CBC.

Challenge: What's your diagnosis?