Clinical features of the index patient. (A) Absolute neutrophil count (ANC) course since diagnosis. Clinically suspected pneumonia occurred at 6 years of age. Initially, the patient exhibited a clinical response with an increase in ANC with 5 µg/kg of G-CSF. However, there was no response in ANC rise within 14 days of a subsequent G-CSF treatment, even with dose escalation to 10 µg/kg. (B) The bone marrow (BM) aspirate smears exhibited granulocytic hypoplasia and promyelocytes/myelocytes with large size and multinucleation, and bizarre complex hypersegmentation in very large maturing granulocytes (red arrows) (Wright-Giesma stain, ×500). Results of the core biopsy showed cellular marrow with erythroid predominance, granulocytic hypoplasia, and small clusters of abnormal cells suspicious of left-shifted granulocytes with abnormal morphology seen in the aspirate smears (hematoxylin and eosin [H&E] stain, ×200). There is also increased apoptosis (green arrows). Immunohistochemistry (IHC) staining show granulocytic hypoplasia with a small number of cells stained with myeloperoxidase (black arrow). (C) The pedigree shows that only 1 of 3 children showed neutropenia and carried the LCP1 I232F mutation. The parents were asymptomatic and did not have the mutation in LCP1. The other 2 children were not affected and not tested for the mutation. (D) Schematic representation of LCP1 protein shows the domain organization and the location of the mutation within ABD1 in the CH1.