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Patients had short stature, hypopigmented skin, coarse facial features, and recurrent bronchopulmonary infections due to Streptococcus pneumoniae. Affected individuals had consistently low peripheral neutrophil counts, with absolute neutrophil counts less than 500 per microliter, although neutrophil maturation in the bone marrow was intact. Compared to healthy sibs, CD8(+) cytotoxic T cells from affected individuals had decreased cytotoxic activity. Structural and functional analysis of patients' immune cells and melanocytes suggested abnormal maturation and function of specialized lysosomes in cytotoxic T cells, melanocytes, and neutrophil granulocytes.