AP3B1 gene mutation leads to incomplete formation of adaptor protein 3 (AP-3) complex, resulting in lysosomal-related cell dysfunctions (9, 10): (1) In melanosomes, impaired tyrosinase transport reduces melanin synthesis; (2) The decrease or absence of dense particles in platelets leads to platelet storage pool deficiency, resulting in impaired platelet function (11, 12); (3) In neutrophils, abnormal transport of azurophilic granule leads to impaired cell maturation, resulting in neutropenia (9, 13); (4) Natural killer (NK) cell function is impaired (5, 10). Here, AP3B1 is linked to Decreased total neutrophil count.