Lysosome-related organelles have versatile functions including protein and lipid degradation, signal transduction, and protein secretion. The molecular elucidation of rare congenital diseases affecting endosomal/lysosomal biogenesis has given insights into physiological functions of the innate and adaptive immune system.. Here, we describe a novel human primary immunodeficiency disorder and provide evidence that the endosomal adaptor protein p14, previously characterized as confining mitogen-activated-protein-kinase (MAPK) signaling to late endosomes, is critical for the function of neutrophils, B-cells, cytotoxic T-cells and melanocytes. Combining genetic linkage studies and transcriptional profiling analysis, we identified a homozygous point mutation in the 3’ UTR of p14 (also known as MAPBPIP), resulting in decreased protein expression. In p14-deficient cells, the distribution of late endosomes was severely perturbed, suggesting a novel role for p14 in endosomal biogenesis. These findings have implications for understanding endosomal membrane dynamics, compartmentalization of cell signal cascades, and their role in immunity. Keywords: Interindividual comparison.

EBV-transformed B cell lines from 2 parents and 2 affected children