 The mechanism of mutation in FIG4 causing Yunis–Varon syndrome involves altering conversion of phosphatidylinositol 3-phosphate (PI3P) to signaling lipid phosphatidylinositol 3,5-bisphosphate(PI(3,5)P2).Because this conversion in endosomal membranes changes dynamically with fission and fusion events to create/absorb intracellular transport vesicles, enlarged cytoplasmic vacuoles have been found in patient neurons, muscle, and cartilage.These have been identified as intracytoplasmic vacuoles(fluid sacs inside cellular cytoplasm) causing excessive build-up of vacuolated macrophages in bone marrow and pericardial fluid in the heart.