Mucolipidosis IV (ML IV) is an autosomal recessive neurodegenerative lysosomal storage disorder characterized by psychomotor retardation and ophthalmologic abnormalities. ML IV is caused by mutations in mucolipin 1 (MCOLN1), a late endosomal/lysosomal ion channel. Cells from patients with MLIV accumulate enlarged vacuolar structures containing phospholipids, sphingolipids, mucopolysaccharides, and gangliosides. Accumulation of lipids results from defects in membrane transport along the late endocytic pathway. It was found that MCOLN1 is required for efficient fusion of both late endosomes and autophagosomes with lysosomes.
