In the Mcoln1−/− mouse, myelination defects are found primarily in the CRB [9, 28]; however, our data suggest a regional variability in hypomyelination in different human brain regions, and reduced levels of myelin proteins may reflect degeneration in the cerebellum in this patient as has been reported for other older MLIV patients [26]. Here, MCOLN1 is linked to mucolipidosis type IV.