1. This case report describes a Japanese boy with a mild form of Mucolipidosis IV (MLIV), which is typically associated with intellectual disability, corneal opacities, and motor delays. 2. Serial MRI findings in the boy showed thinning of the corpus callosum, white matter volume reduction, and signal abnormalities. Exome sequencing revealed compound heterozygous mutations in the MCOLN1 gene associated with MLIV. 3. Unique features in this case included a relatively mild course, novel mutations, and elevated serum gastrin levels. Serial MRI also showed signs of cerebellar atrophy and iron accumulation over time. Whole exome sequencing was important for correctly diagnosing this rare