Mucolipidosis Type IV Natural History Study

Inclusion Criteria: * Patient of any age or gender with a diagnosis of MLIV confirmed through 1) genetic testing and identification of homozygous MCOLN1 allele variants known to be pathogenic, or 2) clinical characteristics consistent with MLIV and one of the following: a) electron microscopy of fibroblasts or other patient cells demonstrating abnormal lysosomal accumulations consistent with MLIV, or b) elevated gastrin levels (pathognomonic for MLIV in the setting of a neurodevelopmental disorder). Potential participants or guardians must be able to provide informed consent (patient assent is not applicable to the MLIV population). Exclusion Criteria: * Patients will be excluded from data collection if they do not meet any of the diagnostic criteria outlined above or they and their guardians are unable to provide informed consent. It may be possible that an initial review of collected medical records by MGH research staff after consent and enrollment suggests a misdiagnosis of MLIV. In this case the subject will be excluded from the study. Research staff will contact the patient/guardians by email and schedule a telephone or teleconference meeting to discuss the decision. All medical records will be immediately destroyed upon exclusion of a participant.