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The purpose of this study is to define the natural history of Mucolipidosis Type IV and identify potential clinical outcome measures.

Mucolipidosis type IV (MLIV) is an autosomal recessive disorder typically characterized by severe psychomotor delay evident by the end of the first year of life and slowly progressive visual impairment during the first decade as a result of a combination of corneal clouding and retinal degeneration. By the end of the first decade of life, and always by their early teens, individuals with typical MLIV develop severe visual impairment as a result of retinal degeneration. MLIV is an under-diagnosed and unique lysosomal disorder in that it often is mistaken either for cerebral palsy or for a retinal dystrophy of unknown cause. In addition, it is caused by a defect in a cation channel rather than by a lysosomal hydrolase. This study represents the only prospective clinical study in this patient population. Now that an animal model has been created and novel therapies will likely be tested, it is particularly important to define the natural history of this disorder and identify potential clinical outcome measures.

Inclusion Criteria:

Subjects must:

• Have a definitive diagnosis of MLIV based at least on a compatible history and significantly elevated blood gastrin levels
• Be able to travel to the Baylor Institute of Metabolic Disease in Dallas and spend 2-3 working days on site
• Be able to tolerate a general exam and neurological exam
• Be able to tolerate a modest amount of blood drawing, provide a urine specimen, and have a skin biopsy(if not previously done)
• Be able to tolerate the performance of necessary neuroimaging studies to include EEG and Head MRI
• Be able to tolerate a neuropsychological testing and rehabilitation evaluation

Exclusion Criteria:

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Subjects previously identified with Mucolipidosis Type IV