What is the most likely diagnosis for a 3-year-old girl with coarse facial features and contractures found to have increased lysosomal enzyme activities?

The presentation of coarse facial features and joint contractures in a young child, combined with the finding of increased lysosomal enzyme activities, strongly suggests I-cell disease, also known as mucolipidosis type II.

I-cell disease is characterized by a defect in the enzyme responsible for adding mannose-6-phosphate to lysosomal enzymes, which prevents these enzymes from being correctly targeted to the lysosomes. As a result, there is an accumulation of lysosomal enzymes in the blood, leading to their increased activities in the serum, while the lysosomes themselves are deficient in these enzymes. The coarse facial features and skeletal abnormalities, such as contractures, are distinctive clinical features of the disease.

In contrast, although mucopolysaccharidosis, lysosomal storage diseases, and Gaucher disease all present with various forms of storage issues within lysosomes and may share some overlapping symptoms, they do not typically present with the same combination of symptoms or the specific laboratory findings noted in this case. Mucopolysaccharidoses generally involve issues with glycosaminoglycan metabolism, while Gaucher disease is characterized by glucocerebrosidase deficiency leading to splenomegaly and bone pain rather than the distinct facial and contracture deformities seen