FA2019 page 47: I-cell disease (inclusion cell disease/mucolipidosis type II)—inherited lysosomal storage disorder; defect in N-acetylglucosaminyl-1-phosphotransferase → failure of the Golgi to phosphorylate mannose residues (forming mannose-6-phosphate) on glycoproteins → proteins are secreted extracellularly rather than delivered to lysosomes. Results in coarse facial features, gingival hyperplasia, clouded corneas, restricted joint movements, claw hand deformities, kyphoscoliosis, and high plasma levels of lysosomal enzymes. Often fatal in childhood.

I-cell trafficking disease: Failure Golgi to phosphorylate mannose residues so, decrease mannose 6 phosphate: coarse facial features, restricted joint movements, high plasma levels of lysosomal enzymes.

• I-cell disease is an autosomal recessive inherited lysosomal storage disease that results from a defect in N-acetylglucosaminyl-1-phosphotransferase enzymes.

*results in a defect of addition of mannose phosphate to lysosomal enzymes.

• This results in the failure of mannose residue phosphorylation of lysosomal hydrolases, which subsequently leads to their abnormal expulsion from the cell instead of to their normal site of action within the lysosome.

• Presents with coarse facial features, generalized hypotonia, bilateral hip dislocation, and inguinal hernias. Also presents with developmental delay and delayed growth.

• increase serum activity of lysosomal enzymes.