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Mucolipidosis II (or I-cell disease) (MLII) is a rare autosomal recessive lysosomal storage disease due to N-acetylglucosaminyl 1-phosphotransferase deficiency. This leads to the defective lysosomal targeting of many lysosomal enzymes. Clinical and radiological signs are similar to those in Hürler`s disease, although onset is earlier (during the first months of life, or sometimes even before birth). The disorder is fatal during childhood because of cardiorespiratory complications. It is characterized by hypertrophic gingivae and enlarged tongue, coarse facies, hirsutism, hernias, cutaneous infiltration, limited joint mobility, dysostosis multiplex, hepatosplenomegaly, corneal opacities, deafness, mental and motor retardation (obvious as early as the age of 6 months), and dwarfism. Biologically, acid hydrolase activities show a striking increase in the serum, while they are decreased in cultured fibroblasts. The primary deficiency of phosphotransferase has been demonstrated occasionally. This multimeric enzyme is composed of 3 polypeptide subunits encoded by 2 different genes (for alpha/beta and gamma). Gene coding for the a/b subunits (localized on chromosome 12p) is altered in MLII. Prenatal diagnosis is available (on the trophoblast or amniotic fluid). Treatment is symptomatic (biphosphonates have been proposed for bone disease). Several cases of bone marrow transplantation have been reported with some benefits
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