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Mucolipidosis III (MLIII) or pseudo-Hurler-polydystrophy is similar to the more moderate forms of Hurler`s disease such as Scheie`s or Hurler-Scheie`s syndromes. Just as in MLII, MLIII, its milder form, is due to UDP-N-acetylglucosamine : lysosomal enzyme N-acetylglucosaminyl 1-phosphotransferase deficiency, leading to the defective lysosomal targeting of many lysosomal enzymes. The condition is autosomal recessive and very rare. The first clinical abnormality concerns joint stiffness leading to the diagnosis during childhood. Dysostosis multiplex is similar to Hurler`s disease, but facial dysmorphy is less severe and affected individuals reach a stature of over 150 cm. Intelligence may be normal but most children have difficulties to follow their age group at school : this finding could be related to hearing difficulties. Corneal clouding appears as the disorder progresses. This condition is compatible with a prolonged lifespan. Biologically, many 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. The disease is genetically heterogeneous : classical MLIII present with a/b gene alterations while variant MLIII present with g gene (localized on chromosome 16p) alterations. Prenatal diagnosis is available (on the trophoblast or amniotic fluid). Treatment is symptomatic, mainly orthopedic. A hearing aid and speech therapy may also be necessary. |