Broadly, the disease can be sub-divided into mild and severe types, both very rare, although there is probably a continuum of phenotypes. In the most severe type there is hepatosplenomegaly, severe dysostosis multiplex, deafness, progressive mental retardation and often early death. In the milder form there is a later onset and more prolonged course with less severe dysostosis multiplex and mental retardation, but deafness is a major problem.
Deficiency of lysosomal a-mannosidase is the primary defect.
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