Mucolipidoses

The mucolipidoses (MLs) are a group of diseases that may be confused phenotypically with the mucopolysaccharidoses (see Table...,30-4 ). In these rare diseases both lipids and mucopolysaccharides accumulate in tissues. '33I Each of the five types of mucolipodoses is an autosomal recessive disease. There is no specific race or ethnic predilection except for the ML IV type.

The first patients described with sialidosis (type 1) had myoclonic seizures and a retinal-macular cherry-red spot. y Age of onset varies, but older patients who were normal in early life predominate. Most patients remain clinically normal until adolescence. They then show initial neurological manifestations of myoclonus and visual and gait impairments. Once visual pathology is evident, including night blindness or loss of color vision, the disease becomes progressive. y A cherry-red spot is uniformly present. Lens opacities may occur. Myoclonus is typically generalized, and in some cases it may be stimulus-linked. Intellectual deterioration may be a late occurrence. Painful neuropathy, delayed nerve conduction velocity, generalized convulsive seizures, ataxia, and dysostosis multiplex ensue. Facies may be coarse but to a lesser extent than those seen in the mucopolysaccharidoses.

Lipomucosaccharidosis (type 2) has a very different clinical picture. The onset of symptoms always occurs early in life. Babies may be born with hydrops fetalis. The somatic and facial features are invariably coarse. Dysostosis multiplex, periosteal cloaking, and hepatosplenomegaly dominate, and contractures of major bony articulations, inguinal hernias, and mild hepatosplenomegaly are common findings. Angiokeratoma corporis diffusum may be more prominent in these patients than in those with sialidosis. Neurological impairment is slowly progressive and is marked by dementia and other signs such as ataxia, hypotonia, reduced muscle mass, and cherry-red spots. Foam cells and vacuolization of lymphocytes are seen in aspirated bone marrow.

Patients with I-cell disease (type 3) have coarse facial and somatic features and severe mental retardation. Mild forms of dysostosis multiplex are seen, but these are much less severe than those seen in patients with Hurler's disease.

Umbilical hernias, hepatosplenomegaly, kyphoscoliosis, and lumbar gibbus are all typical features of I-cell disease. These features are seen earlier than they are in patients with Hurler's disease, but they are not as severe. The thorax is usually small, joint movement is restricted, and the tongue is large, often with gingival hyperplasia. Corneal haziness is common, and cardiac involvement includes cardiomegaly and aortic insufficiency. These children are severely ill and frequently die in the first decade of life from cardiopulmonary failure.

Patients with pseudo-Hurler's disease have a later clinical onset, usually in childhood, and some may live into adulthood but are mentally retarded. Linear growth is severely affected, corneal clouding and aortic regurgitation are common, and older patients show joint stiffness. Facial coarseness is minimal. In the ML IV form, severe corneal clouding and psychomotor retardation are seen. Facial dysmorphism is not characteristic.

The mucolipidoses are most easily confused with the mucopolysaccharidoses. They are biochemically distinguishable by the lack of the mucopolysacchariduria characteristic of the MPS. There are some clinical and biochemical similarities with the GM 1 gangliosidoses. Detailed and skilled clinical evaluation of systemic as well as neurological factors is essential in addition to assays for lysosomal enzymes and mucopolysaccharides in the urine.

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