Society for Mucopolysaccharide Diseases
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This glycoproteinosis, which affects primarily the reticuloendothelial (RE) system, is caused by deficiency of lysosomal neuraminidase (NEU1) and consequent accumulation of sialylated glycoconjugates.
MLI is a rare disorder; the exact prevalence is unknown but is probably around 1:2,000,000 births.
The disorder is usually divided into three phenotypes:
1. A congenial form: These infants are delivered either stillborn or they die within the first two years of life.
2. An infantile form: Death usually occurs by the second decade of life, but reports exist of patients surviving into the early third decade of life. These patients have mild facial dysmorphism, enlargement of the liver and spleen, mild bony dysostosis and progressive learning difficulties.
3. An adult form: These patients usually do not die from the disease, but they experience decreased visual acuity with “cherry red spots” and myoclonic seizures (“drop attacks”). This disorder is often called the “cherry red spot-myoclonus syndrome.
Diagnosis
Definitive diagnosis is made by demonstrating a deficiency of neuraminidase activity, which can be measured in white blood cells or cultured fibroblasts. Detection of an abnormal pattern of urinary oligosaccharides can be used as an initial screening test.
Treatment
There is no curative treatment for MLI. Enzyme replacement therapy has been performed with some success in a mouse model of the disease.
