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Sialidosis type 1

Synonym(s) Cherry-red spot-myoclonus syndrome
Normomorphic sialidosis
Prevalence <1 / 1 000 000
Inheritance Autosomal recessive
Age of onset Childhood
  • E77.1
  • C0023806
MeSH -
MedDRA -


Sialidosis is a lysosomal storage disease belonging to the group of oligosaccharidoses or glycoproteinoses. Two types of sialidosis have been defined, type 1 and 2. Type 1 sialidosis is also called normomorphic or 'cherry-red-spot, myoclonus' syndrome. The incidence of all types of sialidosis is estimated at 1/4 200 000 live births. The disease begins at between 8 and 25 years of age, with walking difficulties and/or a loss of visual acuity. Almost all patients display a cherry-red spot on the retina. They may also have generalised myoclonus, in some cases associated with seizures. Colour vision progressively diminishes in association with the appearance of night blindness, corneal opacities and, in some cases, nystagmus. In contrast to type 2 sialidosis, patients do not show facial dysmorphism, bone dysplasia or psychomotor retardation. Sialidosis is caused by alpha D neuraminidase (or sialidase 1) deficiency leading to sialyloligosaccharide accumulation in body tissues. Transmission is autosomal recessive. The causative gene, NEU1 (located on 6p21), has been cloned and mutations have been identified. Detection of urinary sialyloligosaccharide excretion can evoke the diagnosis, but as excretion levels may be quite low, the diagnosis needs to be confirmed by demonstration of neuraminidase enzyme deficiency in leukocytes or, preferably, cultured fibroblasts. The main differential diagnosis is galactosialidosis (see this term), which characterised by deficiencies in both neuraminidase and beta galactosidase. For families at risk, the identification of related heterozygous individuals is very reliable if the two mutations are known in the index case. Prenatal diagnosis can be performed by measurement of enzyme activity or by molecular analysis if the mutations are known. In absence of any specific treatment, management should be multidisciplinary to allow for adapted symptomatic treatment, which is essential for improving the quality of life of affected patients. The myoclonic seizures often respond poorly to treatment. There appears to be no major effect on life expectancy.

Expert reviewer(s)

  • Dr Roseline FROISSART
  • Dr Irène MAIRE

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