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Sialidosis type 2

ORPHA87876
Synonym(s) Infantile dysmorphic sialidosis
Prevalence <1 / 1 000 000
Inheritance Autosomal recessive
Age of onset Neonatal
Infancy
ICD-10
  • E77.1
OMIM
UMLS -
MeSH -
MedDRA -

Summary

Sialidosis is a lysosomal storage disease belonging to the group of oligosaccharidoses or glycoproteinoses. Two types of sialidosis have been defined, type 2 (also referred to as the infantile, dysmorphic form of sialidosis) and type 1 (a later onset form without major dysmorphic features). The incidence of all types of sialidosis is estimated at 1/4 200 000 live births. Two forms of type 2 sialidosis have been described: a congenital or neonatal onset form, and an infantile form. The congenital form may manifest in utero with foetal hydrops or foetal ascites. The neonatal form is characterised by oedema, hepatosplenomegaly and ascites, as well as other clinical manifestations similar to those observed in Hürler disease (Mucopolysaccharidosis type 1, see this term) with a continuum of severity: facial dysmorphology, dysostosis multiplex, a short trunk with a prominent sternum, kyphosis, and umbilical and inguinal hernias. Surviving children display short stature (with a slowing of growth towards 18 months of age), hearing problems, a cherry-red spot on the retina (a constant feature after 3 years of age), corneal opacities, myoclonic seizures and developmental delay (delayed speech and walking), followed by psychomotor regression. Renal disease (nephrosialidosis) is present is some patients. More progressive, juvenile-onset forms with less pronounced dysmorphology, angiokeratomas and a cherry-red spot on the fundus have been described but appear to be forms of galactosialidosis. Cerebellar anomalies manifest at adolescence and are accompanied by a pyramidal syndrome or peripheral neuropathy. Sialidosis type 2 is caused by a mutation in the NEU1 gene (6p21) resulting in a deficiency of N-acetyl-alpha-neuraminidase (sialidase 1) and leading to the accumulation of sialyloligosaccharides. The disease is transmitted in an autosomal recessive manner. The diagnosis is suspected by detection of urinary sialyloligosaccharide excretion and can be confirmed by demonstration of the neuraminidase enzyme deficiency (in the presence of normal beta-galactosidase activity) in leukocytes or, preferably, cultured fibroblasts. The main differential diagnoses include galactosialidosis (characterised by deficiencies in both beta galactosidase and neuraminidase) mucopolysaccharidosis type I and mucopolysaccharidosis type 2 (see these terms). For families at risk, identification of heterozygotes is very reliable if the two mutations are known. Correct diagnosis of the form of the disease manifesting in utero is essential for allowing prevention of future pregnancies resulting in in utero death or terminations during the later stages of pregnancy. As no effective treatment is currently available, prenatal diagnosis (by measurement of enzyme activity or by molecular analysis if the mutation is known) should be offered to parents who already have an affected child. 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. In rare cases, allogeneic bone marrow grafts have been performed but did not prevent progression to renal insufficiency or worsening of the bone manifestations. The congenital form leads to still-birth or death within the first two years of life. For the other forms, life expectancy does not generally exceed two decades.

Expert reviewer(s)

  • Dr Roseline FROISSART
  • Dr Irène MAIRE

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Detailed information

Emergency guidelines
  • FR (2013,pdf)
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