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A genetic neurodegenerative disease, divided into two types. These conditions are caused by a missing enzyme (sialidase) that results in the accumulation of sialic acid in the nerve cells. Type II is reported in infants and toddlers.

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Sialidosis type I: Cherry-Red-Spot, Myoclonus Syndrome

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Sialidosis type II: Mucolipidosis type I; Sialidase Deficiency; Glycoprotein Neuraminidase Deficiency; NEUG Deficiency; Lipomucopolysaccharidosis.

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Genetic disorder with a 2.5:1 male preponderance.

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Autosomal recessive. The majority of type I patients have been Italian. The lysosomal sialidase gene has been mapped to chromosome 6 (6p21.3). Prenatal diagnosis (amniotic fluid cells) is possible.

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The enzyme lysosomal neuraminidase (sialidase) normally removes the terminal sialyl linkages of several oligosaccharides and glycoproteins. Its deficiency results in excessive accumulation of complex sugars rich in sialic acid.

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Excessive urinary oligosaccharides can be demonstrated. Definitive diagnosis is based on sialidase activity present in tissue samples (e.g., fibroblasts, WBCs).

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Clinically, sialidosis can have two forms. Type I (mild form) presents with a cherry-red spot myoclonus phenotype that is usually associated with isolated neuraminidase deficiency. Nystagmus, ataxia, and seizures are reported. Type II (severe form) has abnormal somatic features including coarse faces, broad nasal root, thick lips, deafness, delayed bone age, pectus carinatum, scoliosis, short rib cage, and dysostosis multiplex. Other clinical features include lipidosis, sulfatidosis, macular pigmentary abnormality, movement disorder, dwarfism, speech defect, splenomegaly, and storage liver disease.

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Chest radiographs and resting oxygen saturation must be obtained in view of frequent respiratory infections/obstructive sleep apnea. Abnormal airway with macroglossia, thickened mucosal folds in oro and naso-pharynx, together with skeletal deformities. Liver function tests and coagulation profiles if hepatomegaly is present.

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Airway management will be a major challenge with or without endotracheal intubation. Loss of muscle tone after general anesthesia induction results in upper airway obstruction. It is recommended to have a laryngeal mask airway available in case of failure to ventilate with face-mask or intubate the trachea. Patient positioning in the presence of contractures can be difficult. Chronic pulmonary infections and kyphoscoliosis can lead to postoperative respiratory failure.

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Avoid the use of muscle relaxants if possible until the trachea is intubated and lung ventilation is confirmed. The use of opioids should also be prudent in the presence of sleep apnea and mental retardation.

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There are three other categories of genetic neurodegenerative disorders that can be distinguished from one another based on head CT scan, head MRI, nerve conduction velocities, visually evoked potentials, auditory evoked potentials, electroretinography, and, to a lesser extent, electroencephalography. The ultimate diagnosis is obtained from skin, conjunctival, and nerve biopsies.

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Sphingolipidoses: This category includes six specific diseases: Niemann-Pick Disease; Gaucher Disease; Krabbe Disease (Globoid Cell Leukodystrophy) and Metachromatic Leukodystrophy; GM1-Gangliosidosis and GM2-Gangliosidosis. The common features of all these entities is the ability to destroy storage of fats within nerve cells.

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