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.
Sialidosis type I: Cherry-Red-Spot, Myoclonus Syndrome
Sialidosis type II: Mucolipidosis type I; Sialidase Deficiency; Glycoprotein Neuraminidase Deficiency; NEUG Deficiency; Lipomucopolysaccharidosis.
Genetic disorder with a 2.5:1 male preponderance.
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
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.
Excessive urinary oligosaccharides can be demonstrated.
Definitive diagnosis is based on sialidase activity present in tissue
samples (e.g., fibroblasts, WBCs).
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
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.
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
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.
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.
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