Sialidosis

Mucolipidosis type I(ML I) is an inheritedlysosomal storage diseasethat results from a deficiency of the enzyme alpha-N -acetylneuraminidase(sialidase).The lack of thisenzymeresults in an abnormal accumulation of complex carbohydrates known asmucopolysaccharides,and of fatty substances known asmucolipids.Both of these substances accumulate in bodily tissues.

Sialidosis
Other names	Sialidosis
Sialic acid
Specialty	Endocrinology

Presentation

Symptoms of ML I are either present at birth or develop within the first year of life. In many infants with ML I, excessive swelling throughout the body is noted at birth. These infants are often born withcoarse facial features,such as a flat nasal bridge, puffy eyelids, enlargement of the gums, and excessive tongue size (macroglossia). Many infants with ML I are also born with skeletal malformations such aship dislocation.Infants often develop sudden involuntary muscle contractions (calledmyoclonus) and have red spots in their eyes (cherry red spots). They are often unable to coordinate voluntary movement (calledataxia).Tremors,impaired vision, andseizuresalso occur in children with ML I. Tests reveal abnormal enlargement of the liver (hepatomegaly) and spleen (splenomegaly) and extreme abdominal swelling. Infants with ML I generally lack muscle tone (hypotonia) and have mental retardation that is either initially or progressively severe. Many patients suffer from failure to thrive and from recurrentrespiratoryinfections. Most infants with ML I die before the age of one year.

Related conditions

Other diseases that result from a deficiency in the sialidase enzyme are categorized in a broader group known as sialidoses. Because ML I is classified as a sialidosis, it is sometimes referred to as sialidosis type II.

A rarer form of sialidosis – sialidosis type 1 – occurs in children and adolescents and is often referred to as the juvenile form of the disorder. Children usually begin to show symptoms during the second decade of life, and myoclonus and cherry-red macules are often the initial symptoms. Patients usually develop seizures and progressive deterioration of coordinated muscular and mental activities.

Pathophysiology

The role ofsialidaseis to remove a particular form ofsialic acid(a sugar molecule) from sugar-protein complexes (referred to asglycoproteins), which allows the cell to function properly. Because the enzyme is deficient, small chains containing the sugar-like material accumulate inneurons,bone marrow, and various cells that defend the body againstinfection.

Diagnosis

The detection of high urinary sialyl oligosaccharides and the confirmation of lysosomal enzyme deficiency in leukocytes or cultured fibroblasts make the diagnosis.

Management

Treatment of sialidosis is similar to the otherprogressive myoclonic epilepsydisorders, which consists of managing seizures and myoclonus along with palliative, supportive, and rehabilitative care.

See also

• Fucosidosis
• Mucolipidosis

References

• mucolipidosesatNINDS- article derived from detail sheet available here

External links

• Sialidosis type 1 and 3atNIH's Office ofRare Diseases
• SialidosisatNIH's Office ofRare Diseases