Definition:
I-Cell disease results from deficiency of several lysosomal enzymes. The genes’ coding for these enzymes are normal. The enzymes are normally translated, but are not normally transported to the lysosomes from the endoplasmic reticulum because they lack a specific targeting signal. Without the proper functioning of N-acetylglucosamine-1-phototransferase, a build up of these substances occur when enzymes are unable to travel inside of the lysosome. These substances accumulate into masses, referred to as inclusion bodies, inside the lysosome, and can be seen under a microscope when a diagnosis for the disorder is trying to be made.

There are two forms of I-Cell disease/Mucolipidosis: Type II and Type III. Together they affect one in 325,000 live births worldwide.

Symptoms:
Typically, by the age of 6 months, failure to thrive and developmental delay are obvious symptoms of this disorder. Other symptoms include coarse facial features, skeletal problems, and stiff claw-shaped hands. Carpal tunnel syndrome pain and loss of sensation in the fingertips are common. Hernias, enlarged liver and spleen, a thickening and weakening of the heart muscle, chronic ear infections, and corneal clouding are also present. Additional symptoms are poorly and late formed teeth, as well as a dental condition called gingival hyperplasia, in which the gums are very prominent.

Inheritance Pattern:
I-Cell disease/Mucolipidosis II is an autosomal recessive disorder.

Life Expectancy:
Life expectancy for I-Cell disease/Mucolipidosis II disease is younger than five years of age.

Diagnosis and Testing:
An enzyme assay which measures the amount of N-acetylglucosamine-1-phototransferase typically confirms a diagnosis. White blood cells are examined to measure the amount of this enzyme. If they are low in comparison to normal standards for N-acetylglucosamine-1-phototransferase, a diagnosis of this disorder can be made. A skin biopsy can also be performed which measures the same enzyme in a cultured tissue sample. Low levels of N-acetylglucosamine-1-phototransferase found in comparison to normal standards confirm a diagnosis.

The gene responsible for this disorder has been identified, rendering accurate diagnosis, prenatal diagnosis, and carrier testing to be possible.

Treatment:
There is no cure for I-Cell disease/Mucolipidosis II disease. Treatment is limited to controlling or reducing the symptoms that are associated with this disorder. Nutrition supplements, particularly iron and vitamin B12, are often recommended for individuals with I-Cell disease. Physical therapy to improve motor delays and speech therapy to improve language acquisition are treatment options. Surgery can remove the thin layer of corneal clouding to temporarily improve the complication.

Patient Groups:
International Society for Mannosidosis & Related Diseases
P.O. Box 328
Dexter, MI 48130
www.mannosidosis.org
tel: (734) 449-8222
fax: (734) 449-2282
Terri Klein, Executive Director
info@ismrd.org