Mucolipidosis II alpha/beta (I-Cell Disease)
Mucolipidosis II alpha/beta (also known as I-Cell Disease) is a progressively debilitating disorder that affects many parts of the body and is caused by mutations in the GNPTAB gene. This gene provides instructions for making part of an enzyme called GlcNAc-1-phosphotransferase. Mutations in the GNPTAB gene that cause mucolipidosis II alpha/beta prevent the production of any functional GlcNAc-1-phosphotransferase
At birth, children with mucolipidosis II alpha/beta are small and have weak muscle tone (hypotonia) and a weak cry. Affected individuals grow slowly after birth and usually stop growing during the second year of life. Development is delayed, particularly the development of speech and motor skills such as sitting and standing.
Children with mucolipidosis II alpha/beta typically have several bone abnormalities, many of which are present at birth. Affected individuals may have an abnormally rounded upper back (kyphosis), feet that are abnormally rotated (clubfeet), dislocated hips, unusually shaped long bones, and short hands and fingers. People with this condition also have joint deformities (contractures) that significantly affect mobility. Most children with mucolipidosis II alpha/beta do not develop the ability to walk independently. Affected individuals have dysostosis multiplex, which refers to multiple skeletal abnormalities seen on x-ray.
Other features of mucolipidosis II alpha/beta include a soft out-pouching around the belly-button (umbilical hernia) or lower abdomen (inguinal hernia), heart valve abnormalities, distinctive-looking facial features that are described as "coarse," and overgrowth of the gums (gingival hypertrophy). Vocal cords can stiffen, resulting in a hoarse voice. The airway is narrow, which can contribute to prolonged or recurrent respiratory infections. Affected individuals may also have recurrent ear infections, which can lead to hearing loss.
How common is mucolipidosis II alpha/beta?
Mucolipidosis II alpha/beta is a rare disorder, although its exact prevalence is unknown. It is estimated to occur in about 1 in 100,000 to 400,000 individuals worldwide.
Medical and Research Information
- GeneReviews: Gives good descriptions of genetic diseases. Information is comprehensive, and access is free to all users.
- Genetic Home Reference: An excellent description of Mucolipidosis II alpha/beta
- GeneTests: List of laboratories testing for Mucolipidosis II.
- Clinical Trials Registry of federally and privately supported clinical trials conducted in the United States and around the world. This site gives information about each trial’s purpose, who may participate and the location.
- OMIM: Technical information about the genetics of Mucolipidosis II. OMIM is a site developed for scientists and medical specialists and contains both general and highly technical information. Access to this site is free.
Patient Support Groups
- ISMRD: The International Advocate for Glycoprotein Storage Diseases is the international support group for Mucolipidosis II.
- LDNZ: Lysosomal Diseases New Zealand is the support group for families in New Zealand