Mucolipidosis type II

It belongs to a group of metabolic diseases that affect the production or function of lysosomal enzymes. It is characterized by mental retardation and alterations in bone development.

Mucolipidoses are a group of diseases affecting lysosomal storage in which the enzymes that act in the lysosome are disrupted. When these enzymes do not function properly, cells are unable to break down certain substances, such as carbohydrates and lipids, resulting in accumulations that induce cell and tissue damage in multiple organs.

Mucolipidoses are classified into 4 types according to the lysosomal enzyme that is affected. Type II mucolipidosis is caused by a deficiency of the enzyme N-acetylglucosamine-1-phosphotransferase, which is caused by pathogenic variants in the GNPTAB gene.

The prevalence of type II mucolipidosis is approximately 1 case per 1,000,000 people, although it may be higher in certain geographic areas such as the Saguenay-Lac-Saint-Jean region of Quebec.

Symptoms

In type II mucolipidosis patients present with physical signs from birth such as abnormal skeletal development, characteristic facial features, restricted joint movement and delayed motor development. On the other hand, there is an enlargement of vital organs such as the liver, spleen or mitral and aortic heart valves. As for the respiratory system, there is a thickening of the mucosa and a stiffening of the connective tissues leading to respiratory insufficiency and infections. Most patients do not survive beyond early childhood.

Disease management

There is no cure for this disease and treatment is palliative. There are programs that stimulate cognitive development and they are also monitored to control respiratory and cardiac functions. In some cases, respiratory assistance or assisted ventilation is necessary.

Genes analyzed

GNPTAB

Bibliography

Khan SA, Tomatsu SC. Mucolipidoses Overview: Past, Present, and Future. Int J Mol Sci. 2020 Sep 17;21(18):6812.

Paik KH, Song SM, Ki CS, et al. Identification of mutations in the GNPTA (MGC4170) gene coding for GlcNAc-phosphotransferase alpha/beta subunits in Korean patients with mucolipidosis type II or type IIIA. Hum Mutat. 2005 Oct;26(4):308-14.

Velho RV, De Pace R, Klünder S, et al. Analyses of disease-related GNPTAB mutations define a novel GlcNAc-1-phosphotransferase interaction domain and an alternative site-1 protease cleavage site. Hum Mol Genet. 2015 Jun 15;24(12):3497-505.