Glycogenosis type 2 or Pompe disease

Pompe disease or glycogenosis type 2 is the first lysosomal storage disorder to be discovered and belongs to a group of diseases that currently includes more than 50 pathologies. In Pompe disease the GAA gene coding for the lysosomal enzyme acid alpha-glucosidase, which is involved in glycogen metabolism, is altered.

A deficiency in acid alpha-glucosidase can have different consequences on tissues, although for this type of glycogenosis the most notable effect occurs in muscle tissue cells. Deficiency in this enzyme produces a gradual accumulation of glycogen in the lysosomes of muscle cells, which can rupture, causing irreversible damage to the muscle.

The frequency of Pompe disease is approximately 1 case per 40,000 live births, although the incidence may be higher.

There are three clinical presentations of Pompe disease which are determined by the residual enzymatic activity of acid alpha-glucosidase:

• Infantile or classic: this is the most severe and symptoms usually appear from the second month of life onwards. The disease progresses very rapidly and glycogen is deposited mainly in skeletal muscle and in the heart, causing cardiomyopathy, hypotonia and difficulty in feeding and breathing, among other symptoms. If untreated, it is very difficult for these children to survive beyond one year of life.
• Juvenile: a first symptom is the difficulty in reaching age-appropriate motor skills in time. The trunk and lower limbs become firm to the touch, scoliosis, contractures and ligament shortening may occur. As the disease progresses, respiratory insufficiency appears.
• Adult or late-onset: slowly progresses as a progressive myopathy leading to respiratory failure.

Enzyme replacement therapy with recombinant human acid alpha-glucosidase (rhGAA, MyozymeR®) is the treatment used to improve the symptomatology of patients with Pompe disease since 2006. MyozymeR® is a drug that is administered venously and provides the enzyme acid alpha-glucosidase artificially.