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HEREDITARY MONOGENIC DISEASES

           

Glycogen type 2 or Pompe disease

Pompe disease or glycogenosis type 2 is a hereditary metabolic illness that consists of a congenital deficiency of the enzyme alpha 1, 4-glucosidase. The enzyme degrades alpha -1,4 and alpha -1,6 linkages in glycogen, maltose, and isomaltose. Deficiency of the enzyme results in accumulation of glycogen within lysosomes and in cytoplasm eventually leading to tissue destruction if treatment is not applied early.

Glycogen storage disease due to acid maltase deficiency (AMD) is an autosomal recessive trait leading to metabolic myopathy that affects cardiac and respiratory muscles in addition to skeletal muscle and other tissues. AMD represents a wide spectrum of clinical presentations caused by an accumulation of glycogen in lysosomes: Glycogen storage disease due to acid maltase deficiency, infantile onset, non-classic infantile onset and adult onset. Early onset forms are more severe and often fatal.

Pompe disease is an autosomal recessive condition—meaning that each parent of an affected individual must pass on a copy of the mutated gene. This is part of the reason that the disease is relatively rare, affecting 1 in 40,000 people.

SIGNS AND SYMPTOMS

Pompe disease represents a wide spectrum of clinical presentations caused by an accumulation of glycogen in lysosomes: Glycogen storage disease due to acid maltase deficiency, infantile onset, non-classic infantile onset and adult onset. Early onset forms are more severe and often fatal.

  • Infantile onset: begins within a few months of birth. In the absence of enzymatic substitution treatment, infants with this form of Pompe disease die from heart failure in the first year of life.

Although each patient can present individual peculiarities, the most characteristic symptoms are muscle weakness (myopathy), poor muscle tone (hypotonia), an enlarged liver (hepatomegaly), and heart defects. Affected infants may also fail to gain weight and grow at the expected rate (failure to thrive) and have breathing problems.

  • Non-classic form of infantile-onset Pompe disease usually appears by age 1. It is characterized by delayed motor skills (such as rolling over and sitting) and progressive muscle weakness. The heart may be abnormally large (cardiomegaly), but affected individuals usually do not experience heart failure. The muscle weakness in this disorder leads to serious breathing problems, and most children with non-classic infantile-onset Pompe disease live only into early childhood.

The late-onset type of Pompe disease may not become apparent until later in childhood, adolescence, or adulthood. Late-onset Pompe disease is usually milder than the infantile-onset forms of this disorder and is less likely to involve the heart. Most individuals with late-onset Pompe disease experience progressive muscle weakness, especially in the legs and the trunk, including the muscles that control breathing. As the disorder progresses, breathing problems can lead to respiratory failure.

PREVENTION

Because it is a hereditary disorder, there are no effective preventive measures. Persons with a family history of this illness should seek genetic counseling.

GENE OR REGION STUDIED


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