Acid Maltase Deficiency

From WikiGenetics

1 Name of Condition
2 Definition
3 Description, Signs and Symptoms
4 Inheritance
5 Diagnosis
6 Treatment and Management
7 Prognosis
8 Resources
9 References

[edit] Name of Condition

Acid Maltase Deficiency (AMD); also called glycogen storage disease type II or Pompe disease.

[edit] Definition

Acid Maltase Deficiency is a rare, autosomal recessive metabolic disorder that is a result of a lack in the enzyme acid maltase, which is necessary for the break down of glycogen, a stored form of sugar used for energy.

[edit] Description, Signs and Symptoms

The excessive accumulation of glycogen due to this condition results in progressive muscle weakness (myopathy) all throughout the body and affecting major body tissues in the heart, skeletal muscles, liver and nervous system.

There are different forms of AMD which present varying signs and symptoms: Infantile AMD (Pompe disease)

early hypotonia
severe cardiac and respiratory complications
severe lack of muscle tone
enlarged liver and heart
mental retardation
difficulty swallowing

Juvenile AMD

Motor delays
Progressive myopathy
predominantly involving skeletal muscle
progressive weakness and respiratory failure

Adult AMD

typical onset occurs in second and third decade of life
progressive weakness and degeneration of respiratory muscles in the trunk, legs, and diaphragm

The heart, liver, and central nervous system are less involved in the juvenile and adult manifestations of AMD.

[edit] Inheritance

In is an autosomal recessive metabolic disorder, meaning that two copies of the mutated gene (one from each parent) must be inherited to have this condition. There is a 25% chance of a child being born with AMD if both parents are carriers of the defective gene. It is estimated that AMD occurs in about 1 in 40,000-300,000 births.

[edit] Diagnosis

Diagnosis can be made by:

prenatal diagnosis using chorionic villi sampling or amniocentesis used for the infantile form (Pompe disease) where abnormally low levels of acid maltase can be detected in the serum
newborn screening for Pomp disease can determine the total acid alpha-glucosidase present in plasma.
muscle biopsy
enzyme assay on the tissue concentration level of acid maltase
chest radiographs to reveal an enlarged heart, electrocardiographs

[edit] Treatment and Management

Complications associated with AMD are treated symptomatically and physical therapy programs are available for patients and may be beneficial. The first treatment for patients with Pompe disease, known as Myozyme, was developed and approved by the US Food and Drug Administration in 2006. Myozyme is a recombinant variety of the human enzyme acid alpha-glucosidase and helps with the break down of glycogen.

[edit] Prognosis

The prognosis for patients with Pompe disease varies symptomatically, however, without treatment, the disease can be lethal during infancy and early childhood. Treatment with Myozyme in enzyme replacement therapy has had positive outcomes in prolonging ventilator-free survival rates and has the potential to decrease mortality and disability rates associated with infantile AMD.