Glycogen storage disease type II

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Glycogen storage disease type II (also called Pompe disease or acid maltase deficiency) is a neuromuscular, autosomal recessive metabolic disorder in the family of lysosomal storage diseases caused by a deficiency in the enzyme acid maltase (EC 3.2.1.20), which is needed to break down maltose, a stored form of sugar used for energy. Maltose is a disaccharide formed when amylase breaks down glycogen, a long, branched glucose polymer. It is the only glycogen storage disease with a defect in lysosomal metabolism, and was the first glycogen storage disease to be identified, in 1932.

The build-up of glycogen causes progressive muscle weakness (myopathy) throughout the body and affects various body tissues, particularly in the heart, skeletal muscles, liver and nervous system.

The disease is named after Johann Pompe, who characterized it in 1932.[1][2]

The disorder is estimated to occur in about 1 in 40,000-300,000 births.

It has an autosomal recessive inheritance pattern. This means the defective gene is located on an autosome, and two copies of the gene – one from each parent – are required to be born with the disorder. As with all cases of autosomal recessive inheritance, children have a 1 in 4 chance of inheriting the disorder when both parents carry the defective gene, and although both parents carry one copy of the defective gene, they are usually not affected by the disorder.

Pompe disease has historically been divided into three forms defined by age of onset and progression of symptoms (see below). More recently there has been a trend to divide the disease into two groups: infantile onset (involving the massive enlargement of the heart) and late onset (no heart enlargement):

Infantile, or early onset, is noticed shortly after birth. Symptoms include severe lack of muscle tone, weakness, and enlarged liver (hepatomegaly) and heart. Mental function is not affected. Development appears normal for the first weeks or months but slowly declines as the disease progresses. Swallowing may become difficult and the tongue may protrude and become enlarged. Most children die from respiratory or cardiac complications before 2 years of age.

Juvenile onset symptoms appear in early to late childhood and include progressive weakness of respiratory muscles in the trunk, diaphragm and lower limbs, as well as exercise intolerance. Intelligence is normal.

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