Lysosomal Storage Diseases: How is Pompe Disease Classified?

Pompe disease is a lysosomal storage disease (LSD) because, like other LSDs, it interferes with the body’s ability to break down molecules inside the lysosomes, which are compartments inside the cell.

Pompe disease is also classified as: A metabolic muscle disease because it shares the symptoms of progressive muscle

weakness and loss of muscle tissue (muscle wasting) with many different neuromuscular disorders (including muscular dystrophies).

A glycogen storage disease because Pompe disease causes glycogen to build up in the lysosomes of muscle cells.

LSDs are a group of more than 40 genetic disorders caused by inborn errors of metabolism (which are problems in the genes that affect how cells break down certain molecules). People with LSDs are either lacking or in short supply of particular enzymes that are found in the lysosome (a special compartment of the cell). Because of this, molecules that are meant to be broken down by the missing enzymes build up within the lysosome, and can prevent the cell from working properly.

Separately, lysosomal storage diseases are each rare diseases. As a group, lysosomal storage diseases are estimated to affect 1 in 7,700 live births. Most lysosomal storage diseases are progressive and life threatening. Living with a lysosomal storage disease means living with a rare disease that is sometimes not well understood.

Examples of lysosomal storage diseases include: * Batten disease * Fabry disease * Gaucher disease * Krabbe disease * Mucopolysacchiradosis I (MPS I/Hurler/Hurler-Scheie/Scheie) * Mucopolysacchiradosis II (MPS II/Hunter Disease) * Niemann-Pick disease * Pompe disease * Tay-Sachs disease

Most LSDs have an autosomal recessive inheritance pattern, which means that in order for a person to develop the disease, that person must inherit two copies of the abnormal gene, one from each parent. Gaucher disease, MPS I, Pompe disease, and Niemann-Pick disease are all autosomal recessive.

Genetic counseling can help families understand the chance of passing on the disease to children and can help people living with lysosomal storage diseases make informed decisions about family planning.

The cell is the smallest basic unit of life that performs the functions needed to exist: * Respiration (“breathing” for the cell) * Consumption of nutrients (“digestion” for the cell) * Processing of metabolic wastes (“waste removal” from the cell)

The lysosome is a critical compartment within the cell. The lysosome digests extra materials and food within the cell, breaking down molecules with strong enzymes. These enzymes are so strong and destructive that they are contained in the lysosome, a separate, membrane-bound section of the cell.

The lysosome "digests" molecules taken in by the cell. The lysosome breaks down molecules that are taken in by the cell in order to give the cell the building blocks it needs to grow and divide. These building blocks are pumped across the lysosome's membrane (outer surface) to the inside of the cell, where they are used to build new structures that allow the cell to function correctly. The process by which the cell takes in and breaks down materials is like the "digestive tract" of the cell.

Specific enzymes break down specific types of molecules. Each class of molecule taken into the lysosome has a set of lysosomal enzymes that will break the molecules down into the building blocks the cell will use to create new molecules. There is a fine balance between the creation (or synthesis) of one set of molecules and the breakdown (or degradation) of another set of molecules.

Undigested material will build up in the lysosome. Lysosomes must be very efficient in digesting the full range of materials brought into the cell. Any material that cannot be digested will generally build up in the lysosome and may clog up other cellular processes. Lysosomal storage diseases are caused by a genetic defect that interferes with the breakdown of materials in the lysosomal system, which may cause severe problems for patients.

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DISCUSSION QUESTIONS

1. What is Pompe disease?2. How do most LSDs affect people?3. Choose 1 of the LSD diseases and research the causes, symptoms, and treatment for the disease.