What is Enzyme Replacement Therapy?

Enzyme replacement therapy is a type of treatment for a variety of diseases. The name is fairly clear: enzymes are introduced into the body artificially to compensate for some deficiency. Enzyme replacement therapy is used as a treatment for Gaucher's disease, Fabry disease, Glycogen storage disease type II, cystic fibrosis and others. Usually, fresh enzymes must be injected regularly for the therapy to work.

An enzyme is a protein used by the body to catalyze, or make possible, a specific chemical reaction. Enzymes have one or more binding sites that are set up to receive a certain type of molecule and perform some type of operation on it. For example, there are many different enzymes in saliva that are structured so that they can break down food.

If the body does not have enough of a certain type of enzyme, the reaction for which that enzyme is responsible may not take place at an appropriate rate. The most common way for an enzyme deficiency to occur is through a genetic mutation. Some, although not all, genetic mutations can change the structure of the protein being expressed from the mutated gene. If this occurs, the body may be producing an enzyme, but not one that causes the necessary reaction. This is where enzyme replacement therapy comes in.

Enzyme replacement therapy usually introduces approximately the same enzyme that is lacking in the body from the outside. For example, Gaucher's disease is caused by a deficiency of glucocerebrosidase, an enzyme which plays an important role in the body's metabolism. The disease can be treated with injections of imiglucerase, a synthetic analog produced by Genzyme.

A second type of enzyme replacement therapy introduces enzymes that have become deficient for some other reason. Cystic fibrosis is caused by the body's failure to produce a particular protein that is crucial to the function of cell membranes. The disease cannot be cured simply by injecting this protein into the body; it would not function correctly.

Enzyme replacement therapy, however, can correct a symptom of cystic fibrosis. The disease causes problems with pancreatic ducts, which prevent enzymes from entering the gastrointestinal tract in order to digest food. Enzyme replacement therapy can introduce a variety of digestive enzymes in order to correct this secondary problem.

Enzyme replacement therapy is a relatively new type of treatment. As more is discovered about the genome and about the cellular function of proteins, new forms of enzyme replacement therapy are likely to emerge. This treatment is expensive, however, since it requires the external synthesis of proteins and is necessarily ongoing. In the natural course of operations, proteins degrade and are reproduced. Normally this degradation helps the organism to regulate itself, but for enzyme replacement therapy, the implication is that fresh injections of the enzyme are needed almost every week.