Maple Syrup Urine Disease (MSUD) is a disorder in the body's ability to use three of the essential amino acids in protein. These three essential amino acids-leucine, isoleucine and valine-are often called the branched-chain amino acids (BCAAs).

Protein in the body is made up of 20 amino acids; eleven of these are essential, and nine are nonessential. The essential amino acids must be supplied in the daily diet. The nonessential amino acids can be obtained from the diet or produced in the body from other amino acids.

In MSUD, the enzymes necessary to break down leucine, isoleucine and valine are either absent, inactive, or only partially active. Because of the enzyme deficiency in MSUD, the BCAAs and their byproducts (called ketoacids) become elevated. It is these elevations that cause an infant or child with MSUD to become symptomatic.


MSUD is a serious disorder with life-threatening consequences unless addressed promptly. However, MSUD is manageable, just as diabetes is manageable. Careful monitoring and adherence to dietary restrictions are essential. Even minor illnesses and infections must be taken seriously and require special care. Treatment for MSUD has improved greatly over the past few years. It is of utmost importance that all children who have MSUD receive the benefit of the most up-to-date treatment.

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The information presented on this web site is for educational purposes. It does not replace medical consultation. The MSUD (Maple Syrup Urine Disease) Family Support Group is not liable for the application of this information or any errors therein.

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