Maple Syrup Urine Disease (MSUD) is an inherited metabolic disorder, that, if untreated, causes mental retardation, physical disabilities and death. First described as a disease in 1954, it is a rare disorder, believed to be in all ethnic groups worldwide. The national incidence is 1 in 225,000 births.

MSUD derives its name from the sweet, burnt sugar, or maple syrup smell of the urine. The disorder affects the way the body metabolizes (processes) certain components of protein. These components are the three branched-chain amino acids leucine, isoleucine, and valine. These amino acids accumulate in the blood causing a toxic effect that interferes with brain functions.

Types and Symptoms
The term, Maple Syrup Urine Disease, includes a range of classic and variant types of the disorder. The symptoms of classic MSUD are usually evident within the first week of life. Variant forms of MSUD are milder, however, the symptoms can be severe during times of illness.
The first symptoms in an infant are poor appetite, irritability, and the characteristic odor of the urine. Within days they lose their sucking reflex and grow listless, have a high-pitched cry, and become limp with episodes of rigidity. Without diagnosis and treatment, symptoms progress rapidly to seizures, coma, and death. In some variant types, failure to thrive may be the first sign. The earlier these children are diagnosed and treated, the less risk of permanent damage.

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Testing for MSUD
Some states test for MSUD in their newborn screening programs. MSUD should be included in all screening programs. Ideally each infant should be tested within 24 hours of birth and the test results available by two to three days of age. This should be the goal of all testing for MSUD. Early diagnosis is of paramount importance for the child with MSUD to develop normally.
Unfortunately some variant types of MSUD may be missed with screening programs. However, any child at risk or suspected of having MSUD should be tested. If the result is positive, or suspected to be positive, treatment should be started immediately.

Testing to identify carriers is only available for the Mennonite classic type of MSUD. The Mennonite population from eastern Pennsylvania is at high risk for this classic form of the disorder.

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Treatment
Treatment of children with MSUD must be started as soon as possible, preferably at birth. It involves a complex approach of maintaining metabolic control. A special, carefully controlled diet is the focus of daily treatment. This requires careful monitoring of protein intake and close medical supervision.

The diet centers around a synthetic formula or "medical food" which provides nutrients and all the amino acids except leucine, isoleucine and valine. These three amino acids are added to the diet with carefully controlled amounts of food to provide the protein necessary for normal growth and development without exceeding the level of tolerance.

Various tests are available to monitor the levels of the amino acids and their keto acid derivatives in the blood and urine. Illnesses and stress, as well as consuming too much protein, raise these levels. Even mild illnesses can become life‑threatening. A metabolic imbalance requires dietary changes and at times hospitalization.

Each parent of a child with MSUD carries a defective gene for MSUD along with a normal gene. The defective gene is a recessive gene, therefore parents are called "carriers" and are not affected by the disease. Each child receives one gene from each parent.

When both parents are carriers, there is a 1 in 4 chance with each pregnancy that the baby will receive a defective gene from each parent and have MSUD; a 2 in 4 chance the baby will receive one defective and one normal gene becoming a carrier of MSUD; and a 1 in 4 chance the baby will receive two normal genes. Persons with two normal genes cannot pass MSUD to their offspring.

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* If you are interested in learning more about MSUD, please visit the MSUD Support Group. This is a wonderful group, which can put you in contact with individuals and families living with MSUD around the world. They provide a Quarterly newsletter with updates on issues relevant to MSUD as well as running an email group to discuss any questions or issues you may have. the MSUD support group also sponsors a symposium once every 2 years, in which families come together with medical professionals to learn more about new developments in care and research. 

© 2003-2005 MSUD Research Foundation - PO Box 2512 - Gilbert, Arizona 85299
Phone: (480) 279-1018 or (480) 813-8209 - Fax: (602) 276-7522