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California Newborn Screening Program

Maple Syrup Urine Disease (MSUD)

What is MSUD?

MSUD stands for "maple syrup urine disease". It's named for the sweet maple syrup smell of the urine in untreated babies. It is one type of amino acid disorder. People with this type of disorder have problems breaking down amino acids from the protein in the food they eat. The group of enzymes called "branched-chain ketoacid dehydrogenase" are either missing or not working properly. This group of enzymes breaks down three different amino acids, leucine, isoleucine, and valine. These amino acids are "branched-chain amino acids" (BCAA) and are found in all foods that have protein. When the enzymes are missing or not working properly, these amino acids can't be broken down and build up in the blood.

What are the symptoms?

Some of the first symptoms are poor appetite, weight loss, a high pitched cry, and urine that smells like maple syrup or burnt sugar. Babies with MSUD can have a type of illness called a metabolic crisis. The symptoms of a metabolic crisis are extreme sleepiness, sluggishness, irritable mood, and vomiting. A metabolic crisis can be caused by going too long without food, an illness or infection, or stressful events like surgery. If not treated, a metabolic crisis can cause other more serious symptoms including swelling of the brain, seizures, and coma, sometimes leading to death. Untreated MSUD can also cause mental retardation, blindness, and even death.

What is the treatment?

The baby's primary doctor will work with a metabolic specialist and a dietician familiar with MSUD to develop an individual treatment plan for the baby. Treatment can include:

  • Medical formula - Even though people with MSUD can't break down protein, they still need the parts of protein the body uses on a daily basis. A special medical formula provides the nutrients needed in a form that they can use while limiting the amount of harmful branched-chain amino acids.
  • A low protein food plan - A diet that limits the amount of branched-chain amino acids, which are found in protein, is recommended. This means that foods that are high in protein, like cow's milk, regular formula, meat, fish, eggs, and cheese, should be avoided. Regular flour, dried beans, nuts, and peanut butter should also be avoided or strictly limited. Many fruits and vegetables are low in branched-chain amino acids and can be eaten in carefully measured amounts.
  • Tracking BCAA levels - Regular blood tests to track the amino acid levels in the blood are necessary. This way, the treatment can be adjusted for each individual's needs, keeping levels in the desired range.
  • Supplements - Sometimes thiamine supplements are given.

Parents' Guide to MSUD (PDF)

Last modified on: 8/24/2010 3:07 PM