Maple Syrup Urine Disease (MSUD) is an amino acid disorder. It is a hereditary disease that is caused by a missing enzyme needed to digest the branched-chain amino acids (leucine, isoleucine, and valine) found in protein. These amino acids build-up in the blood and are toxic to the brain.
The gene defect for MSUD is inherited when both parents have the same abnormal gene and unknowingly pass it on to their baby. A parent who has the abnormal gene, but not the disease, is called a carrier. The health of a carrier is rarely affected. However, for each pregnancy of two such carriers, there is a 1 in 4 chance that the child will be born with the disease. MSUD occurs in about 1 in every 100,000 births in Australia.
MSUD causes problems very early in the newborn period, such as poor feeding, lethargy, convulsions, and coma. If not treated, the disease soon leads to death. The infant's urine has a sweet maple syrup smell, which gives the disease its name. As with all hereditary disorders, there are some less severe forms, the mildest of which may go undetected for months or years.
With MSUD, early assessment and treatment are important and infants may need intensive care for a few days. A low-protein diet with a formula free of branched-chain amino acids is also needed. The special diet must be maintained throughout life.
Detection can depend on the amount of protein ingested by the infant. Mild forms of MSUD may also be missed as the blood levels of branched-chain amino acids may not be increased in the first weeks of life.