Definition of Maple syrup urine disease:

Maple syrup urine disease (MSUD) is a metabolism disorder passed down through families in which the body cannot break down certain parts of proteins. Urine in persons with this condition smells like maple syrup.

Causes, incidence, and risk factors:

Maple syrup urine disease (MSUD) is caused by a gene defect. Persons with this condition cannot break down the branched-chain amino acids leucine, isoleucine, and valine. This leads to a build-up of these chemicals in the blood.

In the most severe form, MSUD can damage the brain during times of physical stress (such as infection, fever, or not eating for a long time).

MSUD also occurs in an intermittent form and a mild form. Even in the mildest form, infections can cause mental retardation and high levels of leucine.