Maple syrup urine disease (MSUD) is an inherited disorder characterized by impaired protein metabolism, specifically the branched chain amino acids leucine, isoleucine, and valine. The condition gets its name from the distinctive sweet odor of urine and earwax in affected infants. If untreated, MSUD can lead to developmental delays, seizures, coma, and death.
MSUD is a rare disease, affecting an estimated 1 in 185,000 infants worldwide. While pan-ethnic and found world-wide, the disorder occurs much more frequently in certain ethnic groups, such as the Old Order Mennonite population with an estimated incidence of about 1 in 380 newborns, and the Ashkenazi Jewish population with an estimated incidence of 1 in 26,000 newborns.
MSUD was first described in 1954 and identified as an error in branched-chain amino acid metabolism in 1957. The life-saving metabolic formula was developed in the 1960’s, allowing survival for the first time. The formula provides all essential nutrients with the exception of the branched-chain amino acids leucine, isoleucine, and valine. These must be added to the diet in the precise amounts needed for normal growth and development. A strict diet and careful medical monitoring is essential throughout the lifespan. With proper care, individuals with MSUD now live relatively normal and productive lives.