Maple syrup urine disease (MSUD), also known as branched-chain ketoaciduria, is a rare and inherited metabolic disorder that affects the breakdown of certain amino acids in the body. This condition is named after the distinctive sweet odour of the urine, which resembles the smell of maple syrup or burnt sugar.

MSUD is caused by a deficiency in one of the enzymes (branched-chain alpha-ketoacid dehydrogenase complex; BCKD) required to break down three essential amino acids: leucine, isoleucine, and valine. These amino acids are obtained from protein-containing foods and are crucial for normal growth and development. In individuals with MSUD, the impaired enzyme function leads to the accumulation of toxic by-products, including branched-chain alpha-keto acids, causing a range of neurological and physical symptoms. 

Symptoms of MSUD typically appear shortly after birth, as new borns begin to consume protein in breast milk or formula. The severity of symptoms can vary widely depending on the individual and the specific genetic mutation involved. Common symptoms of MSUD include Sweet-smelling urine (often described as smelling like maple syrup), Poor feeding and lack of appetite, vomiting, lethargy and irritability, developmental delays, Seizures and Coma (in severe cases).  If left untreated, MSUD can lead to irreversible brain damage and death.

The diagnosis of MSUD is often confirmed through new born screening, which allows for early detection and intervention. A blood test is performed to measure the levels of amino acids and their metabolites. Elevated levels of leucine, isoleucine, and valine, along with characteristic changes in other amino acids, can indicate the presence of MSUD.

Treatment involves a strict and carefully controlled diet that limits the intake of leucine, isoleucine and valine. This dietary management aims to prevent the accumulation of toxic substances and minimize the risk of neurological damage. In some cases, individuals with MSUD may also require special medical formulas or supplements to ensure proper nutrition. Regular monitoring of blood amino acid levels is essential to adjust treatment as needed and prevent metabolic crises. In some cases, liver transplantation may be considered as a treatment option for individuals with severe MSUD who do not respond well to dietary therapy alone.

Submitted by

Dr Pratyusha Kar
Faculty of Paramedical Sciences