Maple Syrup Urine Disease

What is maple syrup urine disease?

Maple syrup urine disease is an inherited disorder in which the body is unable to process certain protein building blocks (amino acids) properly. Beginning in early infancy, this condition is characterised by poor feeding, vomiting, lack of energy (lethargy), seizures, and developmental delay. The urine of affected infants has a distinctive sweet odour, much like burned caramel, that gives the condition its name. Maple syrup urine disease can be life-threatening if untreated.

Maple syrup urine disease can be classified by its pattern of signs and symptoms or by its genetic cause. The most common and most severe form of the disease is the classic type, which appears soon after birth. Variant forms of the disorder appear later in infancy or childhood and are typically milder, but still involve mental and physical retardation if not treated.

How common is maple syrup urine disease?

Maple syrup urine disease affects an estimated 1 in 185,000 infants worldwide. The disorder occurs much more frequently in the Old Order Mennonite population, in which the incidence is about 1 in 358 newborns.

What genes are related to maple syrup urine disease?

Mutations in the BCKDHA, BCKDHB, DBT, and DLD genes cause maple syrup urine disease.

These four genes provide instructions for making proteins that work together as a complex. This complex is essential for breaking down the amino acids leucine, isoleucine, and valine, which are present in many kinds of food (particularly protein-rich foods such as milk, meat, and eggs). Mutations in any of these genes reduce or eliminate the function of the complex, preventing the normal breakdown of leucine, isoleucine, and valine. As a result, these amino acids and their byproducts build up in the body. Because high levels of these substances are toxic to the brain and other organs, their accumulation leads to the serious medical problems associated with maple syrup urine disease.

How do people inherit maple syrup urine disease?

This condition is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder are carriers of one copy of the altered gene but do not show signs and symptoms of the disorder.

What other names do people use for maple syrup urine disease?

• BCKD deficiency
• Branched-chain alpha-keto acid dehydrogenase deficiency
• Branched-Chain Ketoaciduria
• Ketoacidaemia
• MSUD