What Are the Symptoms of Maple Syrup Urine Disease (MSUD)?

Medically Reviewed on 3/30/2023

Maple syrup urine disease (MSUD) is a rare genetic metabolic disorder that affects the way the body processes branched-chain amino acids (BCCAs), such as leucine, isoleucine, and valine. If left untreated, it can lead to severe neurological damage, coma, and death.

The symptoms of MSUD usually develop within a few days after birth and can vary from mild to severe.

Common symptoms of MSUD

  • Sweet-smelling urine and sweat: Infants with MSUD may have urine that smells sweet and fruity, similar to the smell of maple syrup or burnt sugar. This odor is caused by the buildup of BCAAs.
  • Poor feeding and vomiting: Babies with MSUD may have difficulty feeding, be irritable and fussy, and vomit frequently. This is because high levels of BCAAs can cause nausea, vomiting, and a lack of appetite.
  • Lethargy and poor muscle tone: Infants may appear weak and lethargic, with poor muscle tone and reduced movement.
  • Breathing difficulties: MSUD can affect the respiratory system, leading to rapid breathing, respiratory distress, and apnea (a pause in breathing).
  • Seizures: High levels of BCAAs can affect the central nervous system and cause seizures, which can be life-threatening if left untreated.
  • Behavioral changes: Children with MSUD may experience mood swings, irritability, and restlessness. Moreover, they may have difficulty sleeping and experience night terrors.
  • Developmental delays: If MSUD is not diagnosed and treated early, it can lead to developmental delays, intellectual disability, and other neurological problems.

Early diagnosis and treatment are crucial for infants with MSUD to prevent the development of severe symptoms and long-term complications.

What causes maple syrup urine disease?

Six causes of maple syrup urine disease (MSUD) include the following:

  1. Genetic mutations: MSUD is caused by mutations in one of three genes that provide instructions for making the enzymes responsible for breaking down the branched-chain amino acids (BCAAs). These mutations can be inherited from one or both parents who carry the abnormal gene. Autosomal recessive inheritance is the most common pattern of inheritance for MSUD.
  2. Enzyme deficiency: In individuals with MSUD, the enzymes responsible for breaking down leucine, isoleucine, and valine are deficient or absent. This leads to a buildup of these amino acids and their toxic byproducts, which can cause damage to the brain and other organs.
  3. Dietary triggers: MSUD symptoms can be triggered by consuming foods high in BCAAs, such as dairy products, meat, and certain grains. The accumulation of these amino acids and their byproducts can lead to various symptoms.
  4. Stressful events: Stressful events, such as infections, surgery, or trauma, can also trigger MSUD symptoms by increasing the body's demand for BCAAs. This can lead to a buildup of these amino acids and their byproducts, which can cause neurological symptoms.
  5. Poor compliance with treatment: MSUD requires lifelong management, including strict dietary restrictions and regular monitoring of blood levels of BCAAs. Poor compliance with treatment can lead to a buildup of these amino acids and their byproducts, which can cause symptoms and long-term complications.
  6. Medications and supplements: Some medications and supplements can contain BCAAs, increasing the risk of complications in individuals with MSUD. It is important to carefully review the ingredients of any medication or supplement before taking it.

What age does maple syrup urine disease start?

Maple syrup urine disease (MSUD) is typically diagnosed in infants within the first few days of life as the symptoms can appear shortly after birth. However, in some cases, symptoms may not appear until several days or weeks after birth.

Early diagnosis and treatment are crucial for managing MSUD and preventing serious complications. Therefore, it is important for parents to be aware of the signs and symptoms of the disease and to seek medical attention promptly if they suspect their child may have MSUD.

Can you develop maple syrup urine disease later in life?

Maple syrup urine disease (MSUD) is typically diagnosed in newborns through newborn screening programs as symptoms can develop rapidly within the first few days of life. However, there have been reported cases of individuals developing MSUD later in life.

The onset of symptoms in individuals who develop MSUD later in life can vary widely. Some may experience mild symptoms, such as difficulty concentrating or mood changes, while others may experience more severe symptoms, such as seizures, confusion, and even coma.

There are several possible reasons why someone may develop MSUD later in life. One possibility is that they have a milder form of the disease, which might have been missed during newborn screening. Another possibility is that a genetic mutation predisposes them to the disease later in life. MSUD may also be triggered by increased protein consumption or other stressors that place a greater demand on the body's ability to break down branched-chain amino acids.

How is maple syrup urine disease diagnosed?

The diagnosis of maple syrup urine disease (MSUD) involves a combination of newborn screening, urine and blood tests, genetic testing, molecular testing, and enzyme assays. 

The following are the steps involved in the diagnosis of MSUD:

  • Newborn screening: MSUD can be diagnosed at birth through newborn screening. All babies are screened for a range of genetic disorders shortly after birth, and MSUD is one of them. A small blood sample is taken from the baby's heel and sent to a laboratory for testing.
  • Urine and blood tests: If a newborn screening test indicates a possible diagnosis of MSUD, further tests are needed to confirm the diagnosis. Urine and blood tests are the most common diagnostic tests used for MSUD. In MSUD, the urine smells sweet, like maple syrup. Elevated levels of certain amino acids in the blood also indicate the presence of the disease.
  • Genetic testing: This can confirm the diagnosis of MSUD by detecting mutations in the genes that are responsible for the disorder. This testing is usually done after the diagnosis is confirmed through urine and blood tests.
  • Molecular testing: A type of genetic testing that can identify specific mutations in the genes responsible for MSUD. This type of testing is useful for families with a history of the disease or individuals who have already been diagnosed with MSUD and want to know the specific genetic mutation responsible for their condition.
  • Enzyme assays: Enzyme assays are a type of biochemical test that measures the activity of enzymes in the body. In MSUD, the activity of the enzyme responsible for breaking down the amino acids is reduced or absent. Enzyme assays can help confirm the diagnosis of MSUD.

It is important to diagnose MSUD early to begin treatment promptly and prevent serious complications.

How do you treat maple syrup urine disease?

The treatment of maple syrup urine disease (MSUD) aims to minimize the accumulation of toxic substances in the body and prevent neurological damage. 

Treatment options for MSUD include the following:

  • Dietary management: The most crucial aspect of MSUD treatment is dietary management. Individuals with MSUD need to follow a low-protein diet, which restricts the intake of certain amino acids the body cannot break down. This diet should be closely monitored by a registered dietitian specializing in MSUD management.
  • Branched-chain amino acid (BCAA) supplements: BCAAs are essential amino acids the body cannot synthesize, and individuals with MSUD cannot break them down adequately. Supplementing BCAAs in controlled amounts can help prevent the accumulation of toxic substances in the body.
  • Medical foods: Are specially formulated to meet the nutritional requirements of individuals with MSUD. They are designed to be low in certain amino acids and high in others so the body can break them down easily.
  • Liver transplantation: An option for individuals with severe forms of MSUD that do not respond to other treatments. The liver is the primary organ responsible for breaking down amino acids. A liver transplant can replace the faulty liver with a healthy one, effectively curing MSUD.
  • Gene therapy: A relatively new and experimental treatment option for MSUD. It involves introducing healthy copies of the faulty gene responsible for MSUD into the body, producing a functional enzyme that can break down amino acids correctly.

The treatment of MSUD requires a multidisciplinary approach involving a team of healthcare professionals, including a dietitian, genetic counselor, and specialized physicians. Treatment options may vary depending on the severity of the disease, and a personalized treatment plan is necessary for optimal management of the disease.

Can maple syrup urine disease be cured?

Maple syrup urine disease (MSUD) is a chronic condition, and there is currently no known cure. However, there are treatment options available to manage the symptoms and reduce the risk of complications. Treatment aims to maintain safe levels of amino acids in the blood and prevent their toxic buildup.

The primary treatment for MSUD is a special diet limiting the intake of the three amino acids the body cannot break down. This diet typically involves consuming a special formula containing all the necessary nutrients without the problematic amino acids, along with limited amounts of protein from other sources.

People with MSUD may also need to take supplements of certain vitamins and minerals, such as thiamine, riboflavin, and biotin, necessary for proper metabolic function.

In severe cases of MSUD, additional treatments may be necessary, such as dialysis to remove excess amino acids from the blood or liver transplantation to replace the defective enzyme that causes the condition.

With proper treatment and management, people with the condition can lead relatively normal lives. It is important to work closely with a healthcare provider who is knowledgeable about MSUD to develop an individualized treatment plan and monitor the condition closely.

What foods should you avoid if you have maple syrup urine disease?

Maple syrup urine disease (MSUD) affects the body's ability to break down certain amino acids, including leucine, isoleucine, and valine. If you have MSUD, you need to follow a specialized diet that restricts your intake of these amino acids. 

The types of foods to avoid include the following:

  • Foods high in protein: Because protein is made up of amino acids, you must limit your intake of protein-rich foods, such as meat, poultry, fish, eggs, dairy products, and legumes. These foods contain high levels of amino acids that your body can't break down, so they can cause a buildup of toxins in your blood.
  • High protein supplements: Protein supplements, such as whey protein powder, can also be high in the amino acids you need to avoid. If you need to supplement your diet with additional protein, speak to a registered dietitian who is familiar with MSUD and can recommend appropriate supplements.
  • Certain fruits and vegetables: Some fruits and vegetables, such as avocado, tomato, and spinach, are high in amino acids that you need to avoid. You may need to limit your intake of these foods or choose low-protein alternatives.
  • Baked goods: Many baked goods, such as bread, cake, and cookies, contain high levels of protein-rich ingredients, such as eggs and milk. You should avoid these foods or look for low-protein alternatives.
  • Processed foods: Processed foods, such as deli meats, canned soups, and frozen dinners, often contain added protein and high levels of amino acids you need to avoid. You should read food labels carefully and avoid foods that contain these ingredients.

If you have MSUD, it's important to avoid high-protein foods and supplements, certain fruits and vegetables, baked goods, and processed foods. You should work with a registered dietitian to develop a personalized meal plan that meets your nutritional needs while minimizing your intake of the amino acids that your body can't break down.

What is the life expectancy of someone with maple syrup urine disease?

The life expectancy for someone with maple syrup urine disease (MSUD) depends on the severity of the condition, as well as how well the person can manage their health with a combination of a special diet, medication, and regular monitoring. Generally, people with milder forms of MSUD can have a normal life expectancy. Those with more severe forms may have a shortened life expectancy due to the complications of the condition.

Individuals with classic MSUD, which is the most severe form of the condition, have a higher risk of health complications and a shorter life expectancy compared to those with milder forms of the disease. If left untreated or poorly managed, MSUD can cause severe brain damage, coma, and death. However, with early diagnosis and prompt treatment, many individuals with MSUD can live relatively normal lives.

In recent years, advances in newborn screening and improved treatment options have led to better outcomes for individuals with MSUD. With appropriate management, many people with MSUD can live into adulthood and have a normal lifespan. It is important to note that MSUD is a lifelong condition that requires ongoing management, and individuals with the disease may still be at risk for health complications if their condition is not well-controlled.

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Medically Reviewed on 3/30/2023
Maple Syrup Urine Disease https://rarediseases.org/rare-diseases/maple-syrup-urine-disease/




Overview of maple syrup urine disease https://www.uptodate.com/contents/overview-of-maple-syrup-urine-disease