Maple Syrup Urine Disease: Symptoms & Prevention

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While the name of Maple Syrup Urine Disease (MSUD) may sound sweet, it can be a very serious health condition, so understanding the symptoms, causes, and potential treatments are very important.

What is Maple Syrup Urine Disease (MSUD)?

This unusually named disease is an autosomal recessive metabolic disorder that is hereditary, occurring when an infant receives a mutated gene from each parent. The name – maple syrup urine disease – comes from the peculiar smell of a person’s urine suffering from this metabolic disorder. The urine often smells sweet or saccharine, like maple syrup; the earwax of affected individuals may also smell like a sweet syrup.

The disease itself prevents the body from breaking down certain amino acids – leucine, isoleucine, and valine – that are necessary for development and natural functions. Since the body can’t break these chemicals down, they begin to build up in the blood, where they continue to release their byproducts, keto acids. In the worst cases, having this condition can result in brain damage, in addition to various other unpleasant side effects. Maple syrup urine disease goes by a number of other names, including the following:

  • BCKDC deficiency
  • Branched-chain alpha-keto acid dehydrogenase deficiency
  • Branched-chain ketoaciduria
  • Branched-chain ketonuria I

Types of MSUD

There are a number of variations within MSUD, including Classic, Intermediate, Intermittent, and Thiamine-responsive types.

Classic MSUD

In this form, there is very little enzymatic activity to break down certain amino acids – less than 2% of the normal activity level.

Intermediate MSUD

The enzyme levels are higher in this form – roughly 3-10% of normal activity. This is a rare variety and can present at any time of life.

Intermittent MSUD

Usually not appearing until between ages 1 and 2, this is a milder form of MSUD, with enzyme activity often reaching 15%.

Thiamine-Responsive MSUD

This form of MSUD is responsive to high levels of thiamine, which can counter the side effects and risks of this disease.

Symptoms of Maple Syrup Urine Disease

There are a number of symptoms that may indicate you or your child is suffering from this disease, including seizures, fatigue, vomiting, and difficulty eating, among others. In the case of infants diagnosed with this disease, they may appear completely normal at birth, but the rapid buildup of amino acids can cause potentially permanent brain damage. In very severe cases of the disease, infants often die within the first six months. Some of the other symptoms of this condition are listed below.

  • Feeding difficulties
  • Lethargy
  • Seizures
  • Urine that smells like maple syrup
  • Vomiting
  • Weight loss
  • Earwax that smells of maple syrup
  • Poor growth
  • Learning and developmental disabilities
  • Irregular sleep patterns
  • Coma
  • Constant crying
  • Brain damage

Causes of Maple Syrup Urine Disease

Extensive research has identified the primary cause of MSUD, which is a genetic mutation. This disease can be passed through families, as it is an autosomal recessive genetic disorder. The reason this condition is so rare is that an infant needs to receive both recessive genes from each parent to develop the condition. While there may be other minor genetic factors that can regulate the severity of the condition, as well as the age at which it manifests, there is no indication of any environmental causes. Periods of intense physical stress can cause the condition to emerge for the first time, or flare up in those who suffer from the disease.


In many countries, a blood test is administered at birth to screen for a number of diseases, and maple syrup urine disease is one of them. Genetic testing is also available for both parents to determine whether they are both carriers of the recessive gene. If you are in a country that doesn’t have a comprehensive blood panel at birth, a urine analysis test or a plasma amino acid test can be administered later in life, which will measure the levels of amino acids in your blood plasma or urine.

If an infant is diagnosed with this condition, it will require aggressive treatment and management to prevent birth defects or even infant death. As an older individual, being diagnosed will mean choosing a treatment strategy to keep the condition under control and try to maintain a normal quality of life.

Treatments for Maple Syrup Urine Disease

The most effective treatments for maple syrup urine disease include changing your diet, going on dialysis, or amino acid supplementation, among others.

Dietary Changes

While protein is an essential part of our diet, it is also the source of the amino acids that cannot be digested by the body. Cutting back on protein intake, or specializing which amino acids you are consuming, can be an effective treatment for this condition.


Dialysis is an unpleasant and time-consuming treatment method, but it can clean your blood and eliminate excess amino acids and keto acids from the body.

Amino Acid Supplementation

Often in conjunction with a protein-free diet, amino acid supplementation can be administered intravenously, but without BCAAs (branched-chain amino acids), so there is no risk of buildup in the blood.

Possible Complications

If this condition is left untreated, and the body experiences a metabolic crisis – a period of intense stress on the body – it can cause some very unpleasant side effects and complications. These include extreme fatigue, loss of cognitive function, irritability, vomiting, seizures, swelling of the brain, lack of blood to the brain, and even a coma. It is possible to never be diagnosed with this condition, as the symptoms never appeared when you were younger. However, if a metabolic crisis occurs and this disease finally reveals itself, it can be very dangerous. The most severe complications include permanent neurological damage, blindness, intellectual disabilities, and even death, in some cases.

Prevention of Maple Syrup Urine Disease

Preventing a genetic-linked disease is difficult, if not impossible, but being aware that you are at risk, and thus avoiding certain factors that can increase your chances of experiencing a flare-up, is a good preventative measure.

Family History: If you are familiar with your family’s medical history, it will let you know if you are at risk of having this disease, or of potentially passing it on to your children.

Early Testing: Getting tested in your newborn period is the best way to inform yourself and take the necessary action should the test come back positive. If not done at birth, plasma or urine testing should be done early on.

Dietary Alterations: Certain foods can exacerbate the condition, or make you more likely to have an episode or a metabolic crisis. Protein, in particular, should be reduced from your diet, as this is where many of the excess amino acids will be coming from.

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