Maple syrup urine disease (MSUD), or maple syrup syndrome, is a type of metabolic disorderthat affects the way your body converts food into energy. People with MSUD can’t break down certain amino acids from proteins because their bodies don’t produce the necessary enzymes. This causes a buildup of toxins in your body that can damage your brain and other organs. It can even lead to death if untreated.
Here is what you need to know about MSUD.
What Causes Maple Syrup Urine Disease?
Maple syrup syndrome is a very rare genetic disorder, with only about 1 in 185,000 infants born with the condition.
MSUD is caused by mutations or changes in some of your genes. Those changes prevent your body from making enzymes that break down three amino acids in proteins—leucine, isoleucine, and valine. MSUD is recessive, so you must have inherited two copies of the mutated genes to have symptoms.
If you and your partner carry the mutated genes that cause MSUD, there is a 25% chance that your baby will have the disease. There is a 50% chance that your baby will become a carrier themselves, and a 25% chance that they will not inherit the mutated genes at all.
Types of Maple Syrup Urine Disease
There are four main types of MSUD:
Classic—or infantile—MSUD. The most common and severe form of the disease, babies born with classic maple syrup syndrome will usually show symptoms in the first three days after birth. Babies born with classic MSUD either completely lack the necessary enzymes or produce too few of them to effectively break down amino acids.
Intermediate MSUD. People with this form of MSUD make more enzymes and can break down the amino acids better than people with classic MSUD. Symptoms will usually be less severe than classic MSUD and show up in babies and children between ages 5 months and 7 years.
Intermittent MSUD. Children with this type of maple syrup syndrome will grow and develop normally. If you have intermittent MSUD, symptoms usually won’t show up until sickness or stress causes them to appear. Compared to people with classic MSUD, those with this type of maple syrup syndrome can often tolerate higher levels of the amino acids in their urine and bloodstreams.
Thiamine-responsive MSUD.Thiamine, or vitamin B1, helps boost enzyme activity so that your body can break down amino acids better. The vitamin alone is not enough to remove symptoms entirely. People with this type of MSUD typically will see improvement of their symptoms when taking high doses of thiamine and following a special diet that limits protein.
What Are the Symptoms of Maple Syrup Urine Disease?
The most distinct and easily recognizable symptom of MSUD is the smell. Urine, sweat, and even the earwax of people with MSUD will often have a sweet smell similar to maple syrup or burnt sugar.
The severity and number of symptoms varies for each person with the disease and each type of MSUD.
Babies with untreated classic MSUD might be more irritable, have longer or irregular sleep patterns, and have difficulty eating and breathing. They might also have muscle spasms, fall into a coma, or stop breathing entirely. As they get older, they are at risk for physical and mental disabilities or developmental delays.
Intermediate, intermittent, and thiamine-responsive MSUD symptoms can happen at any age. Sometimes, MSUD symptoms can show up or become worse if you are sick or under stress. Symptoms in older children or adults include:
- Stomach pain
- Vomiting
- Anorexia and weight loss
- Muscle weakness or loss of control
- Involuntary movements
- Slurred speech
- Changes in consciousness or trouble remaining alert
How Is Maple Syrup Urine Disease Diagnosed?
Newborn screening tests in the U.S. include MSUD, so classic MSUD is often diagnosed shortly after birth. Doctors can confirm the diagnosis with further blood and urine tests.
Doctors can diagnose other types of MSUD by checking for the telltale maple syrup smell, comparing other symptoms, and performing blood, urine, or genetic testing.
What Is the Treatment for Maple Syrup Urine Disease?
Maple syrup syndrome is treated by controlling the buildup of amino acids in your body. If you have MSUD, your doctor will have you follow a special diet to restrict the amount of protein you eat while still providing the nutrients your body needs.
If you have severe symptoms, your doctor might use other medical treatments such as IVs or feeding tubes to help deliver needed nutrients. Doctors might also use glucose or insulin IVs to help regulate the amount of amino acids in your blood, or filter your blood completely with a type of dialysis.
Liver transplants offer a permanent treatment for MSUD. Donated livers will produce the necessary enzymes to break down the amino acids and allow people with MSUD to live without any symptoms or restrictive diets.