What Is Maple Syrup Urine Disease (MSUD)?

Maple syrup urine disease (MSUD) is an inherited condition caused by a faulty gene. It typically starts in early infancy.

In children with MSUD, the body can't break down certain amino acids. Amino acids are the pieces that build proteins.

The disease gets its name from the distinctive sweet smell of the urine of children who have it.

How Common Is MSUD in Kids?

Worldwide, MSUD is rare. It affects about 1 in 185,000 infants.

But it's more common in certain populations.

In the Old Order Mennonite community, it affects about 1 in 380 newborns. Among Ashkenazi Jewish populations, it affects about 1 in 26,000 infants.

What Causes MSUD in Children?

Families pass down the genes that cause maple syrup urine disease.

Specifically, changes in any of these three genes causes MSUD:

These genes make proteins called enzymes that break down certain amino acids or other molecules in the blood.

If the body can't break these down, they build up in the blood and can become toxic. This makes children sick.

For a baby to be born with MSUD, each parent must carry a copy of the same mutated gene. Parents with only one broken gene often don't know because they don't have any symptoms.

Maple Syrup Urine Disease Symptoms

Babies with MSUD can start to have problems a few days after they’re born. In just a few days, amino acids and their toxic byproducts build up in the blood and urine.

This causes symptoms such as:

  • Pee or earwax that smells like maple syrup.
  • Lethargy and ill temper.
  • Feeding problems and poor appetite.
  • Seizures or abnormal movements.
  • Vomiting.

There are different types of MSUD.

The intermediate form of MSUD is less severe. Symptoms may not start until a baby is a few months old.

A baby with the most severe form of MSUD may not survive more than a few weeks without treatment.

With intermittent MSUD, a child may only have symptoms some of the time. They may flare up when the child is sick or under stress.

How Do You Diagnose MSUD in Children?

All states in the U.S. screen newborns for MSUD at birth, using blood taken from a heel prick.

This helps doctors catch the most severe form of MSUD right away so they can start treatment before symptoms start.

The milder or intermittent forms of MSUD may not appear in the newborn heel prick test.

In this case, if your child's doctor suspects MSUD, they'll run:

  • Blood tests to see the amino acid level in a baby's blood.
  • Urine tests to see the level of amino acids in their pee.
  • Genetic testing of the blood to see which gene mutation is causing MSUD.

Maple Syrup Urine Disease Treatment

A newborn with MSUD will need a special formula. It has low levels of the three amino acids the body can't break down.

As children with MSUD grow, they must be on a special low-protein diet. Parents work directly with a nutritionist or specialist in child development.

Children with MSUD may also need:

UPMC Children's also offers liver transplants for children with the most severe MSUD.

The liver makes enzymes that break down amino acids, so for many children, a new liver can cure MSUD. Post-transplant, they have normal liver function and can eat whatever they want.

George Mazariegos, MD

Chief of Pediatric Transplant

Dr. Mazariegos and his team developed the liver transplant protocol for MSUD.

Your Child's MSUD Consult and Care: What to Expect

If your child has maple syrup urine disease, we want you to know that you're not alone. The Center for Rare Disease Therapy (CRDT) at UPMC Children's Hospital of Pittsburgh is here to help.

To make an appointment for your child or refer a patient for MSUD care:

In most cases, a genetic disease expert can see your child within 1 to 2 weeks.

Here's what you can expect when you come to us for a consult.

What should I expect at my child's first visit for MSUD?

Your first visit to the CRDT will take from 4 to 6 hours.

The doctor will give your child a complete assessment. They'll confirm your child's MSUD diagnosis and learn how much it affects your child.

Since we work as a team, your child may see many other rare disease center doctors and staff such as:

  • Brain, spine, and nervous system experts.
  • Heart doctors.
  • Surgeons.
  • Nutritionists.
  • Genetic counselors.
  • Psychologists.
  • Child development specialists.

You'll have a care plan tailored to your child's needs by the end of your visit. You'll also have a follow-up visit in three months.

You'll meet our clinical nurse practitioner who can help you with any concerns between now and your next appointment.

How long will I need to wait for my child's MSUD test results?

It depends on the types of tests the doctor ordered. But, in most cases, you can expect a phone call within 2 weeks.

We'll explain the test results and discuss next steps for your child's MSUD care.

You can also find your child's test results if you signed up for the MyCHP patient portal.

MyCHP lets you manage your child's health online. It's free for patients, parents, and guardians of UPMC Children's Hospital of Pittsburgh.

Learn more about Leah's experience with Maple Syrup Urine Disease at Children's Hospital.Leah's Story: Liver Transplant Cures Her MSUD

A liver transplant cured Leah's maple syrup urine disease. Doctors at the Hillman Center for Pediatric Transplantation at Children's lead the world in performing this procedure.

Learn More »

Contact Us About Your Child’s MSUD

At the CRDT, every child diagnosed with a rare disease receives a tailored treatment plan and family-centered care.

For an appointment, consult, or referral, contact us:

We’ll be in touch within 2 business days.