Maple Syrup Urine Disease (MSUD) (FAQ)

Answers to questions families often have about caring for their child with maple syrup urine disease

What is maple syrup urine disease (MSUD) and what causes it?

MSUD is a genetic metabolic condition caused by an accumulation of the branched-chain amino acids (BCAAs) leucine, isoleucine, and valine, and related ketoacids.

What are the symptoms of MSUD?

Accumulation of these compounds (especially leucine) disturbs brain cell volume regulation and results in brain edema and secondary impairment of neuron growth, myelin synthesis, and cerebral neurotransmitter production leading to physical and intellectual disability and, if untreated, death.
In addition to the classic form, there are variant forms of the disease – intermediate, intermittent, and thiamine responsive–which may have milder and later onset of symptoms, presenting with anorexia, poor growth, irritability, seizures, or developmental delay in late infancy or childhood. Symptoms and metabolic crisis episodes may be precipitated by illnesses or excess protein intake.

How it is diagnosed?

Diagnosis is made by urine and blood testing. MSUD is usually diagnosed by newborn screening.

What is the prognosis?

With treatment before any crises occur, lifetime adherence to the diet, and prompt treatment of illnesses, prognosis is good, and normal development and IQ are expected. Females with MSUD are capable of having normal children, but need to adhere strictly to the diet and be monitored carefully, particularly postpartum, by metabolic geneticists. Without treatment, one can expect intellectual disability, neurologic disturbances, and early death.

What is the risk for other family members or future babies?

MSUD is an autosomal recessive disorder. Mutations in three genes cause MSUD—BCKDHA, MCKDHB, and DBT—and can be tested for on a clinical basis.

What treatments/therapies/medications are recommended or available?

Treatment for MSUD consists of a diet low in branched chain amino acids with, in most cases, supplements of isoleucine and valine. Some patients respond to high doses of thiamine with increased protein tolerance. Infants and children with MSUD require close monitoring by their primary care clinician and their metabolic geneticist and nutritionist. Medical treatment is similar in the different types of MSUD, with milder forms requiring less protein restriction. Treatment needs to be continued for life for classic MSUD and all variant forms.

How will my child and our family be impacted?

With strict adherence to the diet, your child should do well. He or she will, however, need metabolic monitoring and will have to follow a strict diet and possibly take medication (thiamine). This will make things more difficult for your family and your child. Your metabolic geneticists will help you learn how to follow a diet necessary for the best outcome. A support group may be helpful (see below).

If MSUD is a genetic disease, then why is no one else in my family or extended family affected?

MSUD is an autosomal recessive condition. That means that a child needs to have 2 MSUD genes to be affected, 1 from the mother and 1 from the father, who are themselves unaffected. It is possible that other extended family members also carry an MSUD gene, but have not had a child with another person also carrying the MSUD gene.

Why does the urine smell like maple syrup?

The substance responsible for the odor in urine (and cerumen or ear wax) in individuals with MSUD is also found in maple syrup and fenugreek.

Can I breast-feed my baby with MSUD?

On diagnosis, all breastfeeding is stopped to avoid a metabolic decompensation while blood testing is performed and a diet initiated. Breastfeeding can sometimes be resumed after the diet has been instituted, although with controls to limit the intake of branched chain amino acids normally present in breast milk. Dietary changes in the mother do not modify significantly the content of branched chain amino acids in breast milk.

Will my female child with MSUD be able to have children?

Most women with MSUD are able to become pregnant and have healthy babies assuming they are strictly adherent to the diet and are monitored carefully through pregnancy and postpartum. The latter is actually more of a risky time for the mother because of all the changes going on in the woman's body post-pregnancy and metabolic monitoring will need to continue for several months after birth. Maple Syrup Urine Disease (GeneReviews)


Information & Support

Related Portal Content
Maple Syrup Urine Disease (MSUD)
Assessment and management information for the primary care clinician caring for the child with maple syrup urine disease (MSUD)

Care Notebook
Medical information in one place with fillable templates to help both families and providers. Choose only the pages needed to keep track of the current health care summary, care team, care plan, health coverage, expenses, scheduling, and legal documents. Available in English and Spanish.

For Parents and Patients


Maple Syrup Urine Disease Family Support Group
A non-profit organization that provides information, newsletters and articles, family stories, support services, recipes and formulas, and dietary resources.


Emergency Information Form (EIF) for Individuals with Special Health Care Needs (PDF Document 61 KB)
A blank Emergency Information Form PDF to download, print, and use in the event of an emergency. Includes diagnoses and procedures; medications; allergies; and immunizations; American College of Emergency Physicians and American Academy of Pediatricians.

Maple Syrup Urine Disease - Information for Parents (STAR-G)
A fact sheet, written by a genetic counselor and reviewed by metabolic and genetic specialists, for families who have received an initial diagnosis of a newborn disorder; Screening, Technology and Research in Genetics.

Maple Syrup Urine Disease (NECMP)
Guideline for clinicians treating the sick infant/child who has previously been diagnosed with maple syrup urine disease (MSUD); developed under the direction of Dr. Harvey Levy, Senior Associate in Medicine/Genetics at Children’s Hospital Boston, and Professor of Pediatrics at Harvard Medical School, for the New England Consortium of Metabolic Programs.

Services for Patients & Families in Nevada (NV)

For services not listed above, browse our Services categories or search our database.

* number of provider listings may vary by how states categorize services, whether providers are listed by organization or individual, how services are organized in the state, and other factors; Nationwide (NW) providers are generally limited to web-based services, provider locator services, and organizations that serve children from across the nation.

Authors & Reviewers

Initial publication: October 2012; last update/revision: December 2015
Current Authors and Reviewers:
Author: Lynne M. Kerr, MD, PhD