Maple Syrup Urine Disease (MSUD)


Here you’ll find answers to some of the questions that parents often have about this condition. Additional resources are listed at the bottom of the page. Diagnosis and management information can be found in the Maple Syrup Urine Disease (MSUD), which is written for primary care clinicians but also may be of help to parents and family members. Information can also be found in the Maple Syrup Urine Disease Newborn Screening page.

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

Where can I go for further information?

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.


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 (Genetics Home Reference)
Excellent, detailed review of condition for patients and families; sponsored by the U.S. National Library of Medicine.

Newborn Screening Information for Families (NNSGRC)
Information for families about genetic screening. Links to support groups, advocacy groups, and state genetic contacts; National Newborn Screening and Global Resource Center.

Genetics in Primary Care Institute (AAP)
The goal of this site is to increase collaboration in the care of children with known or suspected genetic disorders. It includes health supervision guidelines and other useful resources; represents a collaboration among the Health Resources & Services Administration, the Maternal and Child Health Bureau, and the American Academy of Pediatrics.

Maple Syrup Urine Disease Acute Illness Protocol (NECMP)
Guideline for clinicians treating the sick infant/child who has previously been diagnosed with maple syrup urine disease (MSDU); 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. Click PDF to view the complete protocol.

Emergency Information Form (EIF) for Individuals with Special Health Care Needs (ACEP)
A blank EIF (Emergency Information Form) in Word to download, print, and use in the event of an emergency. Includes diagnoses and procedures; medications; allergies; and signature/consent - from American College of Emergency Physicians.

Patient Education

What is Maple Syrup Urine Disease? (GSLC)
A brief educational overview of single gene disorders that includes the genetics of maple syrup urine disease (MSUD); Genetic Science Learning Center at the University of Utah.


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Authors & Reviewers

Initial Publication: October 2012; Last Update: December 2015
Current Authors and Reviewers (click on name for bio):
Author: Lynne M. Kerr, MD, PhD