Maple Syrup Urine Disease (MSUD)

Maple Syrup Urine Disease (MSUD)



Maple Syrup Urine Disease (MSUD) is an autosomal recessive metabolic disorder. MSUD is a rare disorder that occurs in about 1 out of every 185,000 births worldwide.[1] The baby receives two copies of the altered genes – one from the mother and one from father in which the body is unable to breakdown amino acids – Leucine, Isoleucine and Valine.[2] This results in a buildup of harmful substances in the blood and urine. One of the main characteristics of this disorder is sweet-smelling urine, hence the name, MSUD.[3] This disorder is also known as BCKDC deficiency, branched-chain alpha-keto acid dehydrogenase deficiency.


Maple syrup urine disease (MSUD) is categorized as classic (severe), intermediate, intermittent and thiamine responsive.

CLASSIC: This is the most common and severe form of this disorder and generally present in new-borns.  The symptoms such as poor feeding, increased lethargy and irritability are present within a few days of birth. The onset is usually triggered when the infant’s body begins to process protein from feedings.[4]

INTERMEDIATE: This is a rare type of MSUD.  The symptoms are similar to classic MSUD but the age of onset varies greatly. This disorder is diagnosed between 5 months & 7 years. Children with this type of MSUD have a higher level of enzyme activity than classic MSUD.[4]

INTERMITTENT:  The symptoms usually do not appear until a child is between 1 and 2 years of age. It’s a milder form of classic MSUD and children can tolerate normal protein levels in the diet. The children with intermittent MSUD have significant enzyme activity — about 8 to 15 percent higher than normal activity. The initial onset happens when the child experiences stress, illness, or an unusual increase in protein.[4]

THIAMINE RESPONSIVE: This rare form of the condition is responsive to large doses of thiamine, or vitamin B-1 which improves enzyme activity. Symptoms usually occur after infancy.[4]


Every baby is screened to detect 1 of 9 rare conditions and to avoid any serious complications. The newborn blood spot screening is also known as the heel prick test.[3] The symptoms of this disorder are sweet-smelling urine/sweat with maple syrup odor, weight loss, loss of appetite, breathing difficulties, lethargy, vomiting, irritability, shrill cry, seizures, loss of consciousness, irregular respiration, apnea, ear wax, etc. [3]


Children diagnosed with MSUD are given a low protein diet to reduce the amount of amino acids.  Some children may need to take supplements of isoleucine and valine.


In 1997, liver transplantation was reported in a child with MSUD who had developed acute liver failure. The liver transplant was successful and the previously diagnosed MSUD was metabolically cured. The MSUD transplant protocol has been adopted with high success rates with normalisation of amino acid profiles within a few hours after transplant and continuing to remain so despite advancing to a regular diet of unrestricted protein.[5]



  1. Maple Syrup Urine Disease (MSUD) | Cleveland Clinic. (2019). Cleveland Clinic.
  2. Strauss, K. A., Puffenberger, E. G., & D Holmes Morton. (2013, May 9). Maple Syrup Urine Disease.; University of Washington, Seattle.
  3. Maple syrup urine disease. (2017, October 19).
  4. Giorgi, A. (2016, October 11). Maple Syrup Urine Disease (MSUD). Healthline; Healthline Media.
  5. George V., M. (2019). Pediatric Maple Syrup Urine Disease | Children’s Pittsburgh. Children’s Hospital of Pittsburgh.


Meghna Ravi
Pristine Organics