Maple Syrup Urine Disease (MSUD)

Maple Syrup Urine Disease


Maple syrup urine disease (MSUD) is a rare inherited disorder where the body cannot break down certain parts of protein. The urine of the child smells like a maple syrup.


This disorder occurs in about 1 case per 180,000 newborns.


Maple Syrup Urine Disease is an inherited disorder which follows an autosomal recessive pattern. In this disease the branched-chain alpha-keto acid dehydrogenase complex (BCKDH) responsible for metabolizing some amino acids is absent or deficient.

In some cases, MSUD can damage the brain during infection, fever, fasting or any physical stress experienced by the child. Repeated periods of physical stress result to catabolism of cells releasing amino acids (including leucine, isoleucine and valine) into the bloodstream thereby, leading to mental retardation.


Branched-chain alpha-keto acid dehydrogenase complex (BCKDH) is combination of enzymes that is responsible for the breakdown of the branched chain amino acid. These branched chain amino acids include leucine, isoleucine and valine.

In maple syrup urine disease, the branched chain alpha-keto acid dehydrogenase complex (BCKDH) is absent or deficient resulting to the accumulation of the branched chain amino acids (leucine, isoleucine, and valine) into the urine and blood. Elevated components of leucine, isoleucine and valine that are not metabolized spill out in the urine giving the waste product a distinctive sweet-smelling odor similar to that of maple syrup, hence, the name of the disease. The buildup of the toxic by-products of these amino acids leads to the cerebral degeneration (brain damage) similar to that observed in children diagnosed with Phenylketonuria (PKU) and death, if left untreated.

Clinical Manifestations

Infants with the disorder tend to appear well at birth; however, they quickly show abnormal signs in about 2-7 days depending on the feeding regimen.

  • Feeding difficulty
  • Vomiting
  • Loss of Moro reflex
  • Irregular respirations
  • Opisthotonos
  • Generalized muscular rigidity
  • Generalized seizures
  • Sweet-smelling odor of urine similar to that of maple syrup by the first or second day
  • Poor weight gain
  • Increasing lethargy

If the condition remains untreated, the infant may die as early as 2 to 4 weeks of age.


Prenatal diagnostic tests

  • Amniocentesis
  • Chrorionic villus sampling

Extrauterine diagnostic tests

  • Plasma amino acid test
  • Urine amino acid test


Dietary therapy

  • Low amino acids (leucine, isoleucine and valine) and high thiamine (Vitamin B1) diet is prescribed to the affected infant.

Thiamine, also called Vitamin B1, is responsible for muscle nerve function and a coenzyme for energy metabolism. The child has to comply with the dietary therapy lifelong and must restrict intake of branched chain amino acids without impairing growth and development. This is the main reason why infants are given thiamine.


  • No activity restrictions.

Hemodialysis or peritoneal dialysis

  • This measure can be used to temporarily reduce abnormal serum levels at birth or during a childhood infection, when catabolism of cells releases increased amino acid into the blood stream.


  • Thiamine

Thiamine is a necessary coenzyme in carbohydrate and amino acid metabolism. The oral absorption is poor however, the parenteral route is associated with sever adverse reactions.

Daisy Jane Antipuesto RN MN

Currently a Nursing Local Board Examination Reviewer. Subjects handled are Pediatric, Obstetric and Psychiatric Nursing. Previous work experiences include: Clinical instructor/lecturer, clinical coordinator (Level II), caregiver instructor/lecturer, NC2 examination reviewer and staff/clinic nurse. Areas of specialization: Emergency room, Orthopedic Ward and Delivery Room. Also an IELTS passer.

What Do You Think?