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Maple syrup urine disease- An Overview

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Maple syrup urine disease is a genetic condition due to an enzyme defect in the branched-chain amino acid leucine, isoleucine, and valine pathway. Read to know more.

Medically reviewed by

Dr. Prakashkumar P Bhatt

Published At December 29, 2022
Reviewed AtJune 26, 2023


Maple syrup urine disease is a rare genetic disease caused by a defect in the branched chain alpha ketoacid dehydrogenase complex and is a life-threatening metabolic disease. The condition can lead to coma (period of prolonged unconsciousness due to any injury or illness), seizures (abnormal electrical activity in the brain), and death if left untreated. Its pattern of symptoms and signs often classifies it.

What Is Maple Syrup Urine Disease?

Maple syrup urine disease is a rare inherited disease in which the human system cannot process protein building blocks properly. It is also known as branched-chain ketoacid dehydrogenase deficiency (BCKD) and branched-chain ketoaciduria.

What Causes Maple Syrup Urine Disease?

Amino acid helps children in growth and development. They are used to make proteins by body mechanisms. In maple syrup urine disease, three amino acids, isoleucine, valine, and leucine, are not broken down. All the amino acids and their corresponding byproducts buildup in the blood can potentially damage the brain and other organs. It is inherited as an autosomal recessive pattern, meaning parents carry the mutated gene to the child with maple syrup urine disease. When two carrier parents plan a child together, they usually have a 25 % chance of having a child with a corresponding disease during pregnancy.

What Are the Different Types of Maple Syrup Urine Disease?

There are four types of maple syrup urine disease such as :

  • Classic: Classic maple syrup urine disease is one of the most common and severe types of maple syrup urine disease. Symptoms are seen within the first three days of the birth.

  • Intermediate: It is less severe than classic maple syrup disease, in which the symptoms appear in children between 5 months and seven years.

  • Intermittent: It develops in children due to infection or a period of stress leading to maple syrup urine disease.

  • Thiamine-Responsive: It responds to treatment with high doses of vitamin B1 and a restricted diet.

How Common Is Maple Syrup Urine Disease?

Maple syrup urine disease is usually a rare disease that occurs 1 in every 185,000 births worldwide. It is mostly seen in a population with a small pool or when close relatives and cousins have children together. Males and females are equally affected.

Who Is Mostly Affected by Maple Syrup Urine Disease?

Maple syrup urine disease affects people whose parents are in close relation and are much more likely to have metabolic disease. It frequently occurs among Mennonites in the United States, where members of the same community marry each other.

What Are the Symptoms Associated With Maple Syrup Urine Disease?

Maple syrup urine disease symptoms are usually seen in newborns 48 hours after birth. In older children, signs of intermittent, intermediate, and thiamine-responsive maple syrup urine disease develop before seven years. The symptoms of maple syrup urine disease are as follows :

  • Urine, earwax, and sweat smell like burnt sugar or maple syrup.

  • Vomiting, loss of appetite, irritability, and poor feeding.

  • Tiredness and weakness.

  • Changes in muscle tone, such as muscle tightness or poor muscle tone.

  • Developmental delay.

  • Abnormal muscle movements are a spasm that causes backward arching of the neck, spine, and head.

  • Convulsion (uncontrolled shaking, rapid and rhythmic shaking with muscle relaxation and contraction repeatedly).

  • Irregular sleep activity.

  • High-pitched cry.

  • Neurological deficiencies.

How Is Maple Syrup Urine Disease Diagnosed?

Maple syrup urine disease can be diagnosed by the following tests such as :

  • Maple Syrup Smell: A distinguished smell of maple syrup in the sweat and urine of the patient.

  • Plasma Amino Acid Test: It is performed to access elevated levels of branched-chain amino acid and to detect I- alloisoleucine.

  • Genetic Test: It is done to identify any mutation of branched-chain ketoacid dehydrogenase genes.

  • Blood and Urine Disease: Finger stick tests are performed and sent to a laboratory to determine blood levels of valine, leucine, and isoleucine.

What Are the Complications Seen in Child With Maple Syrup Urine Disease?

People with maple syrup urine disease develop a complication that varies from mild to severe. The complication of maple syrup urine disease includes:

  • Increased risk of depression and anxiety.

  • Loss of bone mass that causes the bone to fracture easily.

  • Swelling of the pancreas during crisis states.

  • Movement disorders such as uncontrolled muscle contractions and tremors.

  • Coma and death arise from infection, poor dietary control, or stress.

  • Blindness.

  • Swelling of the brain.

  • Severe neurological damage.

  • Loss of alertness.

  • Osteoporosis (a condition where bones become brittle and weak).

  • Acute pancreatitis (a situation where the pancreas becomes swollen over a short period).

  • Cerebrovascular ischemia (acute brain injury that results from impaired blood flow to the brain).

How to Prevent Maple Syrup Urine Disease?

There is no method of preventing maple syrup urine disease as it is inherited. However, genetic testing is helpful to know whether the partner is a carrier of the disease or not. In addition, genetic testing can identify the fetus's condition before birth.

How to Treat Maple Syrup Urine Disease?

  • Early diagnosis and initiation of therapy are the keys to successful treatment.

  • Maple syrup urine disease is usually treated by controlling the buildup of amino acids in the body and lifelong monitoring of leucine, isoleucine, and valine amino acid levels in the blood.

  • Protein restricted diet promotes proper development and growth to prevent amino acid buildup. Therefore, a diet rich in branched-chain amino acids is indicated, as it stimulates the building of muscle proteins and possibly reduces muscle breakdown.

  • Liver transplantation is considered a reliable treatment option. This renders the patient symptom-free and enables them to eat normal food again.

  • Elimination of toxic metabolites.

  • Thiamine (Vitamin B1) in doses of 10 mg to 1000 mg daily improves leucine tolerance in some patients. However, dietary restriction is still necessary.

  • Pyridoxine therapy can be tried for all, as it increases the cystathionine β-synthase (CBS) activity. A methionine-restricted and cystine-supplemented diet are recommended for all who respond well to Pyridoxine.

  • Hemofiltration or dialysis is sometimes done to lower the level of the three amino acids in the blood.

  • Intravenous (I.V) glucose and insulin are sometimes given to the patient to adjust the levels of amino acids.


Maple syrup urine disease has a variable presentation and clinical course. When a metabolic attack occurs, patients must seek medical attention immediately. The risk of brain damage and other complications can be reduced with immediate care. New treatment modalities are needed to manage difficult cases better. Early detection and intervention remain the key to a practical treatment approach in classical and non-classical cases.

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Dr. Prakashkumar P Bhatt
Dr. Prakashkumar P Bhatt



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