Maple syrup urine disease

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Maple syrup urine disease
Chemical structure of leucine, one of the branched-chain amino acids involved in the disease
Synonyms	Branched-chain ketoaciduria
Pronounce
Specialty	Medical genetics
Symptoms	Sweet-smelling urine, poor feeding, vomiting, lethargy, developmental delay
Complications	N/A
Onset	Infancy
Duration	Lifelong
Types	Classic, Intermediate, Intermittent, Thiamine-responsive
Causes	Genetic mutation in BCKDHA, BCKDHB, DBT, or DLD genes
Risks	Family history
Diagnosis	Newborn screening, urine test, genetic testing
Differential diagnosis	Phenylketonuria, homocystinuria, organic acidemia
Prevention	None
Treatment	Dietary restriction of branched-chain amino acids, thiamine supplementation
Medication
Prognosis	Variable, depends on type and management
Frequency	1 in 185,000 worldwide; higher in certain populations
Deaths

Maple syrup urine disease (MSUD) is a rare autosomal recessive metabolic disorder affecting branched-chain amino acids. It is named for the distinctive sweet odor of affected infants' urine, which is reminiscent of maple syrup. The condition is caused by a deficiency in the branched-chain alpha-keto acid dehydrogenase complex, leading to the accumulation of the amino acids leucine, isoleucine, and valine in the body.

Signs and Symptoms

The symptoms of MSUD typically appear in the first few days of life. They include poor feeding, vomiting, lethargy, and developmental delay. If untreated, the condition can lead to seizures, coma, and death. The characteristic maple syrup odor in the urine is a key diagnostic feature.

Genetics

MSUD is inherited in an autosomal recessive pattern, meaning that both copies of the gene in each cell have mutations. The parents of an individual with MSUD each carry one copy of the mutated gene but typically do not show signs and symptoms of the condition.

Pathophysiology

The disease is caused by mutations in the genes that encode the branched-chain alpha-keto acid dehydrogenase complex. This complex is responsible for the catabolism of the branched-chain amino acids leucine, isoleucine, and valine. When this complex is deficient or non-functional, these amino acids and their corresponding keto acids accumulate in the blood and urine, leading to the symptoms of MSUD.

Diagnosis

Diagnosis of MSUD is typically made through newborn screening programs that measure the levels of branched-chain amino acids in the blood. Confirmatory testing involves measuring enzyme activity in cultured cells or identifying mutations in the genes associated with the disease.

Treatment

The primary treatment for MSUD is a carefully controlled diet that limits the intake of branched-chain amino acids. This diet must be maintained for life to prevent the accumulation of toxic substances. In some cases, liver transplantation has been used as a treatment, as the liver contains the enzymes necessary to break down the branched-chain amino acids.

Prognosis

With early diagnosis and proper management, individuals with MSUD can lead relatively normal lives. However, they must adhere strictly to dietary restrictions and be monitored regularly for signs of metabolic imbalance.

See also

• Metabolic disorder
• Amino acid
• Autosomal recessive
• Newborn screening
• Liver transplantation

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