Methylmalonic acidemia

Definition
Methylmalonic acidemia is an inherited metabolic disorder, usually diagnosed in infancy, that causes the accumulation of methylmalonic acid in the body and can lead to severe metabolic disturbances.

Causes, incidence, and risk factors

A defect in the metabolic conversion of methymalonyl-coenzyme A to succinyl-CoA leads to a build up of methylmalonic acid in the body. The disease is usually diagnosed in the first year of life because it can cause seizures and Stroke . Protein in the diet may worsen this condition, so babies who have it may appear normal at birth but show symptoms once they increase their protein intake.

This autosomal recessive disorder (the defective gene must be inherited from both parents) occurs in 1 in 25,000 to 48,000 people. The true rate of occurrence of the disease may be higher, because many neonatal deaths may be caused by undiagnosed metabolic disorders. Both boys and girls are equally affected.

Symptoms

• Vomiting
  
• dehydration
  
• Lethargy
  
• seizures
  
• failure-to-thrive
  
• recurrent infections with Candida sp.
  
• progressive encephalopathy
  
• developmental delays

• serum electrolytes
  
• blood gas for acidosis
  
• serum ammonia levels
  
• serum and urine tests for amino acids and organic acids
  
• serum methylmalonic acid levels
  
• enzyme analysis of fibroblasts for the specific enzyme abnormality
  
• CBC for neutropenia, anemia, and thrombocytopenia
  
• CT scan or MRI of the brain following a seizure

Treatment consists of dietary supplementation with cobalamin, carnitine, and protein restriction.
If cobalamine supplementation doesn’t help, a trial of a diet restricting isoleucine, threonine, methionine, and valine may be useful.

Expectations (prognosis)
Unfortunately, affected patients may not survive their first attack.

Complications

• coma
  
• death

Parents or care-givers of a child with a first seizure should immediately seek medical attention. Infants with failure-to-thrive or developmental delays should see a pediatrician. Adults and children with Stroke s or acute mental status changes should seek immediate medical attention.

Prevention
Following a low-protein maintenance diets and avoiding infection help to reduce recurrent attacks of acidemia. Parents of a child with this disorder or couples desiring children who have a known family history of this disorder should seek information on genetic counseling.

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