Methylmalonic acidemia

Definition

Methylmalonic acidemia is a disorder, passed down through families, in which the body cannot break down certain proteins and fats. The result is a build up of a substance called methylmalonic acid in the blood.

It is considered an inborn error of metabolism.

Causes, incidence, and risk factors

The disease is usually diagnosed in the first year of life. It is an autosomal recessive disorder, which means the defective gene must be passed onto the child from both parents.

About 1 in 25,000 - 48,000 babies are born with this condition. However, the actual rate may be higher, because a newborn may die before the condition is ever diagnosed. Methylmalonic acidemia affects boys and girls equally.

Symptoms

The disease can cause seizures and stroke. Babies may appear normal at birth, but develop symptoms once they start eating more protein, which can cause the condition to get worse.

Symptoms include:

• Brain disease that gets worse (progressive encephalopathy)
• Dehydration
• Developmental delays
• Failure to thrive
• Lethargy
• Repeated yeast infections
• Seizures
• Vomiting

Signs and tests

Testing for methylmalonic acidemia is often done as part of a newborn screening exam. The U.S. Department of Health and Human Services recommends screening for this condition at birth because early detection and treatment has been shown to be beneficial.

Tests that may be done to diagnose this condition include:

• Ammonia test
• Blood gases
• Complete blood count
• CT scan or MRI of the brain
• Electrolyte levels
• Genetic testing
• Methylmalonic acid blood test
• Plasma amino acid test

Treatment

Treatment consists of cobalamin and carnitine supplements and a low-protein diet. The child's diet must be carefully controlled.

If supplements do not help, the doctor may also recommend a diet that avoids substances called isoleucine, threonine, methionine, and valine.

Liver or kidney tranplantation (or both) have been shown to help some patients. These transplants provide the body with new cells that help breakdown methylmalonic acid normally.

Expectations (prognosis)

Patient may not survive their first attack.

Complications

• Coma
• Death
• Kidney failure

Calling your health care provider

Seek immediate medical help if a child is having a seizure for the first time. See a pediatrician if your child has signs of failure-to-thrive or developmental delays.

Prevention

A low-protein maintenance diet can help to reduce the number of acidemia attacks. Persons with this condition should avoid those who are sick.

Genetic counseling may be helpful for couples with a family history of this disorder who wish to have a baby.

References

Rezvani I. Defects in metabolism of amino acids. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 85.