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Methylmalonic acidemia with homocystinuria

(meth-uhl-muh-LAHN-ik • a-suh-DEE-mee-uh • with • HOH-moh-SIS-tin-UR-ee-uh)

General Condition Information

Other Names

  • Cobalamin C deficiency
  • Cobalamin C,D cofactor deficiency
  • Disorders of intracellular cobalamin metabolism (cblC, D, E, F, G, J, X)
  • Methylmalonic acidemia
  • Methylmalonic acidemia (Cbl C, D)
  • Methylmalonic acidemia with homocystinuria (Cbl C, D)
  • Methylmalonic acidemia with homocystinuria- Cobalamin C, D disorders
  • Methylmalonic acidemia- Other
  • Methylmalonic acidemia: Cbl C & D
  • Methylmalonic acidemia: cobalamin C, D

Condition Type

Birth Prevalence

  • It is estimated that fewer than 70 babies are born with this condition each year in the United States. 
  • Visit GeneReviews to learn more about how often this condition occurs.

Screening Finding

Increased C3 acylcarnitine +/- increased homocysteine

What is Methylmalonic acidemia with homocystinuria

There are different forms of methylmalonic acidemia, each with different causes and treatments. Methylmalonic acidemias are inherited (genetic) conditions that prevent the body from breaking down certain proteins, cholesterol, and fats. Homocystinurias occur when urine releases part of a protein called homocysteine. Methylmalonic acidemia with homocystinuria is a combination of both of these conditions.

Methylmalonic acidemias develop when enzymes that use vitamin B-12 to help digest certain proteins, fats, and cholesterol do not work properly. Homocystinuria results because an enzyme that needs vitamin B-12 cannot turn homocysteine into methionine, an important building block of proteins.

If your baby cannot break down proteins, fats, and cholesterol, toxins can build up. When these toxins are acids, blood can become acidic (acidemia). Also, the buildup of homocysteine can increase the likelihood of blood clots and can cause other damage. Acidemia and increased homocysteine can lead to the signs and symptoms of the condition.

Newborn Screening and Follow-Up

Condition Details

Treatment and Management

It is important to talk to your health care provider about which treatment(s) are best for your baby. The goal of treatment is to prevent the health problems caused by this condition.

Treatments may include the following:

  • Vitamin B-12 treatments
  • L-carnitine supplements
  • Betaine supplements
  • Low-protein diet
  • Special formulas
  • Frequent feedings to avoid long periods without food

Children who receive early and ongoing treatment for methylmalonic acidemia with homocystinuria can have healthy growth and development.

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