methylmalonic aciduria (cobalamin deficiency) cblB type
The MMAB gene provides instructions for making an enzyme that is involved in the formation of a compound called adenosylcobalamin (AdoCbl). AdoCbl, which is derived from vitamin B12 (also known as cobalamin), is necessary for the normal function of another enzyme known as methylmalonyl CoA mutase. This enzyme helps break down certain proteins, fats (lipids), and cholesterol.
The MMAB enzyme is active in mitochondria, which are specialized structures inside cells that serve as energy-producing centers. Once vitamin B12 has been transported into mitochondria, the MMAB enzyme converts a form of the vitamin called cob(I)alamin to AdoCbl. Studies suggest that this enzyme may also deliver AdoCbl to methylmalonyl CoA mutase.
At least 25 mutations in the MMAB gene have been found to cause methylmalonic acidemia, a condition characterized by feeding difficulties, developmental delay, and long-term health problems. Some of these genetic changes delete or duplicate a small amount of genetic material in the MMAB gene. Other mutations change a single protein building block (amino acid) used to make the MMAB enzyme. Researchers believe that nearly all of these mutations lead to the production of a nonfunctional version of the enzyme. As a result, AdoCbl cannot be made properly. A lack of AdoCbl impairs the function of methylmalonyl CoA mutase, which results in the incomplete breakdown of certain proteins and lipids. This defect allows toxic compounds to build up in the body's organs and tissues, causing the signs and symptoms of methylmalonic acidemia.
- ATP:Cob(I)alamin Adenosyltransferase
- cob(I)alamin adenosyltransferase
- methylmalonic aciduria (cobalamin deficiency) type B