2-Methylbutyrylglycinuria (2MBG) is a rare genetic condition resulting from a mutation (error) in a person’s DNA. 2MBG is an organic acid condition because it leads to a buildup of harmful amounts of organic acids in the body. Protein in the food we eat is broken down into amino acids or “building blocks”. We typically eat more protein than needed; therefore we often have more amino acids than we need. Enzymes (special proteins) breakdown the extra amino acids into organic acids and ammonia and then harmless products our body can get rid of. If one of the enzymes needed is missing or not working correctly, the amino acid is not broken all the way down and instead builds up in our system as organic acids. Although organic acids are only mild acids, both organic acids and ammonia can damage our bodies if too much builds up. In this case the enzyme, 2-methylbutyryl-CoA dehydrogenase, is unable to break down the amino acid, isoleucine.
2MBG is caused by mutations in the ACADSB gene and is an autosomal recessive condition. Signs of 2MBG usually begin to show during infancy, sometimes as early as a few days after birth. They may include poor appetite, sleeping longer or more often, tiredness, irritability, fever, vomiting, weak muscle tone, delayed growth, tight muscles, or developmental delays. These signs may appear when a child eats certain food. Illnesses, infections, or long periods of not eating may trigger symptoms. Treatment includes supplements and a specific diet. Many babies are screened at birth so treatment may begin early, however the conditions included in newborn screening vary state by state. For more information, visit Baby’s First Test. Talk with your doctor about the most current treatments. Support groups also are a good source of information. A genetic counselor will help you understand the genetics.