3-Methylcrotonyl-CoA carboxylase deficiency (3-MCC) is a rare genetic condition resulting from a mutation (error) in a person’s DNA. 3-MCC is an organic acid condition because it may lead to harmful amounts of certain organic acids and toxins 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 acid 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 organic acids build up in our system. 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, 3-methylcrotonyl-CoA carboxylase, is unable to break down the amino acid, leucine.
3-MCC is an autosomal recessive condition. Symptoms may begin to show during infancy, childhood, or even adulthood. A few people may never show any symptoms. Symptoms include poor appetite, tiredness, behavior changes, irritability, muscle weakness, vomiting, muscle tightness, delayed growth, or developmental delays. These signs may appear when a child eats certain food. Many of these complications may be prevented with early detection and a low-protein diet and appropriate supplements, like L-carnitine. Many babies are screened at birth so that 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.