3-Methylcrotonyl-CoA Carboxylase Deficiency (3-MCC)



3-methylcrotonyl-CoA carboxylase deficiency (3-MCC) is an inherited condition in which the body is unable to break down certain proteins properly, which can lead to harmful amounts of organic acids and toxins in the body. Early detection and treatment can often help children with 3-MCC lead healthy lives. Each baby with 3-MCC has a different experience. A baby might start showing signs of 3-MCC around 3 to 6 months, 3 years, or even in adulthood. Some babies can have this condition and never show any signs. Symptoms of 3-MCC include poor appetite, sleeping longer or more often, tiredness, behavior changes, irritability, muscle weakness (hypotonia), vomiting, muscle tightness (spasticity), delayed growth, and developmental delays. Many of these signs may occur when a baby eats foods the body cannot break down. Symptoms can be triggered by long periods of time without eating, illnesses, and infections.

Condition Type:

Core Conditions


3-methylcrotonyl-CoA carboxylase deficiency (3-MCC) affects 1 out of every 36,000 to 50,000 babies.

More Information for Parents:
Also known as:
  • 3-MCC
  • 3-methylcrotonylglycinuria
  • BMCC deficiency
  • Methylcrotonyl-CoA carboxylase deficiency

Core Conditions