3-Methylcrotonyl-CoA carboxylase deficiency is known by many names. It is also called as 3MCC deficiency, Methylcrotonylglycinuria type 1, or BMCC. This is a disorder that can be inherited where the human body becomes incapable of properly processing some proteins. Those who suffer from this deficiency have an insufficient supply of leucine-breaking enzyme. Leucine is an amino acid which is a protein base.