An organic acid that is found in the blood and urine. 3-Methylglutaconic aciduria is a disorder that impairs the body's ability to make energy in the mitochondria. As a result of this impairment, 3-methylglutaconic acid and 3 methylglutaric acid build up and be detected in the urine. 3-MGA type II is generally used to describe the type of 3-MGA found in organic acid profiles of those who have Barth syndrome.