3-Methylglutaconic aciduria (MGA) is any of at least five metabolic disorders that impair the body's ability to make energy in the mitochondria.

[citation needed] There are five known subgroups of MGA; MGA type I, II, III, IV & V. The characteristic features of 3-methylglutaconic aciduria type I include speech delay, delayed development of both mental and motor skills (psychomotor delay), elevated levels of acid in the blood and tissues (metabolic acidosis), abnormal muscle tone (dystonia), and spasms and weakness affecting the arms and legs (spastic quadriparesis).

The main features of Barth syndrome include a weakened and enlarged heart (dilated cardiomyopathy), recurrent infections due to low numbers of white blood cells (neutropenia), skeletal problems, and delayed growth.

Sometimes other nervous system problems occur, such as an inability to maintain posture, poor muscle tone, the development of certain involuntary movements (extrapyramidal dysfunction), and a general decrease in brain function (cognitive deficit).

This suggests that the disease is more frequent in insular areas where there is more likelihood that both parents are carriers, a higher birth rate, and a greater frequency of consanguineous marriages.