Specifically, one segment of ATP synthase allows positively charged ions, called protons, to flow across a specialized membrane inside mitochondria.

Another segment of the enzyme uses the energy created by this proton flow to convert a molecule called adenosine diphosphate (ADP) to ATP.

[9] The Fo region causes rotation of F1, which has a water-soluble component that hydrolyzes ATP and together, the F1Fo creates a pathway for movement of protons across the membrane.

[11] The stator stalk is anchored in the membrane, and acts to prevent futile rotation of the ATPase subunits relative to the rotor during coupled ATP synthesis/hydrolysis.

Because these two conditions result from the same genetic changes and can occur in different members of a single family, researchers believe that they may represent a spectrum of overlapping features instead of two distinct syndromes.

[6] Mitochondrial complex V deficiency presents with heterogeneous clinical manifestations including neuropathy, ataxia, hypertrophic cardiomyopathy.

Affected individuals may have feeding problems, slow growth, low muscle tone (hypotonia), extreme fatigue (lethargy), and developmental delay.

High levels of ammonia in the blood (hyperammonemia) can also occur in affected individuals, and in some cases result in abnormal brain function (encephalopathy) and damage to other organs.

[17] Hypertrophic cardiomyopathy, a common feature of mitochondrial complex V deficiency, is characterized by thickening (hypertrophy) of the cardiac muscle that can lead to heart failure.

[18][15] Individuals with mitochondrial complex V deficiency may also have a characteristic pattern of facial features, including a high forehead, curved eyebrows, outside corners of the eyes that point downward (downslanting palpebral fissures), a prominent bridge of the nose, low-set ears, thin lips, and a small chin (micrognathia).

An infantile form of hypertrophic cardiomyopathy, a heart disorder characterized by ventricular hypertrophy, which is usually asymmetric and often involves the interventricular septum.