Table I. Primary human lymphoblasts with mutated AARS2 have an isolated complex IV defect. Electron transport chain enzyme activities in skeletal muscle homogenate and EBV-Lymphoblast mitochondria are expressed as %CS ratio, which represents % of the normal control mean value when expressed relative to the mitochondrial marker enzyme Citrate Synthase. Bold characters indicate clinically significant abnormal values. n.t.; not tested.

Enzyme	Skeletal Muscle (%CS Ratio)		Lymphoblasts (%CS Ratio)
	Patient	Ref. Range (n = 9)	Patient	Ref. Range (n = 6)
Complex I	52	36–167	75	78–116
Complex II	129	52–156	92	47–142
Complex III	n.t.	62–185	155	64–132
Complex IV	12	36–192	38	76–126