Table 1.

Diagnostic evaluation of children with MD (n = 53).

Characteristic		Value
Male sex		32 (60)
Age at first symptom onset, years		0.95 ± 1.07
Age at diagnosis, years		3.12 ± 2.49
Lead time to diagnosis, years		2.17 ± 2.11
First symptom	Seizure	26 (49)
	Delayed development	22 (42)
	Visual disturbance	1 (2)
	Ataxia	1 (2)
	Dystonia	1 (2)
	Nystagmus	1 (2)
	Hearing impairment	1 (2)
Lactic acidosis severity	Normal	23 (43)
	Mild	22 (42)
	Moderate	7 (13)
	Severe	1 (2)
Myopathies by pathologic features	Normal	10 (19)
	One pathology	23 (43)
	Two pathologies	20 (38)
Biochemical enzyme assay	MRC I complex deficiency	48 (92)
	MRC II complex deficiency	1 (2)
	MRC IV complex deficiency	3 (6)
Syndromic diagnosis	Leigh syndrome	11 (21)
	MELAS	2 (4)
	Non-specific MD	40 (76)

Data given as total number (percentage) or mean ± SD.

MD, mitochondrial disease; MRC, mitochondrial respiratory chain; MELAS, mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes.