A case of complex I deficiency with episodic respiratory distress

: A 7-year-old girl with normal psychomotor development during infancy began to have easy fatigability about 3 years of age. At the age of 5 years, she developed respiratory distress and became unconscious when the serum lactate and pyruvate levels were markedly elevated and a blood gas analysis showed respiratory and metabolic acidosis. Thereafter, she had similar episodic respiratory problems with lactic acidosis. Her muscle biopsy showed a myopathic pattern and numerous ragged-red fibers in an approximately half of muscle fibers. Lipid droplets were slightly to moderately increased in amount mostly in the ragged-red fibers. A biochemical analysis on the isolated mitochondria from the biopsied sample showed markedly decreased NADH cytochrome c reductase activity with no specific but rather uniformly decreased subunits of complex I by the immunoblotting method. She was diagnosed as having the myopathic form of complex I deficiency because she and her relatives with similar muscle symptoms had no central nervous system symptoms such as progressive mental deterioration, convulsions and stroke-like episodes. Diagnosis of complex I deficiency was further confirmed by an oxograph study; the oxygen consumption was not detectable when malate and pyruvate were added as the substrates in the isolated mitochondria. Although stroke-like episodes and convulsions are commonly seen in complex I deficiency, episodic respiratory distress as seen in the present patient has not been described in the literature.