A newborn male presenting with severe respiratory insufficiency, generalized muscle weakness, and lactic acidemia is reported from the Department of Pediatrics, Nagasaki University School of Medicine, Japan. Within 27 hours after birth he was markedly hypotonic, spontaneous movements and the Moro reflex were almost absent. A respirator was necessary because of respiratory arrest and he died 75 hours after birth. At autopsy there was variation in muscle fiber size and an increased number of Type 2C fibers but no ragged-red fibers by Gomori trichrome staining. Biochemical and histochemical studies showed cytochrome c oxidase activity was decreased in skeletal muscle but not in cardiac muscle. [1]

COMMENT. The differential diagnosis of neonatal respiratory distress syndrome should include mitochondrial myopathy. The diagnosis should still be considered even in the absence of ragged-red fibers in skeletal muscle.

Two further papers concerning mitochondrial myopathy appeared in the June 1989 issue of the Annals of Neurology. Shimozumi H et al established cultured myogenic cell lines that were defective in cytochrome c oxidase enzyme from a patient with mitochondrial encephalomyelopathy. Two kinds of myogenic cell lines, one with and one without defective enzymatic activity were demonstrated showing that a partial enzyme defect is the result of the cellular mosaicism in the tissue. The authors comment that these cloned cell lines provide an excellent system for clarifying the cause of mitochondrial myopathy and for investigating the genetic factors.

Sakuta R and Nonaka I examined muscle taken at biopsy in six patients with complex I deficiency and one patient with the clinical characteristics of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). Striking abnormalities in the blood vessels were shown by electron microscopy in five patients. The authors considered that these abnormalities in small arteries might be responsible for the occasional occurence of transient cerebral ischemia causing stroke-like episodes and progressive mental deterioration in patients with mitochondrial myopathy.