Lactic acidosis in childhood: Part II

Bilateral infantile cataractogenesis in a patient with deficiency of complex I, a mitochondrial electron transport chain enzyme

Progressive bilateral cataracts developed in infancy in a 5-month-old girl with deficiency of complex I, a mitochondrial electron transport chain enzyme. In the newborn period, she had severe lactic acidosis and the diagnosis of complex I deficiency was confirmed by mitochondrial respiratory chain assay on muscle biopsy. By 5 months, she had completely opaque nuclear sclerotic cataracts, with loss of fixation and the red reflex. She underwent bilateral, sequential cataract extraction. The lens aspirate was submitted for cytologic analysis and electron microscopy, which revealed increased intracellular glycogen and swollen mitochondria. To our knowledge the association of complex I deficiency with cataracts in infancy has not been reported previously. The diagnosis of a respiratory chain enzyme defect in infancy is an indication for early ophthalmic evaluation to identify cataracts that may result in visual loss. Conversely, the recognition of cataracts in infants with unexplained neurologic disease or metabolic acidosis may necessitate further evaluation for metabolic etiologies, including mitochondrial disorders.

Approach to diagnosis of oxidative metabolism disorders

Mitochondrial oxidation of a variety of substrates produces the bulk of energy requirements for most cell types. Impairment of oxidative metabolism may result in a broad spectrum of clinical signs and symptoms. A disorder of oxidative metabolism should be suspected when an unexplained association of signs and symptoms occurs, particularly when it is progressive, involving organs with no common embryologic origin. Encephalopathy and myopathy are a particularly suspect combination. Numerous specific disorders affect oxidative metabolism. Lactate elevation frequently occurs and additional laboratory abnormalities often assist in focusing investigation. Diagnostic specificity may require, in addition to the blood and urine studies, tissue sampling, cerebral imaging, in vivo studies of tissue energetics, or molecular genetic analysis.

Oral glucose lactate stimulation test in mitochondrial disease

We selected 23 patients with neurologic diseases, including 15 boys and 8 girls from 1 month to 10 years of age, who were divided into mitochondrial and nonmitochondrial disease groups. All patients were required to fast and rest for at least 4-10 hours before the test. Glucose was administered orally using a 50% glucose:water solution at a dose of 1.75 mg/kg. Blood samples then were drawn from a retained heparinized venous line at 0, 30, 60, 120, and 180 min and tested for lactate and glucose levels. Of the mitochondrial disease group, 10 of 11 patients had an upward sloping curve of lactate metabolism; the one who had a flat line response was a patient who suffered from a free-fatty-acid metabolic defect presenting with a recurrent Reye-like syndrome. There was a relatively flat line response in the nonmitochondrial disease group except in a patient with alternating hemiplegia whose symptoms responded well to flunarizine therapy. A significant increase in blood lactate content at 60 min after glucose loading occurred in the mitochondrial disease group, in contrast to that of the nonmitochondrial group. Sensitivity and specificity of a 5 mg/dl increase in blood lactate concentration at 60 min was 72.7% vs. 91.7% Moreover, all 4 patients whose blood lactate increased by 13 mg/dl at 60 min were in the mitochondrial disease group.

Detection of inherited neurometabolic disorders. A practical clinical approach

The most common neurometabolic disorders to be considered are organic acidurias and amino acid apathies followed by urea cycle disorders, congenital lactic acidosis, peroxisomal disorders, and, less frequently, sphingolipidoses, mucopolysaccharidoses, glycoprotein degradation disorders, fatty acid oxidation disorders, and neuronal ceroid lipofuscinoses.

Mitochondrial encephalomyopathies in childhood. I. Biochemical and morphologic investigations

During a 4-year period (1984 to 1988), 50 children referred with manifestations of central nervous system or neuromuscular disease combined with hyperlactatemia were subjected to investigations that aimed to identify and characterize children with mitochondrial disorders. Biochemical and morphologic investigations of quadriceps muscle biopsy tissue were done, including oximetric and spectrophotometric analysis of the respiratory chain function, enzyme histochemistry, electron microscopy, and analysis of mitochondrial DNA. A diagnosis of mitochondrial disease was based on the presence of at least two of five criteria: (1) abnormal results of oximetry, (2) abnormal results of spectrophotometry, (3) enzyme histochemical evidence of cytochrome x oxidase deficiency, (4) deletions or point mutations of mitochondrial DNA, and (5) abundant ultrastructurally abnormal mitochondria. With the combined biochemical and morphologic investigation, 20 of the children were found to have mitochondrial disorders. In an additional 10 children a mitochondrial disorder was neither excluded nor verified. Mitochondrial disorders are thus an important cause of central nervous system and neuromuscular disease in children with hyperlactatemia.