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Our knowledge of molecular mechanisms underlying mitochondrial disorders in humans has increased considerably during the past two decades. Mitochondrial encephalomyopathies have sporadically been reported in dogs. However, molecular and biochemical data that would lend credence to the suspected mitochondrial origin are largely missing. This study was aimed to characterise a Leigh-like subacute necrotising encephalopathy (SNE) in Yorkshire Terriers and to shed light on its enzymatic and genetic background. The possible resemblance to SNE in Alaskan Huskies and to human Leigh syndrome (LS) was another focus of interest. Eleven terriers with imaging and/or gross evidence of V-shaped, non-contiguous, cyst-like cavitations in the striatum, thalamus and brain stem were included. Neuropathological examinations focussed on muscle, brain pathology and mitochondrial ultrastructure. Further investigations encompassed respiratory-chain activities and the mitochondrial DNA. In contrast to mild non-specific muscle findings, brain pathology featured the stereotypic triad of necrotising grey matter lesions with relative preservation of neurons in the aforementioned regions, multiple cerebral infarcts, and severe patchy Purkinje-cell degeneration in the cerebellar vermis. Two dogs revealed a reduced activity of respiratory-chain-complexes I and IV. Genetic analyses obtained a neutral tRNA-Leu(UUR) A-G-transition only. Neuropathologically, SNE in Yorkshire Terriers is nearly identical to the Alaskan Husky form and very similar to human LS. This study, for the first time, demonstrated that canine SNE can be associated with a combined respiratory chain defect. Mitochondrial tRNA mutations and large genetic rearrangements were excluded as underlying aetiology. Further studies, amongst relevant candidates, should focus on nuclear encoded transcription and translation factors.

The 8993 T>G mutation in mitochondrial DNA has been associated with variable syndromes of differing severity ranging from maternally inherited Leigh's syndrome (MILS) to neuropathy, ataxia, retinitis pigmentosa (NARP), depending on the mutation loads in affected patients. We report a kindred with several members in the same generation suffering NARP or Leigh's syndrome due to a 8993 T>G mutation. Post-mortem studies of the brain in one affected member clinically presenting with a neurological disorder intermediate between adult Leigh's syndrome and NARP showed symmetrical lesions of the basal ganglia and brainstem closely resembling those usually described in typical Leigh's syndrome. Analysis of mtDNA in different tissues showed a high proportion of mutant genome in brainstem, cerebral cortex, putamen, cerebellum and thalamus. These observations illustrate the continuum of clinical and neuropathological manifestations associated with the 8993 T>G mutation of the mtDNA.

Five unrelated patients harboring the A3243G mutation in the mitochondrial DNA (mtDNA) but presenting with different clinical phenotype were studied for their percentage of mutation at the single muscle fiber levels. One patient had a clinically and pathologically defined Leigh syndrome (LS), two showed mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS), another showed progressive external ophthalmoplegia (PEO), and the other showed mitochondrial diabetes mellitus (MDM). The mutation load was greater in the muscle from the patient with LS (92%), who showed more than 80% even in the non-ragged red fibers (RRF) and also presented the highest proportion of RRF. The patients with MELAS had lower mutation levels as well as a lower proportion of RRF, and these two parameters were even lower in the PEO and MDM patients. These results were consistent with the concept that differences in the mutation load and in the somatic distribution of the mutation among different cells and tissues are responsible for the differences in phenotypical expression of the disease.

Adult onset Leigh syndrome with a nucleotide (nt) 8993 mutation in mitochondrial (mt) DNA is reported. A 43-year-old woman with a 6-year-history of insulin-resistant diabetes mellitus developed muscular weakness, intractable nausea and vomiting, and anemia. These were followed vertigo, blindness, and deafness with nystagmus. Magnetic resonance imaging (MRI) revealed abnormal high intensities in the bilateral medial regions of the thalamus and periaqueductal gray matters. Autopsy disclosed well-demarcated necrotizing lesions with prominent capillaries in the areas detected by MRI, which were sufficiently diagnostic for Leigh syndrome. MtDNA analysis performed on DNAs extracted from formalin-fixed tissues including liver, heart, brain, muscle, kidney and pancreas showed a T-->G mutation at nt 8993. This is the first case of adult Leigh syndrome demonstrating on mtDNA mutations.

A vacuolar degeneration affecting primarily the gray matter in the central nervous system (CNS) of young Australian Cattle Dogs is described. An initial presentation of seizures was followed by a progressive spastic tetraparesis. Grossly evident bilateral and symmetrical foci of malacia were in the nuclei of the cerebellum and brain stem and the gray matter of the spinal cord. Microscopically, vacuolation of glial cells, dilation of the myelin sheaths and reactive astrocytosis characterized mild CNS changes. More advanced lesions displayed progressive dissolution of the neuropil, prominent vacuolation of reactive astrocytes, numerous glial fibrillary acidic protein-positive coiled astrocytic processes, neuronal vacuolation and loss with relative sparing of large neurons. Ultrastructurally marked mitochondrial accumulation and swelling were seen in astrocytes. In the appendicular muscles, changes interpreted as long-term denervation atrophy accompanied by widespread expression of the neonatal isoform of myosin were observed. The character of the neurological sings, the nature and the distribution of the lesions within the neuroaxis have not been reported in domestic animals. An inherited biochemical defect, possibly mitochondrial, is proposed as the cause. Selected conditions with a bilateral and symmetrical distribution affecting the gray matter of domestic animals are summarized.

Pearson's syndrome is a disease of refractory sideroblastic anemia and exocrine pancreatic dysfunction due to abnormal mitochondrial DNA (mtDNA). A male infant with Pearson's syndrome developed necrosis of both thalami and basal ganglia when he suffered from gastroenteritis at 1 year and 11 months of age. He died of sepsis at the age of 2 years and 4 months. Analysis of mtDNA from various organs revealed abnormal mtDNA with deletion by 5 kbp, confirming the diagnosis. At autopsy, the brain had symmetrical cavities in putamen, caudate nuclei and medial nuclei of the thalami. Ferruginous granules in nerve cells in medial thalamic nuclei, and scattered round bodies with neuronophagia in lateral nuclei were found at light microscopic observation. Electron microscopy showed that these granules were composed of radiating spicules and a dense layer containing packed cytoplasmic organelles, respectively. The macroscopic distribution of brain lesions was very similar to and characteristic of Leigh's disease. This similarity leads to the supposition that defective intracellular energy utilization common to Leigh's disease could be responsible for brain lesions in this case. Although the histological appearance was somewhat atypical for Leigh's disease, very acute formation of brain lesions in this case was thought to have caused the histological difference.

The populations of cytochrome c oxidase (CCO)-positive and -negative mitochondria were analyzed in the elongated cells containing occasional multiple nuclei (myotubes) in primary muscle cultures derived from patients with various forms of mitochondrial encephalomyopathies with CCO deficiency. Even in control muscle cultures, CCO-positive (79.7%) and -negative (20.3%) mitochondria were distributed randomly, showing intracellular mosaicism. All mitochondria in all muscle cultures from two patients with clinical characteristics of Leigh's disease exhibited faint to negative CCO activity. In these patients no enzyme activity could be detected in any tissue including intrafusal fibers and fibroblasts in muscle biopsies. In patients with the fatal infantile and the encephalomyopathic forms of CCO deficiency, and myoclonic epilepsy with ragged-red fibers, two different types of myotubes containing mostly CCO-positive mitochondria and only negative mitochondria, respectively, representing intercellular mosaicism, were demonstrated. The intercellular mosaicism in biopsied and cultured muscles in the case of CCO deficiency supports the contention that both CCO-positive and -negative mitochondria coexist in the early myogenic cell and are later randomly segregated during cell division (mitotic segregation), forming two different cells.

A novel type of non-viral cytoplasmic inclusion is described, which was seen in virtually every neuron in the brain and spinal cord of a child with a presumed metabolic disorder whose clinical picture and CNS pathology were compatible with Leigh Syndrome. The ovoid to round inclusions were sharply demarcated, measuring up to 11 microns in diameter. They showed no distinctive staining with a battery of routine histological techniques. The ultrastructural features are unique, comprising non-membrane-bounded aggregates of randomly oriented plate-like structures with parallel linear densities depicting a periodicity of 11-16 nm. Immunocytochemical studies revealed strong staining with antisera to tropomyosin and weaker staining with antisera to actin. There was no reactivity with antibodies against neurofilaments, microtubules and their associated proteins, paired helical filaments, ubiquitin, vinculin or alpha-actinin. It is postulated that the metabolic disorder resulted in a neurodegenerative condition which manifested pathologically with lesions compatible with those of Leigh Syndrome. Associated with the condition was the discrete accumulation of cytoplasmic proteinaceous components, including tropomyosin, in the form of neuronal cytoplasmic inclusions possibly resulting from an alteration of the neuronal cytoskeleton.

A new patient with Leigh's syndrome (subacute necrotizing encephalomyelopathy due to pyruvate dehydrogenase complex deficiency) is presented. A Turkish boy of consanguinously married healthy parents developed progressive muscle weakness since infancy. At the age of 3 years he was unable to sit, stand or walk. Clinical examination showed general muscle weakness, hypotonia, muscle hypotrophy, bilateral ptosis, partial bilateral external ophthalmoplegia, nystagmus, intention tremor and hypoactive tendon reflexes. The EEG showed diffuse slowing, the cerebral CT scan disclosed mild hydrocephalus e vacuo. Motor nerve conduction velocity was slightly decreased, the EMG revealed signs of neuropathy. In the biopsied muscle only a mild hypotrophy of type 2 fibres was found, no abnormal mitochondria could be detected. The sural nerve was slightly abnormal: loss of large myelinated axons, loss of unmyelinated nerves. CSF protein was elevated to 80 mg/dl, protein electrophoresis revealed the pattern of markedly impaired blood-CSF barrier. Serum lactate and pyruvate were permanently elevated. In the urine the excretion of alanine was raised. The clinical state deteriorated during intercurrent infections; somnolence, vomiting and Cheyne-Stoke's respiration occurred. At the age of 3 1/2 years the child died of pneumonia. In the liver tissue a decreased activity of the pyruvate dehydrogenase complex was found. Neuropathological examination of the brain demonstrated wide-spread changes of Leigh's spongiform encephalopathy. Several enzyme deficiencies have hitherto been associated with Leigh's syndrome: This patients confirms earlier findings that a subgroup of Leigh's syndrome is caused by pyruvate dehydrogenase complex deficiency.

Three of six siblings presented with sleep apnea between 18 and 26 months of age. Twin females and a male had normal growth and development without antecedent neurologic or apparent metabolic disorder. The females presented at 25 and 27 months respectively with irregular respiration and episodes of apnea. Twin A succumbed to an apneic episode while sleeping. Central sleep apnea was diagnosed in twin B at the Stanford Sleep Clinic. She died following an apneic episode three months after evaluation. The male presented at 18 months with fatal sleep apnea. A fourth child was evaluated for sleep apnea at 7 weeks of age with several hospitalizations before her death at 31 months. She and remaining family members were extensively studied for inherited neurologic disorders including subacute necrotizing encephalomyopathy (SANE, Leigh disease). This family with lethal sleep apnea presents an association with SANE with minimal neurologic signs and symptoms and neuropathologic involvement. Lesions were confined to the respiratory centers of the lower brain stem, making sleep apnea explicable. This child and family members tested positive or borderline for inhibitor substance thiamine triphosphate (TTP). All testing for TTP inhibitor substance was performed in Professor Jack R. Cooper's laboratory, Department of Pharmacology, Yale University School of Medicine, New Haven, Conn. These cases present an interesting and instructive lesson emphasizing the need for extensive evaluation of children with unsuspected sleep apnea with early demise.

A case of subacute necrotising encephalomyelopathy is reported with such note worthy features as early onset, dystonic manifestations and the presence of low attenuation areas in the basal ganglia on computerised tomography of the brain. Laboratory findings were normal and the diagnosis was confirmed at postmortem examination.

The clinical and postmortem findings in three cases of encephalomyeloneuropathy are reported. Two patients presented with subacute sensory neuropathy and one with amnesia and confusion. In none of these cases was a tumour detected clinically or at autopsy. Neuropathological examination showed inflammatory lesions in the brain, spinal cord and posterior root ganglia indistinguishable from encephalomyeloneuropathy occurring as a remote effect of carcinoma.