Epilepsia partialis continua associated with NADH-coenzyme Q reductase deficiency

Mitochondrial Disease: Advances in clinical diagnosis, management, therapeutic development, and preventative strategies

PURPOSE OF REVIEW

Primary mitochondrial disease encompasses an impressive range of inherited energy deficiency disorders having highly variable molecular etiologies as well as clinical onset, severity, progression, and response to therapies of multi-system manifestations. Significant progress has been made in primary mitochondrial disease diagnostic approaches, clinical management, therapeutic options, and preventative strategies that are tailored to major mitochondrial disease phenotypes and subclasses.

RECENT FINDINGS

The extensive phenotypic pleiotropy of individual mitochondrial diseases from an organ-based perspective is reviewed. Improved consensus on standards for mitochondrial disease patient care are being complemented by emerging therapies that target specific molecular subtypes of mitochondrial disease. Reproductive counseling options now include preimplantation genetic diagnosis at the time of in vitro fertilization for familial mutations in nuclear genes and some mtDNA disorders. Mitochondrial replacement technologies have promise for some mtDNA disorders, although practical and societal challenges remain to allow their further research analyses and clinical utilization.

SUMMARY

A dramatic increase has occurred in recent years in the recognition, understanding, treatment options, and preventative strategies for primary mitochondrial disease.

The use of neuroimaging in the diagnosis of mitochondrial disease

Mutations in nuclear and mitochondrial DNA impacting mitochondrial function result in disease manifestations ranging from early death to abnormalities in all major organ systems and to symptoms that can be largely confined to muscle fatigue. The definitive diagnosis of a mitochondrial disorder can be difficult to establish. When the constellation of symptoms is suggestive of mitochondrial disease, neuroimaging features may be diagnostic and suggestive, can help direct further workup, and can help to further characterize the underlying brain abnormalities. Magnetic resonance imaging changes may be nonspecific, such as atrophy (both general and involving specific structures, such as cerebellum), more suggestive of particular disorders such as focal and often bilateral lesions confined to deep brain nuclei, or clearly characteristic of a given disorder such as stroke-like lesions that do not respect vascular boundaries in mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episode (MELAS). White matter hyperintensities with or without associated gray matter involvement may also be observed. Across patients and discrete disease subtypes (e.g., MELAS, Leigh syndrome, etc.), patterns of these features are helpful for diagnosis. However, it is also true that marked variability in expression occurs in all mitochondrial disease subtypes, illustrative of the complexity of the disease process. The present review summarizes the role of neuroimaging in the diagnosis and characterization of patients with suspected mitochondrial disease.

Kozhevnikov epilepsy: the disease and its eponym

Eponyms continue to have their place in medicine but there are pitfalls associated with their use. "Priorities" may be debatable, misattributions are not uncommon, and knowledge of the original papers is often insufficient. A. Ya. Kozhevnikov (1836-1902) is considered to be the founder of the Russian neurology, best known in the West for his work on epilepsia partialis continua (EPC), published in 1894. Kozhevnikov considered various natures for this disorder but thought chronic infectious etiology to be the most probable. Shortly the eponym Kozhevnikov epilepsy was coined and used in clinical practice and writing. Thirty-five years after Kozhevnikov's death, in 1937, a new form of viral encephalitis, Russian spring-summer tick-borne encephalitis (RTBE), was discovered, which was strongly associated with EPC and at times incorrectly attributed to Kozhevnikov by Russian (Soviet) and West-European scientists, although he never specifically identified or even could have recognized this disease entity. When, in 1958, Canadian scientists published about persisting focal epilepsy due to chronic focal encephalitis in children, a new disease was proclaimed: Rasmussen syndrome or Rasmussen chronic encephalitis. The only reference to Kozhevnikov in the Canadian papers was the incorrect suggestion that Kozhevnikov himself described EPC in RTBE. This historical error resulted in continuing misquotations of Kozhevnikov in the current literature and controversies concerning the place of Kozhevnikov epilepsy in the Classification Scheme of the International League Against Epilepsy (ILAE). The history of Kozhevnikov epilepsy thereby offers an illustrative example of the successive misunderstandings, errors, and controversies that arise due to insufficient knowledge or understanding of the original publications, questionable post hoc interpretations of earlier findings, misquoting of secondary papers, or a combination of all these.

Anticonvulsant mechanisms of the ketogenic diet

The ketogenic diet (KD) is a broadly effective treatment for medically refractory epilepsy. Despite nearly a century of use, the mechanisms underlying its clinical efficacy remain unknown. In this review, we present one intersecting view of how the KD may exert its anticonvulsant activity against the backdrop of several seemingly disparate mechanistic theories. We summarize key insights gleaned from experimental and clinical studies of the KD, and focus particular attention on the role that ketone bodies, fatty acids, and limited glucose may play in seizure control. Chronic ketosis is anticipated to modify the tricarboxcylic acid cycle to increase GABA synthesis in brain, limit reactive oxygen species (ROS) generation, and boost energy production in brain tissue. Among several direct neuro-inhibitory actions, polyunsaturated fatty acids increased after KD induce the expression of neuronal uncoupling proteins (UCPs), a collective up-regulation of numerous energy metabolism genes, and mitochondrial biogenesis. These effects further limit ROS generation and increase energy production. As a result of limited glucose and enhanced oxidative phosphorylation, reduced glycolytic flux is hypothesized to activate metabolic K(ATP) channels and hyperpolarize neurons and/or glia. Although it is unlikely that a single mechanism, however well substantiated, will explain all of the diet's clinical benefits, these diverse, coordinated changes seem poised to stabilize synaptic function and increase the resistance to seizures throughout the brain.

Mitochondrial biogenesis in the anticonvulsant mechanism of the ketogenic diet

OBJECTIVE

The full anticonvulsant effect of the ketogenic diet (KD) can require weeks to develop in rats, suggesting that altered gene expression is involved. The KD typically is used in pediatric epilepsies, but is effective also in adolescents and adults. Our goal was to use microarray and complementary technologies in adolescent rats to understand its anticonvulsant effect.

METHODS

Microarrays were used to define patterns of gene expression in the hippocampus of rats fed a KD or control diet for 3 weeks. Hippocampi from control- and KD-fed rats were also compared for the number of mitochondrial profiles in electron micrographs, the levels of selected energy metabolites and enzyme activities, and the effect of low glucose on synaptic transmission.

RESULTS

Most striking was a coordinated upregulation of all (n = 34) differentially regulated transcripts encoding energy metabolism enzymes and 39 of 42 transcripts encoding mitochondrial proteins, which was accompanied by an increased number of mitochondrial profiles, a higher phosphocreatine/creatine ratio, elevated glutamate levels, and decreased glycogen levels. Consistent with increased energy reserves, synaptic transmission in hippocampal slices from KD-fed animals was resistant to low glucose.

INTERPRETATION

These data show that a calorie-restricted KD enhances brain metabolism. We propose an anticonvulsant mechanism of the KD involving mitochondrial biogenesis leading to enhanced alternative energy stores.

Clinical applications of MR spectroscopy in epilepsy

1H and 31P spectroscopy detects relevant metabolite changes in patients with TLE. Numerous studies confirm reduction in NAA and in the ratio of PCr/Pi. In his 1999 review, Kuzniecky concluded that proton MRS, using single-voxel or chemical shift imaging, lateralizes temporal lobe epilepsy in 65% to 96% of cases, with bilateral changes seen in 35% to 45% of cases, whereas phosphorus MRS shows a lateralizing PCr/Pi ratio in 65% to 75% of the TLE patients. There are indications that these changes are reversible with seizure treatment. Improvements in MRS technology, such as the ability to calculate absolute concentrations, to account for differences be-tween gray and white matter and to achieve better spectral resolution by use of a higher magnetic field strength, will now allow more extensive use of this technique for patients with epilepsy.

Cortical myoclonus in children

Cortical myoclonus is a distinct clinical condition that can be defined electrophysiologically, and occurs in both children and adults. It is well known that patients sometimes exhibit stimulus-sensitive jerks and giant somatosensory-evoked potentials (SEPs). In contrast, imaging abnormalities are less prominent in many patients. Reports focusing on cortical myoclonus, except for epilepsia partialis continua, in childhood have been limited in Japan. One reason for this could be that Japanese pediatric neurologists are not familiar with the backaveraging technique. We describe the clinical and physiological features of cortical myoclonus in ten children. Routine EEG, EEG backaveraging, SEP measurement, CT/MRI (computed tomography/magnetic resonance imaging), and TMS (transcranial magnetic stimulation) were performed. All patients exhibited clear evidence of cortical myoclonus. In six patients, backaveraging was necessary since spikes were absent on routine EEG. A cortical source of the myoclonus was further supported by a TMS study performed on four patients. The etiologies of the myoclonus were diverse, cerebrovascular disease being the most common (three patients). Stimulus-sensitive or action-induced jerks were observed in three patients. Cortical SEPs were enlarged in one patient, and reduced or absent in six. Lesions were found on CT/MRI in nine patients, in five of whom the margin of the lesion was within, or adjacent to, the sensorimotor cortex. Complete destruction of the sensorimotor cortex was not observed. It was suggested that cortical neurons in the vicinity of a lesion, rather than in the lesion itself, play a role in the generation of focal myoclonus.

Hypothalamic digoxin--central role in conscious perception, neuroimmunoendocrine integration and coordination of cellular function--relation to hemispheric dominance

A family with a high prevalence of Parkinson's disease, schizophrenia, neoplasms, syndrome-X, rheumatoid arthritis and epilepsy has been described. The psychological behavioural patterns of the family were as follows--creativity and high IQ, hypersexual behaviour, reduced appetite and eating behaviour, insomnia and reduced sleep patterns, increased tendency for spirituality, increased tendency for addiction, less of bonding and affectionate behaviour and left handedness. Digoxin, an endogenous Na(+)-K(+) ATPase inhibitor secreted by the hypothalamus, was found to be elevated and RBC membrane Na(+)-K(+) ATPase activity was found to be reduced in all the disorders and in the indexed family studied. Hypothalamic digoxin can modulate conscious perception and its dysfunction may lead to schizophrenia. Digoxin can also preferentially upregulate tryptophan transport over tyrosine resulting in increased levels of depolarising tryptophan catabolites - serotonin, quinolinic acid, strychnine and nicotine and decreased levels of hyperpolarising tyrosine catabolites dopamine, noradrenaline and morphine contributing to membrane Na(+)-K(+) ATPase inhibition in all the above disorders and the indexed family. Digoxin induced membrane Na(+)-K(+) ATPase inhibition can result in increased intracellular Ca(2+) and reduced Mg(++) levels leading to glutamate excitotoxicity, oncogene activation and immune activation. Digoxin induced altered Ca(++)/Mg(++) ratios, reduced ubiquinone and increased dolichol can affect glycoconjugate metabolism, membrane formation and structure and mitochondrial function leading to the diverse disorders described above including those in the indexed family. The isoprenoid pathway and neurotransmitter patterns were compared in right-handed/left hemispheric dominant and left-handed/right hemispheric dominant individuals. The biochemical patterns in the indexed family and the diverse disorders studied correlated with those obtained in right hemispheric dominance. The hyperdigoxinemic state indicates right hemispheric dominance. Hypothalamic digoxin can thus function as the master conductor of the neuroimmunoendocrine orchestra and co-ordinate the functions of various cellular organelles.

Epilepsia partialis continua associated with widespread gliomatosis cerebri

We report an uncommon association of intractable epilepsia partialis continua that was the main presentation of widespread gliomatosis cerebri in two females. Both children had a preceding prolonged secondary generalized seizure 2-4 months before the evolution of epilepsia partialis continua, including recurrent clusters of left-sided myoclonic twitching and sensory impairment. During these events, the children remained fully alert. These seizures were corroborated by prolonged focal epileptic spike/wave discharges evident on the electroencephalograms. Cerebral magnetic resonance imaging in the first patient demonstrated a wide area of increasing signals over the right frontocentral regions, along with diffuse cortical-subcortical infiltration impinging on the left hemisphere. In the second patient a cortical lesion was suspected. Evaluation for Rasmussen's encephalitis, focal cortical dysplasia, or a gliomatous process was conducted; the patients underwent a stereotactic brain biopsy in which the histologic findings were compatible with gliomatosis cerebri with diffuse widespread infiltration of glioma cells with no constitution of a circumscribed tumor mass. The first patient was treated with cranial radiation, chemotherapy, steroids, and combined antiepileptic therapy. The focal seizures gradually but markedly decreased in frequency, and sensory impairment abated within 18 months after establishment of the diagnosis and ensuing therapy. Cognition remains intact. The second female died 2 years after presentation despite massive chemotherapy and antiepileptic medications. Although rare, gliomatosis cerebri should be taken into account in the differential diagnosis of epilepsia partialis continua in children to facilitate a rapid diagnosis and initiation of prompt treatment of this rare disorder that may respond to a concurrent effective combination of cranial radiation, chemotherapy, and antiepileptic medications.

Epilepsia partialis continua associated with a homoplasmic mitochondrial tRNA(Ser(UCN)) mutation

Epilepsia partialis continua (EPC) is a rare epileptic syndrome characterized by continuous focal seizures. We report on a 16-year-old girl who died of prolonged pharmacoresistant EPC in whom we identified a 7472insC mutation within the mitochondrial transfer ribonucleic acid (tRNA)(ser(UCN)). Additional symptoms included ataxia, lactic acidosis, myopathy, sensorineural hearing loss, severe headaches, and mental retardation. Quantification revealed 100% mutant mitochondrial DNA (mtDNA) in the patient, 4% in her mother, and none in her half-sister. This highly skewed mtDNA distribution is most improbable (approximately 3 x 10(-30)) if only explained by random genetic drift. Clustering of dysfunctional mitochondria and replicatory advantage of mutant mtDNA may play a role in the rapid segregation towards homoplasmy within one generation.