Respiratory chain complex I deficiency in an infant with Ohtahara syndrome

[Difficulties in the diagnosis, prognosis and treatment of genetic epileptic encephalopathies: the view of a neurologist]

Genetic epileptic encephalopathies are a rather wide spectrum of childhood epilepsies with onset of epilepsy in the first 1.5-2 years of life, regression or delayed psychomotor and speech development and 'massive' epileptiform activity on electroencephalogram (EEG). The review discusses the difficulties of choosing the optimal method of genetic examination, problems with the interpretation of the results obtained, the formulation of the diagnosis, the determination of the prognosis of the course and targeted therapy. It is emphasized that the interpretation of the identified genetic variants is not an easy task, requiring close interaction between specialists in molecular genetics, bioinformatics, neurology and clinical genetics. The possibilities of targeted treatment of genetic epileptic encephalopathies are still limited, but knowledge of the genetic cause of epilepsy allows making a more informed choice of the treatment.

Mitochondrial Respiration in Human Colorectal and Breast Cancer Clinical Material Is Regulated Differently

We conducted quantitative cellular respiration analysis on samples taken from human breast cancer (HBC) and human colorectal cancer (HCC) patients. Respiratory capacity is not lost as a result of tumor formation and even though, functionally, complex I in HCC was found to be suppressed, it was not evident on the protein level. Additionally, metabolic control analysis was used to quantify the role of components of mitochondrial interactosome. The main rate-controlling steps in HBC are complex IV and adenine nucleotide transporter, but in HCC, complexes I and III. Our kinetic measurements confirmed previous studies that respiratory chain complexes I and III in HBC and HCC can be assembled into supercomplexes with a possible partial addition from the complex IV pool. Therefore, the kinetic method can be a useful addition in studying supercomplexes in cell lines or human samples. In addition, when results from culture cells were compared to those from clinical samples, clear differences were present, but we also detected two different types of mitochondria within clinical HBC samples, possibly linked to two-compartment metabolism. Taken together, our data show that mitochondrial respiration and regulation of mitochondrial membrane permeability have substantial differences between these two cancer types when compared to each other to their adjacent healthy tissue or to respective cell cultures.

X-linked intellectual disability gene CASK regulates postnatal brain growth in a non-cell autonomous manner

The phenotypic spectrum among girls with heterozygous mutations in the X-linked intellectual disability (XLID) gene CASK (calcium/calmodulin-dependent serine protein kinase) includes postnatal microcephaly, ponto-cerebellar hypoplasia, seizures, optic nerve hypoplasia, growth retardation and hypotonia. Although CASK knockout mice were previously reported to exhibit perinatal lethality and a 3-fold increased apoptotic rate in the brain, CASK deletion was not found to affect neuronal physiology and their electrical properties. The pathogenesis of CASK associated disorders and the potential function of CASK therefore remains unknown. Here, using Cre-LoxP mediated gene excision experiments; we demonstrate that deleting CASK specifically from mouse cerebellar neurons does not alter the cerebellar architecture or function. We demonstrate that the neuron-specific deletion of CASK in mice does not cause perinatal lethality but induces severe recurrent epileptic seizures and growth retardation before the onset of adulthood. Furthermore, we demonstrate that although neuron-specific haploinsufficiency of CASK is inconsequential, the CASK mutation associated human phenotypes are replicated with high fidelity in CASK heterozygous knockout female mice (CASK^(+/-)). These data suggest that CASK-related phenotypes are not purely neuronal in origin. Surprisingly, the observed microcephaly in CASK^(+/-) animals is not associated with a specific loss of CASK null brain cells indicating that CASK regulates postnatal brain growth in a non-cell autonomous manner. Using biochemical assay, we also demonstrate that CASK can interact with metabolic proteins. CASK knockdown in human cell lines cause reduced cellular respiration and CASK^(+/-) mice display abnormalities in muscle and brain oxidative metabolism, suggesting a novel function of CASK in metabolism. Our data implies that some phenotypic components of CASK heterozygous deletion mutation associated disorders represent systemic manifestation of metabolic stress and therefore amenable to therapeutic intervention.

The epileptic encephalopathies

The term epileptic encephalopathy refers to the condition where epileptic activity, clinical or subclinical, is thought to be responsible for any disturbance of cognition, behavior, or motor control. Although currently described as a concept that may occur in any of the epilepsies, children with the severe early onset epilepsies are thought to be more at risk than others. These epilepsies have been termed the "epileptic encephalopathies." The degree to which epileptic activity is responsible for neurodevelopmental compromise may be variable in each individual case, and the degree to which this may be reversible unclear. Data from the laboratory and the clinic may provide greater insight into the degree to which epileptic activity may contribute in individual syndromes, although much is yet to be learnt. The aim in epilepsy management remains one of seizure control; in some specific circumstances this may include subclinical epileptic activity. However, avoidance of treatment that may lead to deterioration of seizure control may be equally important.

Early-onset epileptic encephalopathies: Ohtahara syndrome and early myoclonic encephalopathy

Ohtahara syndrome and early myoclonic encephalopathy are the earliest presenting of the epileptic encephalopathies. They are typically distinguished from each other according to specific clinical and etiologic criteria. Nonetheless, considerable overlap exists between the two syndromes in terms of clinical presentation, prognosis, and electroencephalographic signature. Newer understandings of underlying etiologies of these conditions may support the previously suggested concept that they represent a single spectrum of disease rather than two distinct disorders. We review both syndromes, with particular focus on the underlying genetics and pathophysiology and implications regarding the classification of these conditions.

Epileptic seizures in infants and children with mitochondrial diseases

The purpose of this study is to describe the characteristics of epileptic seizures in infants and children with mitochondrial diseases. From 1984 to December 2010, data from 46 of 76 patients diagnosed as having mitochondrial diseases with epileptic seizures were reviewed. Age at seizure onset, epileptic phenotypes, electroencephalogram findings, magnetic resonance imaging features, and treatment outcome in patients with syndromic or nonsyndromic mitochondrial diseases were analyzed. Thirty (65%) of 46 patients manifested seizures before the age of 1 year; 43% had Leigh syndrome and 53% had nonsyndromic mitochondrial diseases. Twenty-eight (61%) of 46 patients exhibited seizures as the manifesting complaint. Nineteen (68%) of 28 patients had nonsyndromic mitochondrial diseases. The most frequently observed electroencephalogram finding was background slow activity (28/46; 61%) in both groups. The most common cortical abnormality relevant to clinical seizures was diffuse brain atrophy on the brain magnetic resonance imaging (26/45; 58%), which was commonly observed in patients with nonsyndromic mitochondrial diseases (16/26; 62%). Despite treatment, 49% of patients experienced less than 50% seizure reduction rate, 77% of whom had nonsyndromic mitochondrial diseases. Leigh syndrome and nonsyndromic mitochondrial diseases often manifest as infantile seizures. Epileptic seizure as the initial complaint, diffuse brain atrophy, and refractory epilepsy were more common in patients with nonsyndromic mitochondrial diseases.

Mitochondria and neonatal epileptic encephalopathies with suppression burst

The mitochondrion is a key cellular structure involved in many metabolic functions such as ATP synthesis by oxidative phosphorylation, tricarboxylic acid cycle or fatty acid oxidation. These pathways are fundamental for biological processes such as cell proliferation or death. In the central nervous system, mitochondria dysfunctions have been involved in many neurological diseases and age-related neurodegenerative disorders, including epilepsy, Alzheimer's and Parkinson's diseases. Mitochondrial diseases are frequently caused by a disruption of the respiratory chain. Nevertheless, other mitochondrial functions, including organellar dynamics or metabolite transport, could also be involved in such pathologies. Here we described mitochondrial dysfunctions in a very severe, intractable and relatively rare neonatal epileptic encephalopathy, the Ohtahara syndrome. This condition is characterized by neonatal onset of seizures, interictal electroencephalogram with suppression burst pattern and a very poor outcome with very severe psychomotor retardation or death. The etiology of this disease remains elusive but seems to be very heterogeneous including brain malformations, metabolic errors, transcription factor and synaptic vesicle release defects. In this review, we discuss first the Ohtahara syndrome caused by mitochondrial respiratory chain damages, suggesting that these defects could be more common than previously thought. Then, we will adress the importance of the mitochondrial glutamate carrier SLC25A22 in these pathologies, since mutations of this gene were described in two distinct families. These findings suggest that glutamate metabolism should also be considered as an important cause of the Ohtahara syndrome.

Mammalian mitochondrial complex I: biogenesis, regulation, and reactive oxygen species generation

Virtually every mammalian cell contains mitochondria. These double-membrane organelles continuously change shape and position and contain the complete metabolic machinery for the oxidative conversion of pyruvate, fatty acids, and amino acids into ATP. Mitochondria are crucially involved in cellular Ca2+ and redox homeostasis and apoptosis induction. Maintenance of mitochondrial function and integrity requires an inside-negative potential difference across the mitochondrial inner membrane. This potential is sustained by the electron-transport chain (ETC). NADH:ubiquinone oxidoreductase or complex I (CI), the first and largest protein complex of the ETC, couples the oxidation of NADH to the reduction of ubiquinone. During this process, electrons can escape from CI and react with ambient oxygen to produce superoxide and derived reactive oxygen species (ROS). Depending on the balance between their production and removal by antioxidant systems, ROS may function as signaling molecules or induce damage to a variety of biomolecules or both. The latter ultimately leads to a loss of mitochondrial and cellular function and integrity. In this review, we discuss (a) the role of CI in mitochondrial functioning; (b) the composition, structure, and biogenesis of CI; (c) regulation of CI function; (d) the role of CI in ROS generation; and (e) adaptive responses to CI deficiency.