Neonate with benign familial neonatal convulsions: recorded generalized and focal seizures

Developmental changes in KCNQ2 and KCNQ3 expression in human brain: possible contribution to the age-dependent etiology of benign familial neonatal convulsions

Several mutations of KCNQ2 and KCNQ3 are considered to be associated with benign familial neonatal convulsions (BFNC). BFNC is characterized by seizures starting within several days of life and spontaneous remission within weeks to months. KCNQ channel is a heteromeric voltage-dependent potassium channel consisting of KCNQ2 and KCNQ3 subunits. To clarify the age-dependent etiology of BFNC, we examined the developmental changes in KCNQ2 and KCNQ3 expression in human hippocampus, temporal lobe, cerebellum and medulla oblongata obtained from 23 subjects who died at 22 gestation weeks to adulthood. Formalin-fixed and paraffin-embedded specimens were used for immunohistochemistry. Unique developmental changes in KCNQ2 and KCNQ3 were found in each region. A high expression of KCNQ2 was identified in the hippocampus, temporal cortex, cerebellar cortex and medulla oblongata in fetal life, but such expression decreased after birth. The expression of KCNQ3 increased in late fetal life to infancy. Simultaneous and high expressions of KCNQ2 and KCNQ3 were observed in each region from late fetal life to early infancy, coinciding with the time when BFNC occurs. Such coexpression may contribute to the pathogenesis of BFNC.

Epilepsy: a review of selected clinical syndromes and advances in basic science

Epilepsy is a common neurologic disorder that manifests in diverse ways. There are numerous seizure types and numerous mechanisms by which the brain generates seizures. The two hallmarks of seizure generation are hyperexcitability of neurons and hypersynchrony of neural circuits. A large variety of mechanisms alters the balance between excitation and inhibition to predispose a local or widespread region of the brain to hyperexcitability and hypersynchrony. This review discusses five clinical syndromes that have seizures as a prominent manifestation. These five syndromes differ markedly in their etiologies and clinical features, and were selected for discussion because the seizures are generated at a different 'level' of neural dysfunction in each case: (1) mutation of a specific family of ion (potassium) channels in benign familial neonatal convulsions; (2) deficiency of the protein that transports glucose into the CNS in Glut-1 deficiency; (3) aberrantly formed local neural circuits in focal cortical dysplasia; (4) synaptic reorganization of limbic circuitry in temporal lobe epilepsy; and (5) abnormal thalamocortical circuit function in childhood absence epilepsy. Despite this diversity of clinical phenotype and mechanism, these syndromes are informative as to how pathophysiological processes converge to produce brain hyperexcitability and seizures.

Neonatal seizures with tonic clonic sequences and poor developmental outcome

Seizures consisting of a tonic followed by a clonic phase have rarely been described in neonates and are not included in the current classifications of neonatal seizures. Our video archive of 105 neonates with seizures or suspected seizures revealed six neonates with such tonic clonic or tonic myoclonic sequences. Two of those neonates had pyridoxine dependent seizures. The other four neonates had drug refractory seizures and demonstrated similarities in electro-clinical pattern, clinical course and outcome. Their seizures started with tonic posturing and after 10-20s tonic posturing was superimposed by focal or multifocal cloni or myocloni. Ictal EEG started with voltage attenuation followed by bilateral or alternating focal epileptic discharges. The interictal EEG was abnormal. One child died, while the other three children became seizure free but had severe motor delay and mental retardation. In one of those three children, a de novo missense mutation was detected in the voltage gated potassium channel gene KCNQ2, indicating a genetic relationship between drug refractory neonatal seizures of unknown etiology with tonic clonic or myoclonic sequences and the well-known syndrome of benign familial neonatal convulsions (BFNC).

Age-dependent modulation of hippocampal excitability by KCNQ-channels

Recently, mutations of KCNQ2 or KCNQ3, members of the KCNQ-related K(+)-channel (KCNQ-channel) family, were identified as cause of benign familial neonatal convulsions (BFNC). However, the exact pathogenic mechanisms of age-dependent development and spontaneous remission of BFNC remain to be elucidated. To clarify the age-dependent etiology of BFNC, we determined age-dependent functional switching of KCNQ-channels, GABAergic- and glutamatergic-transmission in rat hippocampus. The effects of inhibitors of KCNQ-channel, GABA- and glutamate-receptors on propagation of neuronal-excitability and neurotransmitter release were determined by 64-channel multielectrode-dish (MED64), whole-cell recording, in vitro release technique and in vivo microdialysis biosensor, using rat hippocampus from day of birth (P0) to postnatal-day 56 (P56). Inhibition of KCNQ-channels enhanced depolarization-induced glutamate and GABA releases during P0-P7, but not during P14-P28. Inhibition of KCNQ-channels magnified neuronal-excitability propagation from P0 to P14: maximal at P3, but this effect disappeared by P28. GABA(A)-receptor inhibition surprisingly reduced neuronal-excitability propagation during P0-P3, but not at P7. AMPA/glutamate-receptors inhibition reduced propagation of neuronal-excitability throughout the study period. KCNQ-channels inhibition shortened spike-frequency adaptation, but this stimulation was more predominant during P<7 than P>14. During the first week of life, KCNQ-channels performed as a predominant inhibitory system, whereas after this period GABAergic-transmission switched from excitatory to inhibitory function. Contrary, glutamatergic-transmission has acquired as excitatory function from P0. These findings suggest that the pathogenic mechanisms of age-dependent development and spontaneous remission of BFNC are, at least partially, associated with the interaction between age-dependent reduction of inhibitory KCNQ-channel activity and age-dependent functional switching of the GABAergic-system from excitatory to inhibitory action in neonatal CNS.

Epilepsy genetics

BACKGROUND

Epilepsy genetics is a complex and rapidly expanding field that involves the contributions and collaborative efforts of geneticists, molecular biologists, epidemiologists, and clinicians.

REVIEW SUMMARY

This article first provides a background review of basic terminology and contributions from the fields of epilepsy, genetics, and genetic epidemiology. It further describes the evidence for the genetic basis of epilepsy and enumerates the linkage findings and epilepsy susceptibility genes reported to date. It then addresses existing knowledge about the genetics of electroencephalogram abnormalities and their relationship to clinical epilepsy. Finally, it gives guidelines for genetic counseling, with attention to patients' frequently asked questions.

CONCLUSIONS

This review provides a framework for understanding current and future investigations in the field of epilepsy genetics and a way to assist and educate individuals and families living with epilepsy.

Genetics of the epilepsies

Recent molecular insights into the human idiopathic epilepsies have suggested the central role of ligand-gated and voltage-gated ion channels in their etiology. So far, genes coding for sodium and potassium channel subunits as well as a nicotinic cholinergic receptor subunit have been identified for mendelian idiopathic epilepsies. In vitro and in vivo studies of mutations demonstrate functional changes, allowing new insights into mechanisms underlying hyperexcitability. Similarly, spontaneous murine epilepsy models have been associated with calcium channel molecular defects. The major challenge before us in understanding the genetics of the epilepsies is to identify genes for common forms of epilepsy following complex inheritance. Once such genes are discovered, the gene-gene-environmental interactions producing specific epilepsy syndromes can be explored.

Neonatal seizures and neonatal epileptic syndromes

The neonatal period is defined as the first 28 days of life of a term infant; for premature infants the limit of this period is 44 completed weeks of the infant's conceptional age (CA)-defined as the chronological age plus gestational age (GA) at birth. The clinical and electroencephalographic (EEG) manifestations of seizures during this period are determined primarily by the development features of the immature brain at the time of seizure onset, but are also related to the type and diversity of etiologies and risk-factors for seizures neonates may face early in life. Neonatal seizures may be strikingly different from the clinical and electrical seizures of older children and adults. In addition, findings from basic science investigations suggest that immature animals are more likely to experience seizures in response to injury than more mature animals, although the developing brain is less susceptible to seizure-induced injury.

Neonatal seizures: early-onset seizure syndromes and their consequences for development

The determination of the developmental consequences of seizure syndromes in the neonate is based upon a number of factors which include: understanding of the clinical and electroencephalographic (EEG) features of neonatal seizures; current theories of the mechanisms by which neonatal seizures are generated; a current classification of neonatal seizures; potential etiologic and risk factors for seizures; and therapies. In addition, different seizure types, mechanisms of generation and etiologies of cerebral dysfunction may vary with conceptional age of the infant. There are a few distinct neonatal epileptic syndromes, which are rare, have been well described: benign neonatal convulsions; benign neonatal familial convulsions; early myoclonic encephalopathy and early infantile epileptic encephalopathy. The prognosis for the first two is relatively good while the outcome for the other two with encephalopathy is catastrophic. However, the majority of neonatal seizures occur as acute, reactive events in association with a wide range of etiologic factors. These etiologic factors, as well as those of the more traditionally defined syndromes, are the main determinants of eventual developmental outcome of neonates who experience seizures. Although experimental data suggests that some epileptic seizures eventually may have physiological, histological, metabolic, or behavioral consequences, there is yet direct evidence in humans to suggest that the occurrence of seizures themselves in the neonate is the main determinant of long-term outcome.

Genetics of the epilepsies

Recent molecular insights into the human idiopathic epilepsies have suggested the central role of ligand-gated and voltage-gated ion channels in their etiology. So far, genes coding for sodium and potassium channel subunits as well as a nicotinic cholinergic receptor subunit have been identified for Mendelian idiopathic epilepsies. In vitro and in vivo studies of mutations demonstrate functional changes, allowing new insights in mechanisms underlying hyperexcitability. Similarly, spontaneous murine epilepsy models have been associated with calcium channel molecular defects. The major challenge before us in understanding the genetics of the epilepsies is to identify genes for common forms of epilepsy following complex inheritance. Once such genes are discovered, the gene-gene-environmental interactions producing specific epilepsy syndromes can be explored.

Benign familial neonatal epilepsy with mutations in two potassium channel genes

The significant progress made over the past year in understanding the basis for a form of neonatal seizures can be attributed to the successful positional cloning of two new voltage-gated potassium channel genes. Expression studies have increased our understanding of the biology of these channels and their role in epilepsy.

Ion channels and the genetic contribution to epilepsy

Recent application of genetic analysis to rare, hereditary epilepsies has resulted in the identification of mutations in genes encoding ion channels or functionally related proteins in several human and animal syndromes. Reviewed here are selected human and murine epilepsies that result from ion channel mutations. In humans, three autosomal-dominant disorders--benign familial neonatal convulsions, nocturnal frontal lobe epilepsy, and "generalized epilepsy with febrile seizures plus"--result from mutations affecting voltage-sensitive potassium channels, a central nicotinic acetylcholine receptor, and a voltage-sensitive sodium channel, respectively. In mice, four genetically distinct, autosomal-recessive models of absence epilepsy are caused by mutations in genes encoding three types of calcium channel subunits and a sodium-hydrogen ion exchanger. These findings suggest that variation in genes encoding ion channels could determine susceptibility to common human epilepsies.

Benign familial neonatal convulsions followed by benign epilepsy with centrotemporal spikes in two siblings

PURPOSE

To report on sibling cases with benign familial neonatal convulsions (BFNC) followed by benign epilepsy with centrotemporal spikes (BECT).

METHODS

Case histories and EEGs were obtained for the two siblings with neonatal and subsequent epileptic seizures in one pedigree with BFNC.

RESULTS

The family included six affected cases of BFNC in two generations: the proband, the proband's mother and two sisters, and the proband's maternal uncle and his daughter. The proband developed a generalized tonic convulsion 2 days after birth with no apparent cause and normal interictal EEG, and experienced a total of 18 episodes of tonic or clonic seizures or both by age 9 months. In the follow-up course, an EEG recording showed rolandic discharges at 2 years, and a sylvian seizure occurred at 4 years during sleep. On carbamazepine therapy, the last seizure was recorded at 9 years after a total of 11 episodes of sylvian seizures, with normal EEGs after 12 years. The proband's sister experienced nine episodes of brief tonic seizures between 7 and 9 days after birth, and also developed eight episodes of sylvian seizures from 4 to 7 years, with rolandic discharges on EEG until age 9 years. All of the family members had normal psychomotor development, with no neurologic sequelae.

CONCLUSIONS

This report of BFNC followed by BECT in sibling cases is significant in view of the genetic analysis and the classification of epilepsies and epileptic syndromes.

Benign familial neonatal convulsions: abnormal intrauterine movements, provocation by feeding and ICTAL EEG

An infant with benign familial neonatal convulsions had abnormal movements during the last 2 months of pregnancy suggestive of intrauterine seizures. His postnatal seizures, one of which was captured by electroencephalography, had both partial and generalized features. Most seizures appeared to be provoked by feeding.