Benign familial neonatal convulsions: generalized epilepsy?

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.

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.

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.

Partial cosegregation of familial hemiplegic migraine and a benign familial infantile epileptic syndrome

PURPOSE

We studied a large Dutch-Canadian family, in which two very rare hereditary paroxysmal neurologic disorders, familial hemiplegic migraine (FHM) and a "benign familial infantile epileptic syndrome" concur and partially cosegregate. FHM is a dominantly inherited subtype of migraine with attacks of hemiparesis, linked to chromosome 19p13 in 50% of the families tested. Recently mutations in a brain-specific P/Q-type Ca2+ channel alpha1 subunit gene (CACNL1A4) were identified in families with chromosome 19-linked FHM. The infantile epileptic syndrome resembles to two other dominantly inherited benign epilepsies occurring in the first year of life, benign familial neonatal convulsions (BFNC), assigned to chromosomes 20q13.2 and 8q, and benign infantile familial convulsions (BIFC), as yet unlinked.

METHODS

Linkage analysis was performed for the known locations of FHM and BFNC. The question whether the two conditions in this family can be caused by a single gene defect was addressed by additional linkage analysis.

RESULTS

We excluded linkage of the infantile convulsions to markers on chromosome 20q13.2, 8q, or 19p13. This indicates the existence of a third locus for benign familial convulsions in the first year of life. Linkage of FHM to these markers was not formally excluded but seems very unlikely. Statistical analysis of whether, in this family, both conditions are caused by a single gene defect was inconclusive.

CONCLUSIONS

We describe a "benign familial infantile epileptic syndrome" with attacks of FHM at a later age. Further genetic studies in this family may help to unravel the genetic basis of epilepsy or migraine or both.

Recent advances and some problems in the delineation of epileptic syndromes in children

The current International Classification of Epilepsies and Epileptic Syndromes has classified a number of age-related epileptic syndromes in children, but some of these entities have not been well delineated and many syndromes not included in the International Classification have been proposed. This article is intended to supplement some of the currently listed childhood epileptic syndromes, discuss certain problems with the classification system, and review some of the proposed pediatric syndromes.

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

A neonate with benign familial neonatal convulsions is presented. Ictal electroencephalography demonstrated a seizure of right frontal onset with generalization and one of right frontal onset which remained confined to that hemisphere. Very few ictal recordings of this entity exist. In this patient a partial seizure and a seizure with generalization were recorded, emphasizing the difficulties with the present classification.