Malignant migrating partial seizures in infancy

KCNT1 epilepsy with migrating focal seizures shows a temporal sequence with poor outcome, high mortality and SUDEP

Data on KCNT1 epilepsy of infancy with migrating focal seizures are heterogeneous and incomplete. Kuchenbuch et al. refine the syndrome phenotype, showing a three-step temporal sequence, poor prognosis with acquired microcephaly, high prevalence of extra-neurological manifestations and early mortality, particularly due to SUDEP. Refining the electro-clinical spectrum should facilitate early diagnosis.

Epileptic Encephalopathies

PURPOSE OF REVIEW

This article reviews the manifestations and treatment of the epileptic encephalopathies, which are a heterogeneous group of disorders characterized by both seizures and neurocognitive impairment.

RECENT FINDINGS

Next-generation (exome- and genome-based) sequencing technologies are revolutionizing the identification of single-gene causes of epileptic encephalopathy but have only had a modest impact on patient-specific treatment decisions. The treatment of most forms of epileptic encephalopathy remains a particularly challenging endeavor, with therapeutic decisions chiefly driven by the electroclinical syndrome classification. Most antiseizure drugs are ineffective in the treatment of these disorders, and treatments that are effective often entail significant risk and cost.

SUMMARY

The epileptic encephalopathies continue to pose a major challenge in diagnosis and treatment, with most patients experiencing very poor outcomes, although a significant minority of patients respond to, or are even cured by, specific therapies.

Emerging role of the KCNT1 Slack channel in intellectual disability

The sodium-activated potassium KNa channels Slack and Slick are encoded by KCNT1 and KCNT2, respectively. These channels are found in neurons throughout the brain, and are responsible for a delayed outward current termed I KNa. These currents integrate into shaping neuronal excitability, as well as adaptation in response to maintained stimulation. Abnormal Slack channel activity may play a role in Fragile X syndrome, the most common cause for intellectual disability and inherited autism. Slack channels interact directly with the fragile X mental retardation protein (FMRP) and I KNa is reduced in animal models of Fragile X syndrome that lack FMRP. Human Slack mutations that alter channel activity can also lead to intellectual disability, as has been found for several childhood epileptic disorders. Ongoing research is elucidating the relationship between mutant Slack channel activity, development of early onset epilepsies and intellectual impairment. This review describes the emerging role of Slack channels in intellectual disability, coupled with an overview of the physiological role of neuronal I KNa currents.

Migrating partial seizures of infancy: expansion of the electroclinical, radiological and pathological disease spectrum

Migrating partial seizures of infancy, also known as epilepsy of infancy with migrating focal seizures, is a rare early infantile epileptic encephalopathy with poor prognosis, presenting with focal seizures in the first year of life. A national surveillance study was undertaken in conjunction with the British Paediatric Neurology Surveillance Unit to further define the clinical, pathological and molecular genetic features of this disorder. Fourteen children with migrating partial seizures of infancy were reported during the 2 year study period (estimated prevalence 0.11 per 100,000 children). The study has revealed that migrating partial seizures of infancy is associated with an expanded spectrum of clinical features (including severe gut dysmotility and a movement disorder) and electrographic features including hypsarrhythmia (associated with infantile spasms) and burst suppression. We also report novel brain imaging findings including delayed myelination with white matter hyperintensity on brain magnetic resonance imaging in one-third of the cohort, and decreased N-acetyl aspartate on magnetic resonance spectroscopy. Putaminal atrophy (on both magnetic resonance imaging and at post-mortem) was evident in one patient. Additional neuropathological findings included bilateral hippocampal gliosis and neuronal loss in two patients who had post-mortem examinations. Within this cohort, we identified two patients with mutations in the newly discovered KCNT1 gene. Comparative genomic hybridization array, SCN1A testing and genetic testing for other currently known early infantile epileptic encephalopathy genes (including PLCB1 and SLC25A22) was non-informative for the rest of the cohort.

De novo gain-of-function KCNT1 channel mutations cause malignant migrating partial seizures of infancy

Malignant migrating partial seizures of infancy (MMPSI) is a rare epileptic encephalopathy of infancy that combines pharmacoresistant seizures with developmental delay. We performed exome sequencing in three probands with MMPSI and identified de novo gain-of-function mutations affecting the C-terminal domain of the KCNT1 potassium channel. We sequenced KCNT1 in 9 additional individuals with MMPSI and identified mutations in 4 of them, in total identifying mutations in 6 out of 12 unrelated affected individuals. Functional studies showed that the mutations led to constitutive activation of the channel, mimicking the effects of phosphorylation of the C-terminal domain by protein kinase C. In addition to regulating ion flux, KCNT1 has a non-conducting function, as its C terminus interacts with cytoplasmic proteins involved in developmental signaling pathways. These results provide a focus for future diagnostic approaches and research for this devastating condition.

A case of malignant migrating partial seizures in infancy as a continuum of infantile epileptic encephalopathy

The syndrome of malignant migrating partial seizures in infancy (MMPSI) is characterized by onset before the age of 6 months, nearly continuous electrographic seizures involving multiple independent areas of onset in both hemispheres, and poor developmental outcome. This report presents a case involving a patient with MMPSI, who later developed West syndrome. At the age of 2 months old, he showed multifocal partial seizures, which were refractory to antiepileptic drugs. His electroencephalogram (EEG) revealed characteristic migrating multifocal epileptiform activities and neuroimaging finding was normal. The focal seizures were refractory to antiepileptic drugs and ketogenic diet. When he was 9 months old, epilepic spasms were observed with hypsarrhythmia on EEG. He also showed severe developmental delay. MMPSI may be a continuum of infantile epileptic encephalpathy and could evolve to West syndrome.

Novel SCN1A mutation in a proband with malignant migrating partial seizures of infancy

OBJECTIVE

To characterize a novel SCN1A mutation in a proband with malignant migrating partial seizures of infancy.

DESIGN

Genomic DNA was isolated from blood and submitted for commercial testing. The identified missense mutation was confirmed in brain DNA obtained at autopsy. Genomic DNA from the brain of the proband was analyzed by comparative genome hybridization, and the coding exons of SCN9A were amplified. Quantitation studies of the mutant transcript were performed.

SETTING

Children's National Medical Center and Yale University School of Medicine. PROBAND: A full-term female infant who experienced seizure onset at age 10 weeks, with progression of hemiclonic, apneic, and multifocal migrating partial seizures leading to recurrent status epilepticus and death at age 9 months.

MAIN OUTCOME MEASURES

Electroencephalographic and magnetic resonance imaging results, quantitative RNA expression, and secondary mutation test results.

RESULTS

The heterozygous missense mutation c.C5006C>A was identified by sequencing genomic DNA from blood and was confirmed in brain DNA. The resulting amino acid substitution p.A1669E alters an evolutionarily conserved residue in an intracellular linker of domain 4 of the SCN1A sodium channel protein Na(v)1.1. The mutant transcript is found to be expressed at levels comparable to the wild-type allele in brain RNA. No variation in copy number was detected in the chromosome region 2q24 containing SCN1A or elsewhere in the genome. No mutations were detected in the linked sodium channel gene SCN9A, which has been reported to act as a modifier of SCN1A mutations.

CONCLUSION

This report expands the spectrum of SCN1A epileptic channelopathies to include malignant migrating partial seizures of infancy.

Ictal patterns in children: an illustrated review

Detailed knowledge of electroencephalographic patterns accompanying epileptic seizures in children is paramount to the correct identification of epileptic seizures and syndromes. In this article, we present a review of ictal patterns of different seizure types in children, illustrating with examples collected in our video-EEG laboratory at Pequeno Príncipe Hospital.

Duplication 16p11.2 in a child with infantile seizure disorder

Submicroscopic recurrent 16p11.2 rearrangements are associated with several neurodevelopmental disorders, including autism, mental retardation, and schizophrenia. The common 16p11.2 region includes 24 known genes, of which 22 are expressed in the developing human fetal nervous system. As yet, the mechanisms leading to neurodevelopmental abnormalities and the broader phenotypes associated with deletion or duplication of 16p11.2 have not been clarified. Here we report a child with spastic quadriparesis, refractory infantile seizures, severe global developmental delay, hypotonia, and microcephaly, and a de novo 598 kb 16p11.2 microduplication. Family history is negative for any of these features in parents and immediate family members. Sequencing analyses showed no mutations in DOC2A, QPRT, and SEZ6L2, genes within the duplicated 16p11.2 region that have been implicated in neuronal function and/or seizure related phenotypes. The child's clinical course is consistent with a rare seizure disorder called malignant migrating partial seizure disorder of infancy, raising the possibility that duplication or disruption of genes in the 16p11.2 interval may contribute to this severe disorder.

Malignant migrating partial seizures in Aicardi syndrome

This article reports on a female infant with Aicardi syndrome presenting with malignant migrating partial seizures from her first day of life. Initially, unilateral tonic seizures were seen with contralateral ictal electroencephalogram findings. Typically, these tonic seizures were accompanied by head and eye deviation and were followed by a tonic seizure on the other side of the body. At 6 months of age she developed epileptic spasms. She showed no motor development, did not respond to eye contact, and was nasogastric tube-fed. The epilepsy syndrome in this child is refractory to antiepileptic treatment and there is no psychomotor development. This case expands the phenotype of this catastrophic epileptic encephalopathy and suggests that the corpus callosum is not necessary for the 'migration' of partial seizures in this syndrome.

Migrating focal seizures in infancy: analysis of the electroclinical patterns in 17 patients

We describe the electroclinical features, therapy, and long-term evolution of 17 patients with migrating focal seizures in infancy, and analyzed the charts of these patients seen between February 1985 and July 2005. Three different electroclinical patterns were recognized: (1) 8 cases with alternating simple focal motor seizures at onset. The ictal electroencephalography (EEG) pattern was characterized by recurrence of rhythmic focal spikes or rhythmic sharp activity in the Rolandic region; (2) 5 cases with complex focal seizures and progressive appearance of polymorphic delta- activity in 1 temporo-occipital region recurring independently; (3) 4 cases with focal complex seizures with motor manifestations. Ictal EEG showed flattening or fast activity in 1 frontotemporal region followed by unilateral fast poly-spikes in alternating clusters in both hemispheres. The focal seizures were refractory to antiepileptic drugs, and all patients except 3 had severe developmental delay. Migrating focal seizures in infancy is a newly defined and rare, but underrecognized, epileptic encephalopathy.

The clinical-electrographic expression of infantile seizures

PURPOSE

To describe the electro-clinical expression of seizures in infants (1-24 months).

METHODS

We reviewed the video and EEG files of all infantile seizures recorded at Children's Memorial Hospital, Chicago, IL, from 2000 to 2005. Electrographic and clinical features were entered into separate databases. The electrographic component of the database analyzed the predominant location and pattern at onset, the evolution, the termination and the duration of each seizure. The clinical data sheet included 25 items. Each seizure was assigned to a specific category according to its most prominent clinical feature, according to the opinion of both observers.

RESULTS

Thirteen seizure types were identified. In a significant number of cases, the EEG correlate could not be predicted on the basis of clinical observations only. Generalized seizures were observed, on average, at a later age than focal seizures. Excluding spasms, the mean duration of seizures was short (36 s).

CONCLUSIONS

The results of this study are useful in describing the clinical and electrographic repertoire of infantile seizures. The findings show that video-EEG recordings in infants with frequent, recurrent seizures are useful by fully allowing complete recognition of subtle events, and in fully categorizing the true nature of the ictus. Video-EEG findings and accurate seizure classification may add fundamental information with regards to epilepsy syndrome diagnosis and specific treatment options, including surgery.

Epilepsy syndromes in infancy

An increasing number of infantile epilepsy syndromes have been recognized. However, a significant number of infants (children aged 1-24 months) do not fit in any of the currently used subcategories. This article reviews the clinical presentation, electroencephalographic findings, evolution, and management of the following entities: early infantile epileptic encephalopathy, early myoclonic epilepsy, infantile spasms/West syndrome, severe myoclonic epilepsy of infancy, myoclonic-astatic epilepsy, generalized epilepsy with febrile seizures plus, malignant migrating partial seizures of infancy, hemiconvulsions-hemiplegia-epilepsy, benign myoclonic epilepsy, and benign familial/nonfamilial infantile seizures. Issues related to their classification are addressed.

Levetiracetam in a neonate with malignant migrating partial seizures

This report describes the first neonatal case of "malignant migrating partial seizures in infancy" with a positive therapeutic response to levetiracetam. This patient is the youngest reported infant with this rare syndrome, and the report provides the first documentation on levetiracetam treatment in a neonatal patient. Treatment with levetiracetam improved both ictal and interictal status. This observation also highlights the need to consider and include malignant migrating partial seizures in the differential diagnosis of early neonatal seizure disorders, even during the first hours of life.