Dr. Kristen Park speaking at 2014 Denver KCNQ2 Cure summit professionals track at Children's Hospital of Colorado. More information at www.kcnq2cure.org

1. Epileptic Encephalopathies:
Etiologies and Mechanisms
Kristen Park, MD
Assistant Professor of Pediatrics
and Neurology
UCHSC

2. Outline
• Overview
• Etiology and Mechanisms

3. Definition
• Age dependent syndrome
• Unique types of frequent seizures
• Abnormal interictal EEG
• Heterogeneous causes
• Pharmacoresistant
• Frequently associated with developmental
impairment and/or regression

4. Epileptic Encephalopathies

5. Etiology of Encephalopathy
• Epilepsy/epileptogenesis
• Interictal abnormalities
• Underlying pathophysiology

6. Epilepsy/Epileptogenesis
• Clinical evidence
– Longitudinal study of Dravet patients did not correlate
intellectual profile with seizure control
• Early appearance of absence seizures associated with worst
developmental outcome
• 2 patients with truncation mutations followed and
demonstrated progressive cognitive decline
– Variable timing between onset of encephalopathy and
seizures in different syndromes
• Dravet, Doose vs Rett

7. Epilepsy/Epileptogenesis
• Functional data
– MRS in patients with cortical malformations
showed abnormal NAA in the epileptogenic zone
• Normal levels when seizures controlled
• In patients with ongoing seizures, anatomically
abnormal regions that were not epileptogenic
showed normal NAA
• Decrements shown in contralateral hippocampus
and thalamus
• Reversible after successful temporal lobectomy

8. Epilepsy/Epileptogenesis
• Experimental evidence
– Mirror foci
– Kindling
– Animal models
– Cellular

9. Maturation of Excitatory and
Inhibitory Neurotransmission•
From Rakhade and Jensen, 2009
Extensive plasticity
of neurotransmitter
systems occurs
during early
postnatal
development
• This plasticity is
activity-dependent
and critically
important for normal
“critical periods” for
learning that may be
disrupted by early-life
seizure activity

10. Epileptogenesis: Synaptic Plasticity
• Molecular
– Increased Inhibitory Neurotransmission
• Accelerated changes in chloride gradient
• Increased postsynaptic GABAA receptor expression
– Altered Excitatory Neurotransmission
• Post-translational changes in GluR1 and GluR2
• Decreased dendritic spine density
• Reduced AMPA and NMDA receptor expression

11. Inhibitory Neurotransmission
• GABA is the main inhibitory
transmitter in mature neurons
• GABAA receptors mediate most fast-synaptic
inhibition
• Different subtypes confer
distinct receptor function and
pharmacology
• Undergoes developmental
changes including alteration of
GABA reversal potential (EGABA)
and changes in subunit
expression
• Enhancement of GABAA
receptor function with
benzodiazepines disrupts LTP
and memory formation and
diminishes anxiety and learned
fear responses
• GABAA receptor a1 subunit is a
key regulator of “critical
periods” for cortical plasticity
a1–6, b1–3, g1–3,
d, e, p, and q
1. Del Cerro et al., 1992; Sarter et al., 1995; Seabrook et al., 1997. 2. Vicini and Ortinski, 2004;
Corcoran et al., 2005. 3. Rudolph and Mohler, 2004. 4. Fagiolini et al., 2004. 5. Hsu et al., 2003.

12. Inhibitory Neurotransmission
• Depolarizing GABA currents are critical for Ca++
dependent developmental processes including neuronal
proliferation, migration, targeting & synaptogenesis
• Early-life seizures accelerate the switch of EGABA from
depolarizing to hyperpolarizing in hippocampal CA1
neurons and are associated with spatial learning deficits
• GABAA receptor changes after prolonged early-life
seizures
– Total GABAA receptor and a-1 subunit expression is
increased

13. Excitatory Neurotransmission
• Extensive plasticity of excitatory neurotransmission occurs during
normal postnatal development
• This plasticity is activity-dependent and can be disrupted by early-life
seizure activity
• Excitatory signaling through both the AMPA and NMDA receptors
are critical for different types of LTP and hippocampal learning
• Mutant mice lacking subtypes of AMPA receptors (GluR1 or
GluR2 subunits) or NMDA receptors have impaired learning and
behavioral abnormalities.
• Decreased AMPA Receptor GluR2 subunit expression has been
shown after hypoxia-induced seizures, Lithium-Pilocarpine-induced
seizures and febrile seizures at P10

14. Interictal Abnormalities

15. Interictal Abnormalities
• Clinical evidence
– Resections of focal cortical abnormalities in
West syndrome can lead to resolution and
improved development

16. Interictal Abnormalities
• Functional data
– EEG-fMRI studies in West syndrome
– EEG in CSWS
– fMRI studies in CSWS

17. Underlying Pathophysiology
• Clinical evidence
– Dravet
• Milder phenotypes associated with missense
mutations
• More severe phenotype associated with pore
mutations
– KCNQ2E – pore domain vs BFNC scattered
– Cognitive impairments often related to age at
onset with infantile being more severe

18. Fragile X Syndrome
• Caused by an expanded triplet repeat in the FMR1 gene
that codes for the fragile X mental retardation protein
(FMRP), an mRNA-binding protein that binds to and
regulates 4% of brain mRNA, including many RNAs
important for synaptic plasticity
• FMRP regulates mRNA transport in dendrites and
regulates local protein synthesis important for dendritic
spine development, synaptic formation and plasticity.
• In the absence of FMRP, excess and dysregulated mRNA
translation leads to altered synaptic function and loss of
protein synthesis-dependent plasticity
• The hallmark of FXS pathology is the hyperabundance of
dendritic spines with a long, thin, and otherwise immature
morphology
Comery et al., 1997; Penagarikano et al., 2007; Basel and Warren, 2008; Antar et al., 2004; Feng
et al., 1997b; Laggerbauer et al., 2001; Li et al., 2001, Lu et al.,2004; Muddashetty et al., 2007;
Zalfa et al., 2003; Gibson et al., 2008

19. Tuberous Sclerosis Complex
• Results from mutations of Hamartin
(TSC1) or Tuberin (TSC2), which
inhibit the the mammalian target of
rapamycin (mTOR) pathway and a
cascade of other downstream
kinases and translational factors
that stimulate protein translation,
cell growth and proliferation.
• TSC mutations lead to hyper-activation
of these signaling
pathways resulting in increased cell
growth, proliferation and abnormal
gene expression.
• Exact mechanisms of epilepsy and
ASD in TSC not known, but
alterations in trafficking of AMPARs,
and in expression of glutamate and
GABA-A receptors and decreases in
the glutamate transporter GLT-1
may contribute
White et al., 2001; Wong et al., 2003

20. Rett Syndrome
• Caused by mutations in the methyl-CpG
binding protein 2 (MeCP2) gene, a
transcriptional repressor involved in chromatin
remodeling and the modulation of RNA
splicing.
• In resting neurons, MeCP2 regulates gene
expression by binding to methylated CpG
dinucleotides and recruiting HDAC complexes
and chromatin remodeling proteins. This
leads to chromatin compaction, making the
promoter inaccessible to the transcriptional
machinery.
• Neuronal activity induces MeCP2
phosphorylation and leads to its release from
the promoter region, dissociation of the
corepressor complex, and transcription of
target genes.
• In Rett, the absence of MeCP2 causes a loss
of activity dependent changes in gene
expression that may disrupt synaptic plasticity
From Charhour and Zoghbi, Neuron, 2007

21. Neuroligin/Neurexin Mutations
• Neuroligins and neurexins are
proteins crucial for aligning and
activating both excitatory and
inhibitory synapses during
development.
•Mutations in a number of these
genes, and the associated Shank3
scaffolding protein, have been
implicated in autism.
•NRXN1 deletions have been
identified in a family presenting with
severe early onset epilepsy &
profound developmental delay
•An altered balance between
excitatory synapses (left) and
inhibitory (right) could affect learning
and social behavior as well as
contribute to epilepsy.
From Garber, Science 2007

22. Interneuronopathies
• Experimental evidence
– Critical role of interneurons
• Complex networks coordinate higher functions; excitatory
and inhibitory, variable firing patterns
– Developmental abnormalities resulting in reduced numbers of
cortical and hippocampal interneuron subtypes have been
reported to cause severe early life epilepsies, ID and autism:
• ARX
• NPN2
• Lissencephaly (DCX)
• SCN1A
• TSC1
• Cortical dysplasia
• PMG
• CNTNAP2

23. Interneuronopathies
• SCN1A
– Selective knock-out in basal forebrain
– Disruption of learning and memory without
spontaneous seizures
– Dysregulation of hippocampal oscillations
– Spatial learning deficit

24. Genetic effects on Synaptic Plasticity Seizure effects on Synaptic
Plasticity
Conception Birth
Neurulation Neurogenesis Max. growth
Synaptogenesis Competitive elimination
Migration from ventricular zone
Programmed cell death
Myelination
Dendritic and axonal arborization
weeks
4 8 12 16 20 24 28 32
4
months
years
2 5 18 60+
Receptor and ion channel changes

25. Application
• Characterize
– Spectrum of clinical presentation
– Functional measurements
• EEG
• Neuropsychologic profile
• Correlate
– Genotype and functional expression
– Developmental and neuroanatomic factors

26. Conclusions