In Dravet Syndrome, how does the Naᵥ1.1 channel dysfunction affect neuronal networks in the developing brain?

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Question restatement: In Dravet Syndrome, how does the Naᵥ1.1 channel dysfunction affect neuronal networks in the developing brain?

Option 1: 'Delayed maturation of potassium channels increases resting membrane potential, causing excitotoxicity.' While potassium channel maturation can influence excitability, this statement misattributes the primary mechanism in Dravet syndrome, which centers on Naᵥ1.1 (SCN1A) dysfunction in interneurons rather than a direct, isolated effect on potassium channel maturation. It also implies a direct increase in resting potential leading to excitotoxicity, which is not the established pathophysiology for this channel defect.

Option 2: 'Increased action potential frequency in inhibitory neurons causes seizure termination.' This option describes heightened activity in inhibitory neurons as a mechanism for stopping seizures, which contradicts the known situation in Dravet syndrome. Naᵥ1.1 dysfunction typically reduces the excitability of inhibitory interneurons, not increases it; thus, this would not plausibly explain seizure termination and is inconsistent with the disease model.

Option 3: 'Dysfunctional Naᵥ1.1 in inhibitory interneurons leads to insufficient GABA release and unbalanced excitability.' This statement aligns with the widely accepted mechanism of Dravet syndrome: loss or dysfunction of Naᵥ1.1 in GABAergic interneurons reduces their firing, decreasing inhibitory GABA release, and thereby tipping the balance toward network hyperexcitability and seizures in the developing brain. The idea of disinhibition leading to network instability fits the observed phenotype.

Option 4: 'Impaired depolarization of excitatory neurons reduces cortical activity.' While excitatory neuron depolarization is essential for cortical signaling, Dravet syndrome is primarily driven by impaired inhibitory interneuron function due to Naᵥ1.1 defects. This choice misplaces the effect, emphasizing reduced activity in excitatory neurons rather than the key disinhibitory mechanism arising from interneuron dysfunction. It does not capture the core pathophysiology linked to Naᵥ1.1 loss of function in inhibitory circuits.

In summary, the central concept is that Naᵥ1.1 channel dysfunction in inhibitory interneurons diminishes GABAergic inhibition, leading to an imbalance that favors excitatory activity and seizure propensity during brain development, rather than primarily altering potassium channel maturation, increasing inhibitory neuron firing, or suppressing excitatory neuron depolarization. The incorrect options describe scenarios that either misattribute the primary cell type affected, reverse the direction of effect, or emphasize a mechanism not supported by the established understanding of Dravet syndrome pathology.

NEUR20001_2025_SM2 Assessment for Workshop 7

In Dravet Syndrome, how does the Naᵥ1.1 channel dysfunction affect neuronal networks in the developing brain?

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