Epilepsy-associated Variants of a Single SCN1A Codon exhibit Divergent Functional Properties.

Area of Science:

• Genetics and Molecular Biology
• Neuroscience
• Medical Genetics

Background:

• SCN1A gene variants are linked to epilepsy syndromes like Dravet syndrome and developmental and epileptic encephalopathy (DEE).
• Predicting the pathogenicity of SCN1A variants is challenging due to limited training data.
• Understanding variant function is crucial for correlating genotype with phenotype in epilepsy.

Purpose of the Study:

• To investigate the functional properties of four epilepsy-associated SCN1A variants affecting the same codon (I1347).
• To correlate observed channel dysfunction with clinical phenotypes in patients.
• To improve strategies for predicting SCN1A variant pathogenicity.

Main Methods:

• Whole-cell manual patch-clamp recordings were used to assess the function of heterologously-expressed Na_V1.1 variants.
• Structural modeling utilizing AlphaFold 3 was performed to analyze protein structure.
• Clinical data from an individual with DEE and literature/ClinVar cases were analyzed.

Main Results:

• Four variants at codon I1347 (I1347T, I1347N, I1347V, I1347F) were studied in an individual with early infantile DEE and literature cases.
• Variants I1347T, I1347V, and I1347F exhibited mixed loss and gain-of-function properties.
• Variant I1347N demonstrated complete loss-of-function, with structural models indicating significant disruption of protein interactions.

Conclusions:

• SCN1A variants at the same codon can lead to divergent functional effects, impacting epilepsy phenotypes.
• Predicting the specific functional consequences of SCN1A variants should not solely rely on their position within the protein.
• These findings highlight the complexity of SCN1A-related epilepsies and the need for nuanced diagnostic approaches.