Validation and Localization of Somatic Variants in Surgical Human Epilepsy Tissue

Presenter

Rosita Beatriz Ramirez

Campus

UMass Boston

Sponsor

Jason Roush, Honors College, UMass Boston

Schedule

Session 3, 1:30 PM - 2:15 PM [Schedule by Time][Poster Grid for Time/Location]

Location

Poster Board A80, Campus Center Auditorium, Row 4 (A61-A80) [Poster Location Map]

Abstract

Mesial temporal lobe epilepsy (MTLE) is the most prevalent type of focal epilepsy in adults and often resistant to anti-seizure medications, requiring surgery. Studies to date have not identified a significant burden of germline genetic variants in MTLE. Recently, post-zygotic mutations (i.e., somatic variants) in the hippocampus, particularly those activating the Ras/MAPK signaling pathway, have emerged as a new genetic mechanism for MTLE. Somatic variants in MTLE occur at extremely low cell-fractions, making their identification and differentiation from background sequencing noise challenging due to technical limitations. Therefore, verifying the existence of somatic variants in human epilepsy tissue is crucial in evaluating their contribution to MTLE. The primary objectives of this study are to independently confirm the presence of candidate somatic variants in human MTLE brain tissue using amplicon sequencing, while identifying the cell type(s) harboring pathogenic variants through nuclear sorting and digital droplet polymerase chain reaction (ddPCR) genotyping of neurons, oligodendrocytes, astrocytes, and microglia. Out of 130 candidate somatic variants, 102 (80%) were validated with a variant allele fraction of  0.568±0.65% (MED±IQR). Ongoing cell type characterization studies anticipate a higher fraction of mutant alleles in neurons compared to the other cell types. In summary, amplicon sequencing is an effective strategy for confirming the presence of low abundance somatic variants in MTLE tissue. By identifying the variant-positive cell types we hope to begin to understand the developmental origins of focal epilepsies and contribute to the development of novel treatment strategies for patients with drug-resistant disease. 

Keywords

Somatic Variants, Ras/MAPK Signaling Pathway, Mesial Temporal Lobe Epilepsy, Amplicon Sequencing, Focal Epilepsy

Research Area

Neuroscience and Cognitive Science

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