A 'Two-Hit' Dual Pathway Genetic Model for Focal Cortical Dysplasia and Epilepsy
Abstract number :
3.393
Submission category :
12. Genetics / 12A. Human Studies
Year :
2019
Submission ID :
2422284
Source :
www.aesnet.org
Presentation date :
12/9/2019 1:55:12 PM
Published date :
Nov 25, 2019, 12:14 PM
Authors :
Michael S. Hildebrand, University of Melbourne; Mark F. Bennett, The Walter and Eliza Hall Institute; Sayaka Kayumi, University of Adelaide; Mark A. Corbett, University of Adelaide; Sachin Gupta, The Children's Hospital at Westmead; Zimeng Ye, University
Rationale: The “two-hit” model of genetic disease is well established in cancers. Double hits in the same gene were recently reported in two related brain malformations associated with epilepsy: TSC2 variants in hemimegalencephaly [1] and DEPDC5 variants in focal cortical dysplasia [2]. We searched for causative germline and somatic variations in siblings with focal cortical dysplasia and epilepsy to look for evidence of this two-hit model. Methods: We studied two brothers with refractory focal epilepsy and surgically resected focal cortical dysplasia (FCD type IIA). Exome sequencing was performed on blood- and brain-derived DNA to identify germline and somatic variants. Droplet digital PCR was performed for validation, and in vitro functional assays to examine the consequence of identified variants. Results: Exome analysis revealed a novel, maternally inherited germline pathogenic truncation variant (c.48delG; p.Ser17Alafs*70) in NPRL3 in both brothers. NPRL3 is a known FCD gene that encodes a negative regulator of the mTOR pathway. Somatic variant calling in brain-derived DNA from both brothers revealed a low-frequency (~2%) somatic variant (c.338C>T; p.Ala113Val) in the WNT2 gene in one brother, confirmed by digital droplet PCR. In vitro functional studies demonstrated a loss of WNT2 function associated with this variant. Conclusions: Our data supports the first 'two-hit' genetic model of FCD and epilepsy that involves dual pathways. We found germline (NPRL3) and somatic (WNT2) contributions from two different genes in functionally related and developmentally important pathways in one brother with FCD. Detection of low frequency somatic second hits is technically challenging but may unravel the molecular architecture of FCDs. References: 1. D'Gama, A.M., et al., Somatic Mutations Activating the mTOR Pathway in Dorsal Telencephalic Progenitors Cause a Continuum of Cortical Dysplasias. Cell Rep., 2017. 21(13): p. 3754-3766. 2. Ribierre, T., et al., Second-hit mosaic mutation in mTORC1 repressor DEPDC5 causes focal cortical dysplasia-associated epilepsy. J Clin Invest., 2018. 128(6): p. 2452-2458. Funding: National Health and Medical Research Council (Grants 1079058 and 1129054; Fellowship 1063799)
Genetics