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Searching for mutations associated with Focal Cortical Dysplasia using genomic strategies

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Author(s):
Vanessa Simão de Almeida
Total Authors: 1
Document type: Doctoral Thesis
Press: Campinas, SP.
Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Ciências Médicas
Defense date:
Examining board members:
Íscia Teresinha Lopes Cendes; Cláudia Vianna Maurer Morelli; Clarissa Lin Yasuda; Roger Walz; Marino Muxfeldt Bianchin
Advisor: Íscia Teresinha Lopes Cendes; Fabio Rossi Torres
Abstract

Epilepsies constitute one of the groups of serious neurological diseases that affect 1.5 - 2% of the world population. Several types of malformations of cortical development (MDC) are frequently associated with the occurrence of refractory crises, including Focal Cortical Dysplasia (FCD) which is characterized by cytoarchitectural changes also observed in other MDC, such as Tuberous Sclerosis (TS) and Hemimegaencephaly (HME). A strong association between TS, HME and mosaicism mutations has been demonstrated, and the identification of this type of mutation can contribute to the understanding of these diseases. Therefore, the main goal of this work was to investigate genetic variants related to the etiology of FCD. To this end, Deep Sequencing by NGS was used as a strategy. We sequenced genomic DNA from brain tissue from surgical resection and from peripheral blood of patients with FCD. We performed the sequencing of a customized panel of genes from the mTOR/GATOR pathway and validated it with the digital PCR technique. We found two mosaic variants in brain tissue, located in the MTOR gene (p.Leu1460Pro and p..Ala1459Pro) in two distinct and unrelated patients with FCD type IIb, corresponding to 16.6% of the patients tested (2/12). The percentage of mosaicism in brain tissue was 0.75% and 3.98% respectively in the two patients. Furthermore, to compare the genetic profile of FCD with another MDC, we performed sequencing of the same customized panel on DNA extracted from the blood of 24 patients with the clinical diagnosis of TS, and we found germline mutations in the TSC1 and TSC2 genes in 54.5% of the analyzed patients (12/22), and a potentially pathogenic variant in the IRS1 gene in a single patient. We completed our study of patients with FCD, also researched structural chromosomal alterations (CNVs), used a chromosomal array of molecular cytogenetics and validated by qPCR. We found a CNV with a deletion involving the NOTCH2 gene with pathogenic potential in the same patient that we found a mosaic mutation in the MTOR gene, it may be a case of a two-hit event. Thus, we conclude that 16.6% of patients with FCD have mosaic mutations in brain tissue in genes of the mTOR/GATOR pathway. Thus, we speculate that if mosaic mutations are indeed a frequent cause of FCD, it is possible that other pathways are involved, in addition to the mTOR/GATOR pathway investigated in this work. We found germline mutations predominantly in the TSC1 and TSC2 genes in most patients with TS, which would indicate a genetic etiology in these patients fundamentally different from that found in patients with FCD. When we found chromosomal structural alterations in a patient with FCD, we showed the importance of investigating this type of mutation in these patients. Thus, we conclude that our work contributed to a better understanding of the genetic etiology of FCDs (AU)

FAPESP's process: 15/19768-1 - Searching for mutations associated with focal cortical dysplasia using genomic strategies
Grantee:Vanessa Simão de Almeida
Support type: Scholarships in Brazil - Doctorate