Dataset Information

Germline and somatic mutations in the MTOR gene in focal cortical dysplasia and epilepsy.

ABSTRACT:

Objective

To assess the prevalence of somatic MTOR mutations in focal cortical dysplasia (FCD) and of germline MTOR mutations in a broad range of epilepsies.

Methods

We collected 20 blood-brain paired samples from patients with FCD and searched for somatic variants using deep-targeted gene panel sequencing. Germline mutations in MTOR were assessed in a French research cohort of 93 probands with focal epilepsies and in a diagnostic Danish cohort of 245 patients with a broad range of epilepsies. Data sharing among collaborators allowed us to ascertain additional germline variants in MTOR.

Results

We detected recurrent somatic variants (p.Ser2215Phe, p.Ser2215Tyr, and p.Leu1460Pro) in the MTOR gene in 37% of participants with FCD II and showed histologic evidence for activation of the mTORC1 signaling cascade in brain tissue. We further identified 5 novel de novo germline missense MTOR variants in 6 individuals with a variable phenotype from focal, and less frequently generalized, epilepsies without brain malformations, to macrocephaly, with or without moderate intellectual disability. In addition, an inherited variant was found in a mother-daughter pair with nonlesional autosomal dominant nocturnal frontal lobe epilepsy.

Conclusions

Our data illustrate the increasingly important role of somatic mutations of the MTOR gene in FCD and germline mutations in the pathogenesis of focal epilepsy syndromes with and without brain malformation or macrocephaly.

SUBMITTER: Moller RS

PROVIDER: S-EPMC5089441 | biostudies-literature | 2016 Dec

REPOSITORIES: biostudies-literature

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Publications

Germline and somatic mutations in the <i>MTOR</i> gene in focal cortical dysplasia and epilepsy.

Møller Rikke S RS Weckhuysen Sarah S Chipaux Mathilde M Marsan Elise E Taly Valerie V Bebin E Martina EM Hiatt Susan M SM Prokop Jeremy W JW Bowling Kevin M KM Mei Davide D Conti Valerio V de la Grange Pierre P Ferrand-Sorbets Sarah S Dorfmüller Georg G Lambrecq Virginie V Larsen Line H G LH Leguern Eric E Guerrini Renzo R Rubboli Guido G Cooper Gregory M GM Baulac Stéphanie S

Neurology. Genetics 20161031 6

<h4>Objective</h4>To assess the prevalence of somatic <i>MTOR</i> mutations in focal cortical dysplasia (FCD) and of germline <i>MTOR</i> mutations in a broad range of epilepsies.<h4>Methods</h4>We collected 20 blood-brain paired samples from patients with FCD and searched for somatic variants using deep-targeted gene panel sequencing. Germline mutations in <i>MTOR</i> were assessed in a French research cohort of 93 probands with focal epilepsies and in a diagnostic Danish cohort of 245 patients ...[more]

PMID: 27830187

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Project description:ImportanceFocal cortical dysplasia (FCD), hemimegalencephaly, and megalencephaly constitute a spectrum of malformations of cortical development with shared neuropathologic features. These disorders are associated with significant childhood morbidity and mortality.ObjectiveTo identify the underlying molecular cause of FCD, hemimegalencephaly, and diffuse megalencephaly.Design, setting, and participantsPatients with FCD, hemimegalencephaly, or megalencephaly (mean age, 11.7 years; range, 2-32 years) were recruited from Pediatric Hospital A. Meyer, the University of Hong Kong, and Seattle Children's Research Institute from June 2012 to June 2014. Whole-exome sequencing (WES) was performed on 8 children with FCD or hemimegalencephaly using standard-depth (50-60X) sequencing in peripheral samples (blood, saliva, or skin) from the affected child and their parents and deep (150-180X) sequencing in affected brain tissue. Targeted sequencing and WES were used to screen 93 children with molecularly unexplained diffuse or focal brain overgrowth. Histopathologic and functional assays of phosphatidylinositol 3-kinase-AKT (serine/threonine kinase)-mammalian target of rapamycin (mTOR) pathway activity in resected brain tissue and cultured neurons were performed to validate mutations.Main outcomes and measuresWhole-exome sequencing and targeted sequencing identified variants associated with this spectrum of developmental brain disorders.ResultsLow-level mosaic mutations of MTOR were identified in brain tissue in 4 children with FCD type 2a with alternative allele fractions ranging from 0.012 to 0.086. Intermediate-level mosaic mutation of MTOR (p.Thr1977Ile) was also identified in 3 unrelated children with diffuse megalencephaly and pigmentary mosaicism in skin. Finally, a constitutional de novo mutation of MTOR (p.Glu1799Lys) was identified in 3 unrelated children with diffuse megalencephaly and intellectual disability. Molecular and functional analysis in 2 children with FCD2a from whom multiple affected brain tissue samples were available revealed a mutation gradient with an epicenter in the most epileptogenic area. When expressed in cultured neurons, all MTOR mutations identified here drive constitutive activation of mTOR complex 1 and enlarged neuronal size.Conclusions and relevanceIn this study, mutations of MTOR were associated with a spectrum of brain overgrowth phenotypes extending from FCD type 2a to diffuse megalencephaly, distinguished by different mutations and levels of mosaicism. These mutations may be sufficient to cause cellular hypertrophy in cultured neurons and may provide a demonstration of the pattern of mosaicism in brain and substantiate the link between mosaic mutations of MTOR and pigmentary mosaicism in skin.

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