Abstract
Objective To alert about the wide margin of unpredictability that distribution of somatic MTOR mosaicism may have in the brain and the risk for independent epileptogenesis arising from the seemingly healthy contralateral hemisphere after complete removal of epileptogenic focal cortical dysplasia (FCD).
Methods Clinical, EEG, MRI, histopathology, and molecular genetics in 2 patients (1 and 2) treated with focal resections and subsequent complete hemispherectomy for epileptogenic FCD due to somatic MTOR mutations. Autoptic brain study of bilateral asymmetric hemispheric dysplasia and identification of alternative allele fraction (AAF) rates for AKT1 (patient 3).
Results The strongly hyperactivating p.Ser2215Phe (patient 1) and p.Leu1460Pro (patient 2) MTOR mutations were at low-level AAF in the dysplastic tissue. After repeated resections and eventual complete hemispherectomy, both patients manifested intractable seizures arising from the contralateral, seemingly healthy hemisphere. In patient 3, the p.Glu17Lys AKT1 mutation exhibited random distribution and AAF rates in different tissues with double levels in the more severely dysplastic cerebral hemisphere.
Conclusions Our understanding of the distribution of somatic mutations in the brain in relation to the type of malformation and its hypothesized time of origin may be faulty. Large studies may reveal that the risk of a first surgery being disappointing might be related more to the specific somatic mammalian target of rapamycin mutation identified than to completeness of resection and that the advantages of repeated resections after a first unsuccessful operation should be weighed against the risk of the contralateral hemisphere becoming in turn epileptogenic.
Glossary
- AAF=
- alternative allele fraction;
- AED=
- antiepileptic drug;
- DMEG=
- dysplastic megalencephaly;
- FCDII=
- focal cortical dysplasia type II;
- HME=
- hemimegalencephaly;
- MCD=
- malformations of cortical development;
- MEG=
- megalencephaly;
- mTOR=
- mammalian target of rapamycin;
- OFC=
- occipital frontal circumference (head circumference);
- smMIP=
- single-molecule molecular inversion probe;
- WES=
- whole-exome sequencing
Footnotes
Go to Neurology.org/NG for full disclosures. Funding information is provided at the end of the article.
The Article Processing Charge was funded by the University of Florence.
- Received May 24, 2020.
- Accepted in final form October 21, 2020.
- Copyright © 2020 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American Academy of Neurology.
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