Identification of a mosaic MTOR variant in purified neuronal DNA in a patient with focal cortical dysplasia using a novel depth electrode harvesting technique.

OBJECTIVE: Recent studies have identified brain somatic variants as a cause of focal epilepsy. These studies relied on resected tissue from epilepsy surgery, which is not available in most patients. The use of trace tissue adherent to depth electrodes used for stereo electroencephalography (EEG) has been proposed as an alternative but is hampered by the low cell quality and contamination by nonbrain cells. Here, we use our improved depth electrode harvesting technique that purifies neuronal nuclei to achieve molecular diagnosis in a patient with focal cortical dysplasia (FCD). METHODS: Depth electrode tips were collected, pooled by brain region and seizure onset zone, and nuclei were isolated and sorted using fluorescence-activated nuclei sorting (FANS). Somatic DNA was amplified from neuronal and astrocyte nuclei using primary template amplification followed by exome sequencing of neuronal DNA from the affected pool, unaffected pool, and saliva. The identified variant was validated using droplet digital polymerase chain reaction (PCR). RESULTS: An 11-year-old male with drug-resistant genetic-structural epilepsy due to left anterior insula FCD had seizures from age 3 years. Stereo EEG confirmed seizure onset in the left anterior insula. The two anterior insula electrodes were combined as the affected pool and three frontal electrodes as the unaffected pool. FANS isolated 140 neuronal nuclei from the affected and 245 neuronal nuclei from the unaffected pool. A novel somatic missense MTOR variant (p.Leu489Met, CADD score 23.7) was identified in the affected neuronal sample. Droplet digital PCR confirmed a mosaic gradient (variant allele frequency = .78% in affected neuronal sample; variant was absent in all other samples). SIGNIFICANCE: Our findings confirm that harvesting neuronal DNA from depth electrodes followed by molecular analysis to identify brain somatic variants is feasible. Our novel method represents a significant improvement compared to the previous method by focusing the analysis on high-quality cells of the cell type of interest.

Hydranencephaly: Clinical Features and Survivorship in a Retrospective Cohort.

OBJECTIVE: Hydranencephaly is a congenital central nervous system disorder characterized by the complete or near-complete absence of the cerebral cortex and basal ganglia. Because of its rarity, data on the clinical features and survivorship remain sparse. We aim to determine the clinical features and survivorship of a cohort of patients with hydranencephaly. METHODS: We performed a retrospective cohort study of all patients diagnosed with hydranencephaly at our institution from 2008 to 2018. Data on demographics, clinical features, presence of comorbidities, surgical operations performed, and status on last follow-up were collected. Survival curves were generated using Kaplan-Meier analysis. RESULTS: Fifty patients were included in the cohort, who had a median age at diagnosis of 4 months and a female predilection. The most common clinical manifestations were macrocephaly (92%) and seizures or myoclonic movements. Infection was present in 36% of cases, endocrinopathies in 22%, dysmorphisms in 20%, and cardiac disease in 8%. Twenty patients underwent shunt insertion, with half developing a postoperative complication at a mean follow-up of 14.9 months. The median survival of the cohort was not reached at 7.5 years. Among the patients with follow-up, characteristics were similar between the surgical and nonsurgical groups, except for the greater incidence of infections in the nonsurgical group. The survival curves among the groups were significantly different, with a hazard ratio of 3.731 in the nonsurgical group. CONCLUSIONS: In this large single-center retrospective cohort of patients with hydranencephaly, novel findings are presented regarding the clinical manifestations and survivorship of this condition.