Brain somatic mutations in MTOR reveal translational dysregulations underlying intractable focal epilepsy.

Brain somatic mutations confer genomic diversity in the human brain and cause neurodevelopmental disorders. Recently, brain somatic activating mutations in MTOR have been identified as a major etiology of intractable epilepsy in patients with cortical malformations. However, the molecular genetic mechanism of how brain somatic mutations in MTOR cause intractable epilepsy has remained elusive. In this study, translational profiling of intractable epilepsy mouse models with brain somatic mutations and genome-edited cells revealed a novel translational dysregulation mechanism and mTOR activation-sensitive targets mediated by human MTOR mutations that lead to intractable epilepsy with cortical malformation. These mTOR targets were found to be regulated by novel mTOR-responsive 5'-UTR motifs, distinct from known mTOR inhibition-sensitive targets regulated by 5' terminal oligopyrimidine motifs. Novel mTOR target genes were validated in patient brain tissues, and the mTOR downstream effector eIF4E was identified as a new therapeutic target in intractable epilepsy via pharmacological or genetic inhibition. We show that metformin, an FDA-approved eIF4E inhibitor, suppresses intractable epilepsy. Altogether, the present study describes translational dysregulation resulting from brain somatic mutations in MTOR, as well as the pathogenesis and potential therapeutic targets of intractable epilepsy.

Focal neuronal migration disorders and intractable partial epilepsy: a study of 30 patients.

We studied 30 patients with partial epilepsy and a radiological or pathological diagnosis of localized neuronal migration disorders, with a view to surgical treatment. Eight patients had identifiable prenatal etiological factors. The frequency of complex partial, partial motor, and secondarily generalized seizures was approximately 70% each. Drop attacks were present in 27%: Their presence usually correlated with a lesion involving the central region. Partial motor or generalized convulsive status epilepticus occurred in 30%, and was most frequently associated with extensive structural abnormalities involving two or more lobes. A full-scale intelligence quotient of less than 80 was found in 44%. Magnetic resonance imaging (MRI) was superior to computed tomography for identification of the dysplastic cortical lesions. In one third, MRI showed only subcortical abnormalities. It did not allow distinction between true pachygyria, focal cortical dysplasia, or the forme fruste of tuberous sclerosis. The epileptogenic area was usually more extensive than the lesion; it was multilobar in more than 70% of patients. Of 26 surgically treated patients, a histological diagnosis of the type of neuronal migration disorder was possible in 22: 12 had focal cortical dysplasia and 10 the forme fruste of tuberous sclerosis. In the remaining 4, no definite histological diagnosis was made, since the maximally abnormal tissue could not be examined. In the latter, and in the 4 nonoperated patients, the diagnosis of neuronal migration disorder was based on imaging findings. The presence of the forme fruste of tuberous sclerosis correlated with delayed psychomotor development and more extensive epileptogenic areas.

Focal neuronal migration disorders and intractable partial epilepsy: results of surgical treatment.

Twenty-six patients with focal or lateralized neuronal migration disorders and intractable partial epilepsy were treated surgically. Twenty-four had reliable follow-up ranging from 1 to 15 years (mean, 5.0). Pathologically, they fell into two categories: focal cortical dysplasia (12 patients) and forme fruste of tuberous sclerosis (8 patients). In the remaining 4 patients, the material was inadequate for histological analysis. Outcome regarding seizure control was assessed according to a classification most sensitive to variations in frequency of major attacks. Ten (42%) of the 24 patients achieved good or excellent outcome, 6 (25%) had a worthwhile decrease in seizure frequency, and 8 (33%) had only discrete improvement. The variable most strongly correlated with surgical outcome was the amount of lesion removed. Seventy-seven percent of patients in whom a complete excision or excision of 50% or more of the lesion was accomplished achieved excellent or good surgical outcome. Conversely, no patient with less than 50% of the lesion removed attained the same result. There was no correlation between other clinical, radiological, or electrographic variables and outcome regarding seizure control. Specifically there was no significant correlation between the amount of excision of the epileptogenic area as judged by scalp electroencephalography and electrocorticography studies, and surgical outcome. In patients with neuronal migration disorders and intractable partial epilepsy, removal of the structural abnormality takes precedence over removal of epileptogenic tissue as the main surgical strategy to achieve seizure control.