Electroclinical features of myoclonic-tonic and spasm-tonic seizures in childhood.

Myoclonic-tonic (MT) and spasm-tonic (ST) seizures represent distinctive features in late infantile epileptic encephalopathy (LIEE). This commentary aims to delineate the electroclinical characteristics of MT and ST seizures, setting them apart from other seizure types. Our analysis encompasses 211 ST and MT seizures observed in 31 patients diagnosed with LIEE, providing a comprehensive overview of video-EEG features and polygraphic signatures. In MT seizures, EEG findings reveal a high-voltage diffuse spike/polyspike and wave discharge, often succeeded by diffuse electrodecrements. The amplitude-integrated EEG (aEEG) signature is described as a "reversed checkmark." Conversely, ST seizures exhibit EEG findings such as a vertex positive deflection after a slow-wave and relative electrodecrement, with intermixed epileptiform discharges. In comparison to MT seizures, polygraphic characteristics in ST seizures appear more distinct, featuring a brief rhomboid shape corresponding to the spasm, followed by a lengthier rectangular shape indicative of the tonic phase of the ST seizure. While the pathophysiology of ST and MT seizures remains inadequately understood, their concurrent occurrence and association with other seizure types (tonic, epileptic spasm, myoclonic) within the temporal context of LIEE and other epileptic encephalopathies prompt us to anticipate advancements in our understanding through future research. We hope that this study serves as a foundation for unraveling these complexities in the times to come.

Late infantile epileptic encephalopathy: A distinct developmental and epileptic encephalopathy syndrome.

OBJECTIVE: Within the spectrum of developmental and epileptic encephalopathy (DEE), there are a group of infants with features that are distinct from the well-recognized syndromes of early infantile developmental and epileptic encephalopathy (EIDEE), infantile epileptic spasm syndrome (IESS), and Lennox-Gastaut syndrome (LGS). We refer to this condition as late infantile epileptic encephalopathy (LIEE). Our objective was to highlight the characteristics of this group by analyzing patients who exhibit prototypical features. METHODS: From July 2022 to May 2023, we searched for LIEE features in pediatric patients who underwent epilepsy follow-up at the University of Chicago Comer Children's Hospital. RESULTS: Out of 850 patients evaluated, thirty patients (3.5%) were identified with LIEE based on electroclinical characteristics. These patients had an average onset of epilepsy at 6.8 months and an average onset of LIEE features at 18.1 months. The epilepsy etiology was most commonly genetic and metabolic (50%), followed by congenital cortical malformations (23%), acquired structural abnormalities (20%), and unknown (7%). The predominant seizure types were myoclonic-tonic (70%), spasm-tonic (50%), epileptic spasms (47%), tonic (43%), and myoclonic (43%) seizures. All patients reported a history of either spasm-tonic or myoclonic-tonic seizures in addition to other types. All patients had EEGs showing discontinuity, electrodecrements, or both along with diffuse slowing, background voltages between 100 and 300 µV, and superimposed multifocal, diffuse epileptiform discharges. Every patient, except one, fulfilled the definition of drug-resistant epilepsy, and all reported either moderate-to-severe or severe developmental delay. SIGNIFICANCE: Late infantile epileptic encephalopathy (LIEE) is characterized by several unique clinical and electrographic features. Typically, LIEE manifests in patients during the second year of life and occurs before two years of age, hence late infantile onset. The condition is commonly observed in infants with symptomatic epilepsy. Myoclonic-tonic and spasm-tonic seizures are the quintessential seizure types. The inter-ictal EEG exhibits more organization and lower voltages than seen with hypsarrhythmia and lacks the defining EEG characteristics of EIDEE, IESS, or LGS. We propose that LIEE is a distinct electroclinical syndrome within the spectrum of developmental and epileptic encephalopathies.

Efficacy and tolerability of the modified Atkins diet in children with drug-resistant genetic generalized epilepsy.

OBJECTIVE: The ketogenic diet therapy is a time-tested and potent non-pharmacologic treatment for epilepsy. However, the study of the ketogenic diet in patients with genetic generalized epilepsy (GGE) is not widely established. The aim of this study was to evaluate the efficacy and tolerability of the modified Atkins diet, a variation of the ketogenic diets, as a treatment for drug-resistant GGE. METHODS: A retrospective chart review was performed in patients with epilepsy treated with the modified Atkins diet at the University of Chicago from 2017 to 2020. For three months following diet initiation, participants were monitored for diet tolerability and effect on seizures. Response to the treatment was recorded by self-reporting patients and guardians. RESULTS: Thirteen patients with a diagnosis of drug-resistant GGE were identified. An average of 3.8 anti-seizure medications (ASMs) had been tried and 3.4 years had elapsed from seizure onset before dietary therapy was attempted. Patients were receiving a mean of 2.2 ASMs at the time of diet initiation. After undergoing dietary treatment for three months, 12/13 (92%) patients experienced a greater than 50% reduction in seizure frequency, 6/13 (46%) patients became seizure-free, and 7/13 (54%) were able to discontinue at least one ASM. All patients completed at least three months of dietary therapy with an average duration of 9.3 months at the time of report. One patient reported side effects of fatigue which may be attributed to the diet. SIGNIFICANCE: The modified Atkins diet has shown to be an effective and well-tolerated treatment for children with drug-resistant GGE. The diet provides the additional benefit of aiding to discontinue ASMs and, therefore, minimize the side effects from polypharmacy. Given these results, it seems reasonable to consider the modified Atkins diet as an alternative and possibly earlier treatment option for patients with drug-resistant GGE.

Variants in the SK2 channel gene (KCNN2) lead to dominant neurodevelopmental movement disorders.

KCNN2 encodes the small conductance calcium-activated potassium channel 2 (SK2). Rodent models with spontaneous Kcnn2 mutations show abnormal gait and locomotor activity, tremor and memory deficits, but human disorders related to KCNN2 variants are largely unknown. Using exome sequencing, we identified a de novo KCNN2 frameshift deletion in a patient with learning disabilities, cerebellar ataxia and white matter abnormalities on brain MRI. This discovery prompted us to collect data from nine additional patients with de novo KCNN2 variants (one nonsense, one splice site, six missense variants and one in-frame deletion) and one family with a missense variant inherited from the affected mother. We investigated the functional impact of six selected variants on SK2 channel function using the patch-clamp technique. All variants tested but one, which was reclassified to uncertain significance, led to a loss-of-function of SK2 channels. Patients with KCNN2 variants had motor and language developmental delay, intellectual disability often associated with early-onset movement disorders comprising cerebellar ataxia and/or extrapyramidal symptoms. Altogether, our findings provide evidence that heterozygous variants, likely causing a haploinsufficiency of the KCNN2 gene, lead to novel autosomal dominant neurodevelopmental movement disorders mirroring phenotypes previously described in rodents.