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Epileptic encephalopathies are genetically heterogeneous severe disorders in which epileptic activity contributes to neurological deterioration. We studied two unrelated children presenting with a distinctive early-onset epileptic encephalopathy characterized by refractory epilepsy and absent developmental milestones, as well as thick and short corpus callosum and persistent cavum septum pellucidum on brain MRI. Using whole-exome sequencing, we identified biallelic mutations in seizure threshold 2 (SZT2) in both affected children. The causative mutations include a homozygous nonsense mutation and a nonsense mutation together with an exonic splice-site mutation in a compound-heterozygous state. The latter mutation leads to exon skipping and premature termination of translation, as shown by RT-PCR in blood RNA of the affected boy. Thus, all three mutations are predicted to result in nonsense-mediated mRNA decay and/or premature protein truncation and thereby loss of SZT2 function. Although the molecular role of the peroxisomal protein SZT2 in neuronal excitability and brain development remains to be defined, Szt2 has been shown to influence seizure threshold and epileptogenesis in mice, consistent with our findings in humans. We conclude that mutations in SZT2 cause a severe type of autosomal-recessive infantile encephalopathy with intractable seizures and distinct neuroradiological anomalies.

Summary Purpose:  Benign childhood epilepsy with centrotemporal spikes (BCECTS) is the most common epileptic syndrome in childhood. The outcome is usually excellent, but there are some atypical forms of BCECTS with less favorable outcomes. The aim of this study was to delineate the frequency of these atypical features among patients with BCECTS. Methods:  We conducted a retrospective chart study by retrieving the medical records of all consecutive patients with BCECTS who were evaluated in four pediatric neurology outpatient clinics in Israel between the years 1991 and 2008. Key Findings:  A total of 196 patients with BCECTS were identified (78 female and 118 male; mean age at time of diagnosis 7.64 years, range 1.5–14). The mean duration of follow‐up was 4.43 years (range 2–11). Nine patients (4.6%) developed electrical status epilepticus in slow waves sleep (ESES) during follow‐up, four (2%) had Landau‐Kleffner syndrome, three (1.5%) had BCECTS with frequent refractory seizures, two (1%) had BCECTS with falls at presentation, one (0.5%) had a “classic” atypical variant, and one (0.5%) had oromotor dysfunction. None had rolandic status epilepticus. Sixty‐one patients (31%) had attention deficit hyperactivity disorder (ADHD), 43 (21.9%) had specific cognitive deficits, and 23 (11.7%) had behavioral abnormalities, including aggressiveness, anxiety disorders, depression, and pervasive developmental disorder (PDD). Significance:  The prevalence of most atypical forms of BCECTS other than ESES is low. There is, however, a high prevalence of ADHD and specific cognitive deficits among patients with BCECTS.

The phenotypic spectrum of IQSEC2 disorders includes epilepsy and epileptic encephalopathy. Epileptic encephalopathy is a main clinical feature in sporadic cases. IQSEC2 should be evaluated in both male and female patients with an epileptic encephalopathy.

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