SCN2A Pathogenic Variants and Epilepsy: Heterogeneous Clinical, Genetic and Diagnostic Features

Frequency of SCN2A-related disorder in the regional epilepsy centre of brescia between 2002 and 2021

OBJECTIVE

SCN2A gene pathogenic variants are associated with a wide phenotypic spectrum, encompassing epilepsy, developmental delay, and autism spectrum disorder. Researches conducted in Denmark have revealed a disease frequency of approximately 1/78,608 (0.0012%) live births in this population. We estimated the frequency of SCN2A-related disorder in the birth cohort of Brescia and its province between 2002 and 2021.

METHODS

Frequency was calculated by ratio between patients with SCN2A pathogenic variant and the total number of live births at the Regional Epilepsy Center of Brescia, between 2002 and 2021. The number of births in Brescia and province was obtained from the Italian National Institute of Statistics (ISTAT).

RESULTS

A frequency of 11/23,2678 births (0.0047%) was found. In comparison with Danish data, we noticed a higher frequency of the pathogenic variant in our population, even considering the same time frame (0.0035% of subjects born between 2006 and 2014).

CONCLUSION

The frequency of SCN2A pathogenic variant among live births in Brescia and its Province between 2006 and 2014 was about three times that of Danish population; this difference was about four times if we consider the period from 2002 to 2021. More studies are needed to further delineate the frequency of SCN2A pathogenic variant in Italian population.

Human iPSC-derived microglia sense and dampen hyperexcitability of cortical neurons carrying the epilepsy-associated SCN2A-L1342P mutation

Neuronal hyperexcitability is a hallmark of seizures. It has been recently shown in rodent models of seizures that microglia, the brain's resident immune cells, can respond to and modulate neuronal excitability. However, how human microglia interacts with human neurons to regulate hyperexcitability mediated by epilepsy-causing genetic mutation found in human patients remains unknown. The SCN2A genetic locus is responsible for encoding the voltage-gated sodium channel Nav1.2, recognized as one of the leading contributors to monogenic epilepsies. Previously, we demonstrated that the recurring Nav1.2-L1342P mutation identified in patients with epilepsy leads to hyperexcitability in a hiPSC-derived cortical neuron model from a male donor. While microglia play an important role in the brain, these cells originate from a different lineage (yolk sac) and thus are not naturally present in hiPSCs-derived neuronal culture. To study how microglia respond to diseased neurons and influence neuronal excitability, we established a co-culture model comprising hiPSC-derived neurons and microglia. We found that microglia display altered morphology with increased branch length and enhanced calcium signal when co-cultured with neurons carrying the Nav1.2-L1342P mutation. Moreover, the presence of microglia significantly lowers the action potential firing of neurons carrying the mutation. Interestingly, we further demonstrated that the current density of sodium channels in neurons carrying the epilepsy-associated mutation was reduced in the presence of microglia. Taken together, our work reveals a critical role of human iPSCs-derived microglia in sensing and dampening hyperexcitability mediated by an epilepsy-causing mutation present in human neurons, highlighting the importance of neuron-microglia interactions in human pathophysiology.

SCN2A-Related Epilepsy: The Phenotypic Spectrum, Treatment and Prognosis

OBJECTIVE

The aim of this study was to analyze the phenotypic spectrum, treatment, and prognosis of 72 Chinese children with SCN2A variants.

METHODS

The SCN2A variants were detected by next-generation sequencing. All patients were followed up at a pediatric neurology clinic in our hospital or by telephone.

RESULTS

In 72 patients with SCN2A variants, the seizure onset age ranged from the first day of life to 2 years and 6 months. The epilepsy phenotypes included febrile seizures (plus) (n = 2), benign (familial) infantile epilepsy (n = 9), benign familial neonatal-infantile epilepsy (n = 3), benign neonatal epilepsy (n = 1), West syndrome (n = 16), Ohtahara syndrome (n = 15), epilepsy of infancy with migrating focal seizures (n = 2), Dravet syndrome (n = 1), early infantile epileptic encephalopathy (n = 15), and unclassifiable developmental and epileptic encephalopathy (n = 8). Approximately 79.2% (57/72) patients had varying degrees of developmental delay. All patients had abnormal MRI findings with developmental delay. 91.7% (55/60) patients with de novo SCN2A variants had development delay, while only 16.7% (2/12) patients with inherited SCN2A variants had abnormal development. 83.9% (26/31) SCN2A variants that were located in transmembrane regions of the protein were detected in patients with development delay. Approximately 69.2% (9/13) SCN2A variants detected in patients with normal development were located in the non-transmembrane regions. Approximately 54.2% (39/72) patients were seizure-free at a median age of 8 months. Oxcarbazepine has been used by 38 patients, and seizure-free was observed in 11 of them (11/38, 28.9%), while 6 patients had seizure worsening by oxcarbazepine. All 3 patients used oxcarbazepine and with seizure onset age > 1 year presented seizure exacerbation after taking oxcarbazepine. Valproate has been used by 53 patients, seizure-free was observed in 22.6% (12/53) of them.

CONCLUSION

The phenotypic spectrum of SCN2A-related epilepsy was broad, ranging from benign epilepsy in neonate and infancy to severe epileptic encephalopathy. Oxcarbazepine and valproate were the most effective drugs in epilepsy patients with SCN2A variants. Sodium channel blockers often worsen seizures in patients with seizure onset beyond 1 year of age. Abnormal brain MRI findings and de novo variations were often related to poor prognosis. Most SCN2A variants located in transmembrane regions were related to patients with developmental delay.