Adaptive behavior and psychiatric comorbidities in KCNB1 encephalopathy

Investigating Quality of Life and Adaptive Functioning in Patients With SCN8A-Related Epilepsy

SCN8A-related epilepsy is associated with a spectrum of seizure and neurodevelopmental phenotypes; however, there is limited information regarding nonseizure outcomes. We performed a cross-sectional study investigating quality of life (QoL) and adaptive functioning in this population utilizing the Quality of Life Inventory-Disability (QI-Disability) survey and Vineland Adaptive Behavior Scales (VABS). Nineteen patients with SCN8A pathogenic variants were included. There was a significant difference in QI-Disability and VABS scores between clinical epilepsy phenotypes. Greater seizure frequency and number of antiseizure medications were both associated with lower VABS and QI-Disability total scores, but number of antiseizure medications was associated with more QoL domains than seizure frequency. QI-Disability scores were positively associated with adaptive functioning except for the QoL domain of Negative Emotions. This study is the first to characterize the spectrum of QoL and adaptive functioning in the SCN8A-related disorder population and investigate their relationships to each other and to seizure outcomes. Both the QI-Disability and VABS show promise as potential clinical outcome assessments in future SCN8A-related disorder cohorts.

Gain-of-function enhancer variant near KCNB1 causes familial ST-depression syndrome

BACKGROUND AND AIMS

Familial ST-depression syndrome (FSTD) is a recently identified inherited cardiac disease associated with arrhythmias and systolic dysfunction. The underlying genetic aetiology has remained elusive. This study aimed at finding the causative variant.

METHODS

A total of 67 FSTD patients (20 families) were studied. Linkage analysis and whole-genome sequencing (WGS) were initially performed. An identified non-coding variant was functionally characterized in AC16 human cardiomyocytes, muscle tissue, and human myocardium. In silico analyses, luciferase and dCas9-activator/repressor assays, protein-DNA experiments, chromosome conformation capture (4C), and RNA sequencing were also performed.

RESULTS

The electrocardiographic (ECG) phenotype was inherited in an autosomal dominant manner in all families. Linkage analysis revealed a single peak on chromosome 20, and WGS identified a single, rare, non-coding variant located 18 kb downstream of KCNB1 on chromosome 20 in all affected individuals. Perfect co-segregation with the ECG phenotype was observed together with full penetrance in all families. The variant creates a MEF2-binding site and presence of the variant allele or MEF2 co-expression enhanced transcriptional activity. dCas9-activator/repressor assays showed that KCNB1 was the only gene consistently regulated by the locus and 4C experiments in AC16 cells and human muscle tissue confirmed the locus-KCNB1 promoter interaction. Expression analysis in human endocardial tissue did not document any change in gene expression likely explained by expressional heterogeneity.

CONCLUSIONS

A gain-of-function enhancer variant creates a hyperactive regulatory locus that interacts with the KCNB1 promoter and causes FSTD. This is the first time that KCNB1 has been implicated in human cardiac electrophysiology and arrhythmogenesis.

De novo KCNB1 missense variant causing developmental and epileptic encephalopathy: Two case reports

RATIONALE

Developmental and epileptic encephalopathy (DEE) defines a group of severe and heterogeneous neurodevelopmental disorders. The voltage-gated potassium channel subfamily 2 voltage-gated potassium channel α subunit encoded by the KCNB1 gene is essential for neuronal excitability. Previous studies have shown that KCNB1 variants can cause DEE. Herein, we report the cases of 2 children with DEE caused by pathogenic variants in the KCNB1 gene. Trio whole-exome sequencing identified novel KCNB1 genotypes, c. 1160C > A and c.1012C > T, which had not been reported previously, in 2 unrelated patients.

PATIENT CONCERNS

Two children were admitted to our hospital for a detailed evaluation of frequent seizures. And both of these children have abnormal electroencephalogram and brain magnetic resonance imaging results, accompanied by developmental delay.

DIAGNOSES

A genetic study using trio-whole-exome sequencing confirmed the diagnosis of KCNB1-related developmental and epileptic encephalopathy.

INTERVENTIONS

Both patients accepted the treatment of antiepileptic drugs. 1 patient had seizure remission with a combination of sodium valproate and lamotrigine, and the other was lost to follow-up.

OUTCOMES

Trio-whole-exome sequencing technology was used to determine the etiology of the 2 children with DEE.

LESSONS

This study confirmed that genetic testing provides a basis for the diagnosis of children with abnormal electroencephalogram and brain magnetic resonance imaging findings and developmental delay, and provides data supporting a future phenotype-genotype correlation study.

Adaptive behaviour in adolescents and adults with Dravet syndrome

AIM

To explore the feasibility of using an adaptive behaviour profile (ABP) assessment generated from a well-known measure-the Vineland Adaptive Behavior Scales, Second Edition (VABS-II)-as an instrument for outcome measures in adolescents and adults with Dravet syndrome.

METHOD

We administered the VABS-II to 35 adolescents and adults with Dravet syndrome (15 males; mean age 24 years, SD 8 years, range: 12-46 years) and collected epilepsy history and neurological features at the time of assessment. We conducted a cross-sectional analysis of VABS-II raw scores and performed cluster analysis to identify different subgroups. We then explored possible relationships between clinical and epilepsy features, ABPs, and age.

RESULTS

Most participants obtained the minimum standard scores in the various VABS-II subdomains, while the raw score analysis outlined interindividual and intraindividual differences among skills. We found two subpopulations: one with a 'lower' ABP and one with a 'higher' ABP, corresponding respectively to individuals in whom myoclonic seizures or generalized spike-and-wave activity were present ('complete phenotype') or absent ('incomplete phenotype') on electroencephalography.

INTERPRETATION

This study further delineates the natural history of Dravet syndrome. The assessment of an ABP through the VABS-II raw score analysis provides a means by which to illustrate profiles of adaptive behaviour in adolescents and adults with Dravet syndrome but shows limitations related to poor sensitivity in measuring fine clinical details. There is a need for new and more specific tools to monitor patients with developmental and epileptic encephalopathies.

The association between gene polymorphisms in voltage-gated potassium channels Kv2.1 and Kv4.2 and susceptibility to autism spectrum disorder

BACKGROUND

Autism spectrum disorder (ASD) is a heritable form of neurodevelopmental disorder that arises through synaptic dysfunction. Given the involvement of voltage-gated potassium (Kv) channels in the regulation of synaptic plasticity, we aimed to explore the relationship between the genetic variants in the KCNB1 and KCND2 genes (encoding Kv2.1 and Kv4.2, respectively) and the risk of developing ASD.

METHODS

A total of 243 patients with ASD and 243 healthy controls were included in the present study. Sixty single nucleotide polymorphisms (SNPs) (35 in KCNB1 and 25 in KCND2) were genotyped using the Sequenom Mass Array.

RESULTS

There were no significant differences in the distribution of allele frequencies and genotype frequencies in KCNB1 between cases and controls. However, the differences were significant in the allelic distribution of KCND2 rs1990429 (p _Bonferroni < 0.005) and rs7793864 (p _Bonferroni < 0.005) between the two groups. KCND2 rs7800545 (p _FDR = 0.045) in the dominant model and rs1990429 (p _FDR < 0.001) and rs7793864 (p _FDR < 0.001) in the over-dominant model were associated with ASD risk. The G/A genotype of rs1990429 in the over-dominant model and the G/A-G/G genotype of rs7800545 in the dominant model were correlated with lower severity in the Autism Diagnostic Interview-Revised (ADI-R) restricted repetitive behavior (RRB) domain.

CONCLUSION

Our results provide evidence that KCND2 gene polymorphism is strongly associated with ASD susceptibility and the severity of RRB.