Generalized Epilepsy and Myoclonic Seizures in 22q11.2 Deletion Syndrome

Genome-wide identification and phenotypic characterization of seizure-associated copy number variations in 741,075 individuals

Copy number variants (CNV) are established risk factors for neurodevelopmental disorders with seizures or epilepsy. With the hypothesis that seizure disorders share genetic risk factors, we pooled CNV data from 10,590 individuals with seizure disorders, 16,109 individuals with clinically validated epilepsy, and 492,324 population controls and identified 25 genome-wide significant loci, 22 of which are novel for seizure disorders, such as deletions at 1p36.33, 1q44, 2p21-p16.3, 3q29, 8p23.3-p23.2, 9p24.3, 10q26.3, 15q11.2, 15q12-q13.1, 16p12.2, 17q21.31, duplications at 2q13, 9q34.3, 16p13.3, 17q12, 19p13.3, 20q13.33, and reciprocal CNVs at 16p11.2, and 22q11.21. Using genetic data from additional 248,751 individuals with 23 neuropsychiatric phenotypes, we explored the pleiotropy of these 25 loci. Finally, in a subset of individuals with epilepsy and detailed clinical data available, we performed phenome-wide association analyses between individual CNVs and clinical annotations categorized through the Human Phenotype Ontology (HPO). For six CNVs, we identified 19 significant associations with specific HPO terms and generated, for all CNVs, phenotype signatures across 17 clinical categories relevant for epileptologists. This is the most comprehensive investigation of CNVs in epilepsy and related seizure disorders, with potential implications for clinical practice.

The CLDN5 gene at the blood-brain barrier in health and disease

The CLDN5 gene encodes claudin-5 (CLDN-5) that is expressed in endothelial cells and forms tight junctions which limit the passive diffusions of ions and solutes. The blood-brain barrier (BBB), composed of brain microvascular endothelial cells and associated pericytes and end-feet of astrocytes, is a physical and biological barrier to maintain the brain microenvironment. The expression of CLDN-5 is tightly regulated in the BBB by other junctional proteins in endothelial cells and by supports from pericytes and astrocytes. The most recent literature clearly shows a compromised BBB with a decline in CLDN-5 expression increasing the risks of developing neuropsychiatric disorders, epilepsy, brain calcification and dementia. The purpose of this review is to summarize the known diseases associated with CLDN-5 expression and function. In the first part of this review, we highlight the recent understanding of how other junctional proteins as well as pericytes and astrocytes maintain CLDN-5 expression in brain endothelial cells. We detail some drugs that can enhance these supports and are being developed or currently in use to treat diseases associated with CLDN-5 decline. We then summarise mutagenesis-based studies which have facilitated a better understanding of the physiological role of the CLDN-5 protein at the BBB and have demonstrated the functional consequences of a recently identified pathogenic CLDN-5 missense mutation from patients with alternating hemiplegia of childhood. This mutation is the first gain-of-function mutation identified in the CLDN gene family with all others representing loss-of-function mutations resulting in mis-localization of CLDN protein and/or attenuated barrier function. Finally, we summarize recent reports about the dosage-dependent effect of CLDN-5 expression on the development of neurological diseases in mice and discuss what cellular supports for CLDN-5 regulation are compromised in the BBB in human diseases.

Df(h22q11)/+ mouse model exhibits reduced binding levels of GABAA receptors and structural and functional dysregulation in the inhibitory and excitatory networks of hippocampus

The 22q11.2 hemizygous deletion confers high risk for multiple neurodevelopmental disorders. Inhibitory signaling, largely regulated through GABA_A receptors, is suggested to serve a multitude of brain functions that are disrupted in the 22q11.2 deletion syndrome. We investigated the putative deficit of GABA_A receptors and the potential substrates contributing to the inhibitory and excitatory dysregulations in hippocampal networks of the Df(h22q11)/+ mouse model of the 22q11.2 hemizygous deletion. The Df(h22q11)/+ mice exhibited impairments in several hippocampus-related functional domains, represented by impaired spatial memory and sensory gating functions. Autoradiography using the [³H]muscimol tracer revealed a significant reduction in GABA_A receptor binding in the CA1 and CA3 subregions, together with a loss of GAD67⁺ interneurons in CA1 of Df(h22q11)/+ mice. Furthermore, electrophysiology recordings exhibited significantly higher neuronal activity in CA3, in response to the GABA_A receptor antagonist, bicuculline, as compared with wild type mice. Density and volume of dendritic spines in pyramidal neurons were reduced and Sholl analysis also showed a reduction in the complexity of basal dendritic tree in CA1 and CA3 subregions of Df(h22q11)/+ mice. Overall, our findings demonstrate that hemizygous deletion in the 22q11.2 locus leads to dysregulations in the inhibitory circuits, involving reduced binding levels of GABA_A receptors, in addition to functional and structural modulations of the excitatory networks of hippocampus.

Role of circulating miR 194-5p, miR 106b, and miR 146a as potential biomarkers for epilepsy: a case-control study

Background

Epilepsy is a chronic neurological disease. A suitable biomarker for epilepsy diagnosis remains lacking. MicroRNAs (miRNAs) were pronounced as promising biomarkers for epileptogenesis.

Objectives

To analyze the expression levels of miR 194-5p, miR 106b, and miR 146a in Egyptian epileptic patients compared to control subjects and to detect their correlation to clinical characteristics.

Subjects and methods

We evaluated the expression levels of miR 106b, miR 146a, and miR 194-5p using real-time quantitative polymerase chain reaction (qRT-PCR) in 50 subjects: 15 patients with idiopathic generalized epilepsy, 15 patients with focal epilepsy (3 idiopathic and 12 cryptogenic), and 20 healthy controls.

Results

miR 106b and miR 194-5p were upregulated in the generalized epilepsy group compared to control; miR 194-5p was significantly downregulated in the focal epilepsy group compared to the generalized epilepsy group and control (p ˂ 0.05). miR 194-5p was negatively correlated to disease duration in patients with focal epilepsy; the three microRNAs were positively correlated to each other (p ˂ 0.05).

Conclusion

Serum miR 194-5P and miR 106b can be used as potential non-invasive biomarkers in the evaluation of idiopathic generalized epilepsy.

Genetic Landscape of Common Epilepsies: Advancing towards Precision in Treatment

Epilepsy, a neurological disease characterized by recurrent seizures, is highly heterogeneous in nature. Based on the prevalence, epilepsy is classified into two types: common and rare epilepsies. Common epilepsies affecting nearly 95% people with epilepsy, comprise generalized epilepsy which encompass idiopathic generalized epilepsy like childhood absence epilepsy, juvenile myoclonic epilepsy, juvenile absence epilepsy and epilepsy with generalized tonic-clonic seizure on awakening and focal epilepsy like temporal lobe epilepsy and cryptogenic focal epilepsy. In 70% of the epilepsy cases, genetic factors are responsible either as single genetic variant in rare epilepsies or multiple genetic variants acting along with different environmental factors as in common epilepsies. Genetic testing and precision treatment have been developed for a few rare epilepsies and is lacking for common epilepsies due to their complex nature of inheritance. Precision medicine for common epilepsies require a panoramic approach that incorporates polygenic background and other non-genetic factors like microbiome, diet, age at disease onset, optimal time for treatment and other lifestyle factors which influence seizure threshold. This review aims to comprehensively present a state-of-art review of all the genes and their genetic variants that are associated with all common epilepsy subtypes. It also encompasses the basis of these genes in the epileptogenesis. Here, we discussed the current status of the common epilepsy genetics and address the clinical application so far on evidence-based markers in prognosis, diagnosis, and treatment management. In addition, we assessed the diagnostic predictability of a few genetic markers used for disease risk prediction in individuals. A combination of deeper endo-phenotyping including pharmaco-response data, electro-clinical imaging, and other clinical measurements along with genetics may be used to diagnose common epilepsies and this marks a step ahead in precision medicine in common epilepsies management.

Myoclonic epilepsy, parkinsonism, schizophrenia and left-handedness as common neuropsychiatric features in 22q11.2 deletion syndrome

BACKGROUND

22q11.2 deletion syndrome (22q11.2DS) is considered as the genetic model of schizophrenia. However, its polymorphic nature has led researchers to further investigate its neuropsychiatric manifestations.

METHODS

We enrolled 56 adults (38 men, 18 women) diagnosed with 22q11.2DS. All subjects were evaluated by a multidisciplinary team. The neuropsychiatric features were investigated by means of clinical and neurophysiological evaluation (video-EEG).

RESULTS

Thirty per cent of our patients were left-handed. Fifty-eight per cent had a low IQ, and 22 of 56 subjects had psychotic disorders (13 of 22 with schizophrenia). Eighteen patients reported at least one seizure in their lifetime, and ten were diagnosed with epilepsy; among them, seven had genetic generalised epilepsy (GGE), and five of seven showed features suggestive of juvenile myoclonic epilepsy (JME). Video-EEG recordings revealed generalised epileptiform abnormalities in 24 of 56 cases. Besides, only one patient with epilepsy had a cardiac malformation. Lastly, 31 of 56 subjects presented with parkinsonism, 16 of whom were taking neuroleptics. None of the 15 patients with parkinsonism not related to neuroleptic therapy was diagnosed with epilepsy, compared with 6 of those taking antipsychotics.

CONCLUSIONS

22q11.2DS is characterised by left-handedness and neuropsychiatric features such as cognitive impairment, schizophrenia, epilepsy and parkinsonism. GGE, mostly the JME phenotype, is the predominant epilepsy type. The significant association between 22q11.2DS and parkinsonian features confirms these patients' genetic susceptibility to parkinsonism. Despite the lack of any conclusive evidence, our study suggests a possible relationship between the analysed clinical variables: (1) an inverse correlation between low IQ/psychosis/epilepsy and major cardiac diseases; (2) a direct association between psychosis and both mental delay and epilepsy; and (3) an inverse correlation between parkinsonism and epilepsy.

Epilepsy and seizures in young people with 22q11.2 deletion syndrome: Prevalence and links with other neurodevelopmental disorders

OBJECTIVE

The true prevalence of epileptic seizures and epilepsy in 22q11.2 deletion syndrome (22q11.2DS) is unknown, because previous studies have relied on historical medical record review. Associations of epilepsy with other neurodevelopmental manifestations (eg, specific psychiatric diagnoses) remain unexplored.

METHODS

The primary caregivers of 108 deletion carriers (mean age 13.6 years) and 60 control siblings (mean age 13.1 years) completed a validated epilepsy screening questionnaire. A subsample (n = 44) underwent a second assessment with interview, prolonged electroencephalography (EEG), and medical record and epileptologist review. Intelligence quotient (IQ), psychopathology, and other neurodevelopmental problems were examined using neurocognitive assessment and questionnaire/interview.

RESULTS

Eleven percent (12/108) of deletion carriers had an epilepsy diagnosis (controls 0%, P = 0.004). Fifty-seven of the remaining 96 deletion carriers (59.4%) had seizures or seizurelike symptoms (controls 13.3%, 8/60, P < 0.001). A febrile seizure was reported for 24.1% (26/107) of cases (controls 0%, P < 0.001). One deletion carrier with a clinical history of epilepsy was diagnosed with an additional type of unprovoked seizure during the second assessment. One deletion carrier was newly diagnosed with epilepsy, and two more with possible nonmotor absence seizures. A positive screen on the epilepsy questionnaire was more likely in deletion carriers with lower performance IQ (odds ratio [OR] 0.96, P = 0.018), attention-deficit/hyperactivity disorder (ADHD) (OR 3.28, P = 0.021), autism symptoms (OR 3.86, P = 0.004), and indicative motor coordination disorder (OR 4.56, P = 0.021).

SIGNIFICANCE

Even when accounting for deletion carriers diagnosed with epilepsy, reports of seizures and seizurelike symptoms are common. These may be "true" epileptic seizures in some cases, which are not recognized during routine clinical care. Febrile seizures were far more common in deletion carriers compared to known population risk. A propensity for seizures in 22q11.2DS was associated with cognitive impairment, psychopathology, and motor coordination problems. Future research is required to determine whether this reflects common neurobiologic risk pathways or is a consequence of recurrent seizures.

Prevalence of rearrangements in the 22q11.2 region and population-based risk of neuropsychiatric and developmental disorders in a Danish population: a case-cohort study

BACKGROUND

Although the pathogenic nature of copy number variants (CNVs) on chromosome 22q11.2 has been recognised for decades, unbiased estimates of their population prevalence, mortality, disease risks, and diagnostic trajectories are absent. We aimed to provide the true population prevalence of 22q11.2 CNVs and associated trajectory of disease risk and mortality by use of the unbiased, representative Danish iPSYCH population case cohort.

METHODS

This case-cohort study was done on a population of 86 189 individuals selected from the iPSYCH case cohort of 1 472 762 singletons born in Denmark between May 1, 1981, and Dec 31, 2005, who have a known mother from the Danish Civil Registration System, were residents in Denmark at 1 year of age, and enrolled in the iPSYCH Initiative. We used epidemiological methods in conjunction with nationwide hospital registers to analyse the iPSYCH case cohort of individuals with attention-deficit hyperactivity disorder (ADHD), major depressive disorder, schizophrenia, autism, or bipolar disorder and a random population-based sample. The main outcomes assessed were the population prevalence of 22q11.2 rearrangements, and associated unbiased, population-adjusted estimates and 31-year disease risk trajectories for major neuropsychiatric disorders.

FINDINGS

Population prevalence in the Danish population was one in 3672 (seven of 25 704 [0·027%; 95% CI 0·012-0·057]) for deletions and one in 1606 (17 of 25 704 [0·066%; 0·040-0·107]) for duplications. Mortality after the age of 1 year among carriers was zero, and hazard ratios for neuropsychiatric disorders ranged from 2·60 to 82·44 for both rearrangements. By the age of 32 years, about 10% of individuals with deletions or duplications had developed ADHD, autism, or intellectual disability, and deletion carriers had higher probability than duplication carriers of co-occurring intellectual disability or epilepsy.

INTERPRETATION

The significantly different prevalence of 22q11.2 duplications and deletions indicates distinct selective pressures on these rearrangements. Although risk of congenital abnormalities, developmental delay, and intellectual disability is elevated in deletion carriers, the overall prevalence of neuropsychiatric disorders is higher in duplication carriers, which implies that identification and clinical monitoring should extend beyond congenital traits and into child and adolescent psychiatry.

FUNDING

Capital Region's Research Foundation for Mental Health Research, The Lundbeck Foundation, and US National Institutes of Health.

Epilepsy in 22q11.2 Deletion Syndrome: A Case Series and Literature Review

BACKGROUND

The 22q11.2 deletion syndrome affects multiple organ systems, and the neurological manifestations are an important aspect of this disorder. Many are aware of cardiac anomalies associated with this uncommon genetic disorder. However, the different types of seizures, electroencephalography (EEG), and brain magnetic resonance imaging (MRI) findings seen in this condition are not appreciated.

METHODS

Medical records of four patients with epilepsy due to 22q11.2 deletion syndrome were retrospectively reviewed for documentation of seizure types, EEG, and brain MRI findings. In addition, we also did a literature review of previously reported individuals with unprovoked seizures in this condition.

RESULTS

A review of all published cases including our patients reveals that focal epilepsy (39 of 88, 44%) is the most common type followed by genetic generalized epilepsy (24 of 88, 27%). Diffuse cerebral atrophy and polymicrogyria were the most frequent MRI findings.

CONCLUSIONS

Patients with structural brain abnormalities, especially polymicrogyria and associated epilepsy should have a chromosomal microarray (CMA) performed to screen for the 22q11.2 deletion syndrome. Focal epilepsy and genetic generalized epilepsy are the most frequent epilepsy types reported in this condition.

A Case of 22q11 Deletion Syndrome (22q11DS) with a Panayiotopoulos Epileptic Pattern: Are Additional Copy-Number Variations a Possible Second Hit in Modulating the 22q11DS Phenotype?

"22q11 deletion syndrome" (22q11DS) is a rare genetic syndrome, in which most patients share the same deletion, but their clinical features may vary a great deal. The genetic mechanisms underlying the variable expressivity and reduced penetrance of 22q11DS still have to be fully elucidated. Epilepsy has been reported in about 15.2% of the patients; however, few studies have focused on this topic, and in most cases, a detailed epileptic profile is missing. Since only a minority of patients experience epileptic seizures, 22q11deletion can be considered a predisposing factor, which is not sufficient "per se" to cause epilepsy; to date, no candidate gene for epilepsy has been identified in the deleted region. We report on a 6-year-old girl with 22q11DS presenting a form of epilepsy that can be classified as "Panayiotopoulos syndrome." Array CGH revealed an additional microduplication of 172 kb in 2q37, harboring three genes. One of these, DGKD (diacylglycerol kinase delta), is interrupted by the distal breakpoint of the duplication. DGKD encodes a cytoplasmic enzyme that phosphorylates diacylglycerol to produce phosphatidic acid. This is an important second messenger in a pathway of lipid signaling that has been implicated in epilepsy and other neurological diseases. Disruption of DGKD by a t(X;2) has been previously reported in a patient with epilepsy. The 2q37 microduplication was inherited from her mother, who never experienced epileptic seizures, thus this imbalance is not "per se" sufficient to cause epilepsy. It can be hypothesized that the epileptic phenotype is provoked by the simultaneous presence of 22q11.2 deletion and 2q37 duplication. It has been shown that rare additional copy-number variations (CNVs) outside the 22q11.2 region may modulate the risk of congenital heart defects. It is possible that also for the epileptic phenotype, the additional CNVs may represent an important modifying factor underlying the variable expressivity and incomplete penetrance in the 22q11DS.