The CDKL5 disorder is an independent clinical entity associated with early-onset encephalopathy

Enhanced hippocampal LTP but normal NMDA receptor and AMPA receptor function in a rat model of CDKL5 deficiency disorder

BACKGROUND

Mutations in the X-linked gene cyclin-dependent kinase-like 5 (CDKL5) cause a severe neurological disorder characterised by early-onset epileptic seizures, autism and intellectual disability (ID). Impaired hippocampal function has been implicated in other models of monogenic forms of autism spectrum disorders and ID and is often linked to epilepsy and behavioural abnormalities. Many individuals with CDKL5 deficiency disorder (CDD) have null mutations and complete loss of CDKL5 protein, therefore in the current study we used a Cdkl5-/y rat model to elucidate the impact of CDKL5 loss on cellular excitability and synaptic function of CA1 pyramidal cells (PCs). We hypothesised abnormal pre and/or post synaptic function and plasticity would be observed in the hippocampus of Cdkl5-/y rats.

METHODS

To allow cross-species comparisons of phenotypes associated with the loss of CDKL5, we generated a loss of function mutation in exon 8 of the rat Cdkl5 gene and assessed the impact of the loss of CDLK5 using a combination of extracellular and whole-cell electrophysiological recordings, biochemistry, and histology.

RESULTS

Our results indicate that CA1 hippocampal long-term potentiation (LTP) is enhanced in slices prepared from juvenile, but not adult, Cdkl5-/y rats. Enhanced LTP does not result from changes in NMDA receptor function or subunit expression as these remain unaltered throughout development. Furthermore, Ca2+ permeable AMPA receptor mediated currents are unchanged in Cdkl5-/y rats. We observe reduced mEPSC frequency accompanied by increased spine density in basal dendrites of CA1 PCs, however we find no evidence supporting an increase in silent synapses when assessed using a minimal stimulation protocol in slices. Additionally, we found no change in paired-pulse ratio, consistent with normal release probability at Schaffer collateral to CA1 PC synapses.

CONCLUSIONS

Our data indicate a role for CDKL5 in hippocampal synaptic function and raise the possibility that altered intracellular signalling rather than synaptic deficits contribute to the altered plasticity.

LIMITATIONS

This study has focussed on the electrophysiological and anatomical properties of hippocampal CA1 PCs across early postnatal development. Studies involving other brain regions, older animals and behavioural phenotypes associated with the loss of CDKL5 are needed to understand the pathophysiology of CDD.

CDKL5 deficiency-related neurodevelopmental disorders: a multi-center cohort study in Italy

CDKL5 deficiency disorder (CDD) is a complex clinical condition resulting from non-functional or absent CDKL5 protein, a serine-threonine kinase pivotal for neural maturation and synaptogenesis. The disorder manifests primarily as developmental epileptic encephalopathy, with associated neurological phenotypes, such as hypotonia, movement disorders, visual impairment, and gastrointestinal issues. Its prevalence is estimated at 1 in 40,000-60,000 live births, and it is more prevalent in females due to the lethality of germline mutations in males during fetal development. This Italian multi-center observational study focused on 34 patients with CDKL5-related epileptic encephalopathy, aiming to enhance the understanding of the clinical and molecular aspects of CDD. The study, conducted across 14 pediatric neurology tertiary care centers in Italy, covered various aspects, including phenotypic presentations, seizure types, EEG patterns, treatments, neuroimaging findings, severity of psychomotor delay, and variant-phenotype correlations. The results highlighted the heterogeneity of seizure patterns, with hypermotor-tonic-spasms sequence seizures (HTSS) noted in 17.6% of patients. The study revealed a lack of clear genotype-phenotype correlation within the cohort. The presence of HTSS or HTSS-like at onset resulted a negative prognostic factor for the presence of daily seizures at long-term follow-up in CDD patients. Despite extensive polypharmacotherapy, including medications such as valproic acid, clobazam, cannabidiol, and others, sustained seizure freedom proved elusive, affirming the inherent drug-resistant nature of CDD. The findings underscored the need for further research to explore response rates to different treatments and the potential role of non-pharmacological interventions in managing this challenging disorder.

First report of Tunisian patients with CDKL5-related encephalopathy

OBJECTIVE

Mutations in the cyclin-dependent kinase-like 5 gene (CDKL5) are associated with a wide spectrum of clinical presentations. Early-onset epileptic encephalopathy (EOEE) is the most recognized phenotype. Here we describe phenotypic features in eight Tunisian patients with CDKL5-related encephalopathy.

METHODS

We included all cases with clinical features consistent with CDKL5-related encephalopathy: infantile epileptic spasm, acquired microcephaly, movement disorders and visual impairment. We collected data about seizure types, electroencephalogram, magnetic resonance imaging, and metabolic analysis. The diagnosis of CDKL5 mutation was made thanks to Sanger sequencing with an ABI PRISM 3100-Avant automated DNA sequencer using a Big Dye Terminator Cycle Sequencing Reaction Kit v1.1. and Next Generation Sequencing (NGS) since the development of a gene panel responsible for DEE within the framework of "Strengthening the Sfax University Expertise for diagnosis and management of epileptic encephalopathies".

RESULTS

We collected four boys and four girls aged meanly 6 years old with confirmed mutation on CDKL5 gene. Overall, we identified five de novo CDKL5 mutations including three Frame-shift mutations, one missense mutation, and a splicing variant. The mean age at first seizure onset was 4 months. The first seizure type was infantile epileptic spasm (4/8) followed by tonic (2/8) and myoclonic seizures (2/8). Out of eight cases, four exhibited two stages epileptic course while epilepsy in three other patients progressed on three stages. Regarding development, most cases (6/8) had psychomotor retardation from the start whilst the two others showed psychomotor regression with the onset of seizures. Additional clinical features included visual impairment (7/8), tone abnormalities (7/8), stereotypies (7/8), and acquired microcephaly (6/8).

SIGNIFICANCE

Our present report delineates an unusual phenotype of CDKL5-related encephalopathy with male gender predominance and delayed onset epilepsy. It interestingly described new phenotypic features and uncommon benign developmental profiles in boys, different patterns of CDKL5-epilepsy, neuroimaging findings, and CDKL5 mutational spectrum.

Providing quality care for people with CDKL5 deficiency disorder: A European expert panel opinion on the patient journey

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a developmental and epileptic encephalopathy caused by variants in the CDKL5 gene. The disorder is characterized by intractable early-onset seizures, severe neurodevelopmental delay, hypotonia, motor disabilities, cerebral (cortical) visual impairment and microcephaly. With no disease-modifying therapies available for CDD, treatment is symptomatic with an initial focus on seizure control. Another unmet need in the management of people with CDD is the lack of evidence to aid standardized care and guideline development. To address this gap, experts in CDD and representatives from patient advocacy groups from Denmark, Finland, France, Germany, Italy, Poland, Spain, and the United Kingdom convened to form an Expert Working Group. The aim was to provide an expert opinion consensus on how to ensure quality care in routine clinical practice within the European setting, including in settings with limited experience or resources for multidisciplinary care of CDD and other developmental and epileptic encephalopathies. By means of one-to-one interviews around the current treatment landscape in CDD, insights from the Expert Working Group were collated and developed into a Europe-specific patient journey for individuals with CDD, which was later validated by the group. Further discussions followed to gain consensus of opinions on challenges and potential solutions for achieving quality care in this setting. The panel recognized the benefit of early genetic testing, a holistic personalized approach to seizure control (taking into consideration various factors such as concomitant medications and comorbidities), and age- and comorbidity-dependent multidisciplinary care for optimizing patient outcomes and quality of life. However, their insights and experiences also highlighted much disparity in management approaches and resources across different European countries. Development of standardized European recommendations is required to align realistic diagnostic criteria, treatment goals, and management approaches that can be adapted for different settings. PLAIN LANGUAGE SUMMARY: Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a rare condition caused by a genetic mutation with a broad range of symptoms apparent from early childhood, including epileptic seizures that do not respond to medication and severe delays in development. Due to the lack of guidance on managing CDD, international experts and patient advocates discussed best practices in the care of people with CDD in Europe. The panel agreed that early testing, a personalized approach to managing seizures, and access to care from different disciplines are beneficial. Development of guidelines to ensure that care is standardized would also be valuable.

Biallelic variants identified in 36 Pakistani families and trios with autism spectrum disorder

With its high rate of consanguineous marriages and diverse ethnic population, little is currently understood about the genetic architecture of autism spectrum disorder (ASD) in Pakistan. Pakistan has a highly ethnically diverse population, yet with a high proportion of endogamous marriages, and is therefore anticipated to be enriched for biallelic disease-relate variants. Here, we attempt to determine the underlying genetic abnormalities causing ASD in thirty-six small simplex or multiplex families from Pakistan. Microarray genotyping followed by homozygosity mapping, copy number variation analysis, and whole exome sequencing were used to identify candidate. Given the high levels of consanguineous marriages among these families, autosomal recessively inherited variants were prioritized, however de novo/dominant and X-linked variants were also identified. The selected variants were validated using Sanger sequencing. Here we report the identification of sixteen rare or novel coding variants in fifteen genes (ARAP1, CDKL5, CSMD2, EFCAB12, EIF3H, GML, NEDD4, PDZD4, POLR3G, SLC35A2, TMEM214, TMEM232, TRANK1, TTC19, and ZNF292) in affected members in eight of the families, including ten homozygous variants in four families (nine missense, one loss of function). Three heterozygous de novo mutations were also identified (in ARAP1, CSMD2, and NEDD4), and variants in known X-linked neurodevelopmental disorder genes CDKL5 and SLC35A2. The current study offers information on the genetic variability associated with ASD in Pakistan, and demonstrates a marked enrichment for biallelic variants over that reported in outbreeding populations. This information will be useful for improving approaches for studying ASD in populations where endogamy is commonly practiced.

X-Linked Epilepsies: A Narrative Review

X-linked epilepsies are a heterogeneous group of epileptic conditions, which often overlap with X-linked intellectual disability. To date, various X-linked genes responsible for epilepsy syndromes and/or developmental and epileptic encephalopathies have been recognized. The electro-clinical phenotype is well described for some genes in which epilepsy represents the core symptom, while less phenotypic details have been reported for other recently identified genes. In this review, we comprehensively describe the main features of both X-linked epileptic syndromes thoroughly characterized to date (PCDH19-related DEE, CDKL5-related DEE, MECP2-related disorders), forms of epilepsy related to X-linked neuronal migration disorders (e.g., ARX, DCX, FLNA) and DEEs associated with recently recognized genes (e.g., SLC9A6, SLC35A2, SYN1, ARHGEF9, ATP6AP2, IQSEC2, NEXMIF, PIGA, ALG13, FGF13, GRIA3, SMC1A). It is often difficult to suspect an X-linked mode of transmission in an epilepsy syndrome. Indeed, different models of X-linked inheritance and modifying factors, including epigenetic regulation and X-chromosome inactivation in females, may further complicate genotype-phenotype correlations. The purpose of this work is to provide an extensive and updated narrative review of X-linked epilepsies. This review could support clinicians in the genetic diagnosis and treatment of patients with epilepsy featuring X-linked inheritance.

CDKL5 deficiency disorder and other infantile-onset genetic epilepsies

AIM

To differentiate phenotypic features of individuals with CDKL5 deficiency disorder (CDD) from those of individuals with other infantile-onset epilepsies.

METHOD

We performed a retrospective cohort study and ascertained individuals with CDD and comparison individuals with infantile-onset epilepsy who had epilepsy gene panel testing. We reviewed records, updated variant classifications, and compared phenotypic features. Wilcoxon rank-sum tests and χ2 or Fisher's exact tests were performed for between-cohort comparisons.

RESULTS

We identified 137 individuals with CDD (110 females, 80.3%; median age at last follow-up 3 year 11 months) and 313 individuals with infantile-onset epilepsies (156 females, 49.8%; median age at last follow-up 5 years 2 months; 35% with genetic diagnosis). Features reported significantly more frequently in the CDD group than in the comparison cohort included developmental and epileptic encephalopathy (81% vs 66%), treatment-resistant epilepsy (95% vs 71%), sequential seizures (46% vs 6%), epileptic spasms (66% vs 42%, with hypsarrhythmia in 30% vs 48%), regression (52% vs 29%), evolution to Lennox-Gastaut syndrome (23% vs 5%), diffuse hypotonia (72% vs 36%), stereotypies (69% vs 11%), paroxysmal movement disorders (29% vs 17%), cerebral visual impairment (94% vs 28%), and failure to thrive (38% vs 22%).

INTERPRETATION

CDD, compared with other suspected or confirmed genetic epilepsies presenting in the first year of life, is more often characterized by a combination of treatment-resistant epilepsy, developmental and epileptic encephalopathy, sequential seizures, spasms without hypsarrhythmia, diffuse hypotonia, paroxysmal movement disorders, cerebral visual impairment, and failure to thrive. Defining core phenotypic characteristics will improve precision diagnosis and treatment.

Growth patterns in individuals with CDKL5 deficiency disorder

AIM

To compare growth in individuals with cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder with population norms and to investigate the effect of gastrostomy on growth.

METHOD

The longitudinal study included 353 individuals from the International CDKL5 Disorder Database with any anthropometric measurement in baseline and/or follow-up questionnaires. The British 1990 growth reference was used to determine the age- and sex-standardized z-score. Repeated cross-sectional data were fitted using a Gaussian linear regression model with generalized estimating equations.

RESULTS

All growth parameters were below the general population norm (mean z-scores: weight -0.97, height -0.65, body mass index [BMI] -0.81, head circumference -2.12). The disparity was particularly pronounced for all anthropometric measurements after 4 years of age except for BMI. Moreover, individuals with gastrostomy placement were shown to have a larger decrease than those without.

INTERPRETATION

In addition to weight, height, and BMI, head circumference was also compromised in this disorder. Microcephaly could be considered a helpful diagnostic feature, especially in adults. Any benefit of gastrostomy on weight and BMI was mainly seen in the early years.

Gut microbiota profile in CDKL5 deficiency disorder patients

CDKL5 deficiency disorder (CDD) is a neurodevelopmental condition characterized by global developmental delay, early-onset seizures, intellectual disability, visual and motor impairments. Unlike Rett Syndrome (RTT), CDD lacks a clear regression period. Patients with CDD frequently encounter gastrointestinal (GI) disturbances and exhibit signs of subclinical immune dysregulation. However, the underlying causes of these conditions remain elusive. Emerging studies indicate a potential connection between neurological disorders and gut microbiota, an area completely unexplored in CDD. We conducted a pioneering study, analyzing fecal microbiota composition in individuals with CDD (n = 17) and their healthy relatives (n = 17). Notably, differences in intestinal bacterial diversity and composition were identified in CDD patients. In particular, at genus level, CDD microbial communities were characterized by an increase in the relative abundance of Clostridium_AQ, Eggerthella, Streptococcus, and Erysipelatoclostridium, and by a decrease in Eubacterium, Dorea, Odoribacter, Intestinomonas, and Gemmiger, pointing toward a dysbiotic profile. We further investigated microbiota changes based on the severity of GI issues, seizure frequency, sleep disorders, food intake type, impairment in neuro-behavioral features and ambulation capacity. Enrichment in Lachnoclostridium and Enterobacteriaceae was observed in the microbiota of patients with more severe GI symptoms, while Clostridiaceae, Peptostreptococcaceae, Coriobacteriaceae, Erysipelotrichaceae, Christensenellaceae, and Ruminococcaceae were enriched in patients experiencing daily epileptic seizures. Our findings suggest a potential connection between CDD, microbiota and symptom severity. This study marks the first exploration of the gut-microbiota-brain axis in subjects with CDD. It adds to the growing body of research emphasizing the role of the gut microbiota in neurodevelopmental disorders and opens doors to potential interventions that target intestinal microbes with the aim of improving the lives of patients with CDD.

CDKL5 Deficiency Disorder: Some Lessons Learned 20 Years After the First Description

Loss of function variants in the Cyclin-dependent kinase-like 5 gene (CDKL5) causes CDKL5 deficiency disorder (CDD). Most cases of CDD are due to a de novo missense or truncating variants. The CDKL5 gene was discovered in 1998 as part of the genomic mapping of the chromosome Xp22 region that led to the discovery of the serine-threonine kinases STK9. Since then, there have been significant advancements in the description of the disease in humans, the understanding of the pathophysiology, and the management of the disease. There have been many lessons learned since the initial description of the condition in humans in 2003. In this article, we will focus on pathophysiology, clinical manifestations, with particular focus on seizures because of its relevance to the medical practitioners and researchers and guidelines for management. We finalize the manuscript with the voice of the parents and caregivers, as discussed with the 2019 meeting with the Food and Drug Administration.

Overcoming genetic and cellular complexity to study the pathophysiology of X-linked intellectual disabilities

X-linked genetic causes of intellectual disability (ID) account for a substantial proportion of cases and remain poorly understood, in part due to the heterogeneous expression of X-linked genes in females. This is because most genes on the X chromosome are subject to random X chromosome inactivation (XCI) during early embryonic development, which results in a mosaic pattern of gene expression for a given X-linked mutant allele. This mosaic expression produces substantial complexity, especially when attempting to study the already complicated neural circuits that underly behavior, thus impeding the understanding of disease-related pathophysiology and the development of therapeutics. Here, we review a few selected X-linked forms of ID that predominantly affect heterozygous females and the current obstacles for developing effective therapies for such disorders. We also propose a genetic strategy to overcome the complexity presented by mosaicism in heterozygous females and highlight specific tools for studying synaptic and circuit mechanisms, many of which could be shared across multiple forms of intellectual disability.

Cell type-specific expression, regulation and compensation of CDKL5 activity in mouse brain

CDKL5 is a brain-enriched serine/threonine kinase, associated with a profound developmental and epileptic encephalopathy called CDKL5 deficiency disorder (CDD). To design targeted therapies for CDD, it is essential to determine where CDKL5 is expressed and is active in the brain and test if compensatory mechanisms exist at cellular level. We generated conditional Cdkl5 knockout mice in excitatory neurons, inhibitory neurons and astrocytes. To assess CDKL5 activity, we utilized a phosphospecific antibody for phosphorylated EB2, a well-known substrate of CDKL5. We found that CDKL5 and EB2 pS222 were prominent in excitatory and inhibitory neurons but were not detected in astrocytes. We observed that approximately 15-20% of EB2 pS222 remained in Cdkl5 knockout brains and primary neurons. Surprisingly, the remaining phosphorylation was modulated by NMDA and PP1/PP2A in neuronal CDKL5 knockout cultures, indicating the presence of a compensating kinase. Using a screen of candidate kinases with highest homology to the CDKL5 kinase domain, we found that CDKL2 and ICK can phosphorylate EB2 S222 in HEK293T cells and in primary neurons. We then generated Cdkl5/Cdkl2 dual knockout mice to directly test if CDKL2 phosphorylates EB2 in vivo and found that CDKL2 phosphorylates CDKL5 substrates in the brain. This study is the first indication that CDKL2 could potentially replace CDKL5 functions in the brain, alluding to novel therapeutic possibilities.

Current Overview of CDKL-5 Deficiency Disorder Treatment

CDKL5 deficiency disorder (CDD) is a complex of clinical symptoms resulting from the presence of non-functional or absent CDKL5 protein, a serine-threonine kinase involved in neural maturation and synaptogenesis [...].

Deciphering the roles of subcellular distribution and interactions involving the MEF2 binding region, the ankyrin repeat binding motif and the catalytic site of HDAC4 in Drosophila neuronal morphogenesis

BACKGROUND

Dysregulation of nucleocytoplasmic shuttling of histone deacetylase 4 (HDAC4) is associated with several neurodevelopmental and neurodegenerative disorders. Consequently, understanding the roles of nuclear and cytoplasmic HDAC4 along with the mechanisms that regulate nuclear entry and exit is an area of concerted effort. Efficient nuclear entry is dependent on binding of the transcription factor MEF2, as mutations in the MEF2 binding region result in cytoplasmic accumulation of HDAC4. It is well established that nuclear exit and cytoplasmic retention are dependent on 14-3-3-binding, and mutations that affect binding are widely used to induce nuclear accumulation of HDAC4. While regulation of HDAC4 shuttling is clearly important, there is a gap in understanding of how the nuclear and cytoplasmic distribution of HDAC4 impacts its function. Furthermore, it is unclear whether other features of the protein including the catalytic site, the MEF2-binding region and/or the ankyrin repeat binding motif influence the distribution and/or activity of HDAC4 in neurons. Since HDAC4 functions are conserved in Drosophila, and increased nuclear accumulation of HDAC4 also results in impaired neurodevelopment, we used Drosophila as a genetic model for investigation of HDAC4 function.

RESULTS

Here we have generated a series of mutants for functional dissection of HDAC4 via in-depth examination of the resulting subcellular distribution and nuclear aggregation, and correlate these with developmental phenotypes resulting from their expression in well-established models of neuronal morphogenesis of the Drosophila mushroom body and eye. We found that in the mushroom body, forced sequestration of HDAC4 in the nucleus or the cytoplasm resulted in defects in axon morphogenesis. The actions of HDAC4 that resulted in impaired development were dependent on the MEF2 binding region, modulated by the ankyrin repeat binding motif, and largely independent of an intact catalytic site. In contrast, disruption to eye development was largely independent of MEF2 binding but mutation of the catalytic site significantly reduced the phenotype, indicating that HDAC4 acts in a neuronal-subtype-specific manner.

CONCLUSIONS

We found that the impairments to mushroom body and eye development resulting from nuclear accumulation of HDAC4 were exacerbated by mutation of the ankyrin repeat binding motif, whereas there was a differing requirement for the MEF2 binding site and an intact catalytic site. It will be of importance to determine the binding partners of HDAC4 in nuclear aggregates and in the cytoplasm of these tissues to further understand its mechanisms of action.

Long-term treatment with ganaxolone for seizures associated with cyclin-dependent kinase-like 5 deficiency disorder: Two-year open-label extension follow-up

OBJECTIVE

In the placebo-controlled, double-blind phase of the Marigold study (NCT03572933), ganaxolone significantly reduced major motor seizure frequency (MMSF) in patients with cyclin-dependent kinase-like 5 deficiency disorder (CDD). We report 2-year safety and clinical outcomes data from the open-label extension (OLE) phase of Marigold.

METHODS

Patients with CDD who completed the double-blind phase were eligible to continue in the OLE. Efficacy assessments included MMSF reduction from prerandomization baseline, responder rates, and Clinical Global Impression-Improvement scores, including assessment of seizure intensity and duration (CGI-CSID). Safety assessments included treatment-emergent adverse events (TEAEs) and TEAEs leading to discontinuation.

RESULTS

Of 101 patients who enrolled in Marigold, 88 (87.1%) entered the OLE (median age = 5 years, 79.5% female). Median 28-day MMSF at baseline was 50.6. At 2 years in the OLE (months 22-24), MMSF was reduced by a median of 48.2% (n = 50); when missing data were imputed, median reduction in MMSF was 43.8% using a mixed effects model and 27.4% using a last observation carried forward model. During months 22-24, 23 of 50 (46.0%) patients experienced reductions in MMSF of ≥50%; 12 of 50 (24.0%) patients experienced MMSF reductions of ≥75%. During months 22-24, 40 of 49 (81.6%) patients were rated by caregivers as having improvement in seizure-related outcomes based on CGI-CSID scores. Thirty-seven patients discontinued ganaxolone due to lack of efficacy (n = 13), withdrawal by caregiver (n = 12), adverse event (n = 10), physician decision (n = 1), or death (n = 1; unrelated to study drug). The most common treatment-related TEAEs were somnolence (17.0%), seizure (11.4%), and decreased appetite (5.7%). Patients reported serious TEAEs (n = 28, 31.8%); those reported in ≥3% of patients were seizure (n = 6), pneumonia (n = 5), acute respiratory failure (n = 3), aspiration pneumonia (n = 3), and dehydration (n = 3).

SIGNIFICANCE

Sustained reductions in MMSF at 2 years in the OLE support the efficacy of ganaxolone in seizures associated with CDD. Safety findings in the OLE were consistent with the double-blind phase.

Comprehensive Transcriptomic Investigation of Rett Syndrome Reveals Increasing Complexity Trends from Induced Pluripotent Stem Cells to Neurons with Implications for Enriched Pathways

Rett syndrome (RTT) is a rare genetic neurodevelopmental disorder that has no cure apart from symptomatic treatments. While intense research efforts are required to fulfill this unmet need, the fundamental challenge is to obtain sufficient patient data. In this study, we used human transcriptomic data of four different sample types from RTT patients including induced pluripotent stem cells, differentiated neural progenitor cells, differentiated neurons, and postmortem brain tissues with an increasing in vivo-like complexity to unveil specific trends in gene expressions across the samples. Based on DEG analysis, we identified F8A3, CNTN6, RPE65, and COL19A1 to have differential expression levels in three sample types and also observed previously reported genes such as MECP2, FOXG1, CACNA1G, SATB2, GABBR2, MEF2C, KCNJ10, and CUX2 in our study. Considering the significantly enriched pathways for each sample type, we observed a consistent increase in numbers from iPSCs to NEUs where MECP2 displayed profound effects. We also validated our GSEA results by using single-cell RNA-seq data. In WGCNA, we elicited a connection among MECP2, TNRC6A, and HOXA5. Our findings highlight the utility of transcriptomic analyses to determine genes that might lead to therapeutic strategies.

Rett and Rett-related disorders: Common mechanisms for shared symptoms?

Rett syndrome is a neurodevelopmental disorder caused by loss-of-function mutations in the methyl-CpG binding protein-2 (MeCP2) gene that is characterized by epilepsy, intellectual disability, autistic features, speech deficits, and sleep and breathing abnormalities. Neurologically, patients with all three disorders display microcephaly, aberrant dendritic morphology, reduced spine density, and an imbalance of excitatory/inhibitory signaling. Loss-of-function mutations in the cyclin-dependent kinase-like 5 (CDKL5) and FOXG1 genes also cause similar behavioral and neurobiological defects and were referred to as congenital or variant Rett syndrome. The relatively recent realization that CDKL5 deficiency disorder (CDD), FOXG1 syndrome, and Rett syndrome are distinct neurodevelopmental disorders with some distinctive features have resulted in separate focus being placed on each disorder with the assumption that distinct molecular mechanisms underlie their pathogenesis. However, given that many of the core symptoms and neurological features are shared, it is likely that the disorders share some critical molecular underpinnings. This review discusses the possibility that deregulation of common molecules in neurons and astrocytes plays a central role in key behavioral and neurological abnormalities in all three disorders. These include KCC2, a chloride transporter, vGlut1, a vesicular glutamate transporter, GluD1, an orphan-glutamate receptor subunit, and PSD-95, a postsynaptic scaffolding protein. We propose that reduced expression or activity of KCC2, vGlut1, PSD-95, and AKT, along with increased expression of GluD1, is involved in the excitatory/inhibitory that represents a key aspect in all three disorders. In addition, astrocyte-derived brain-derived neurotrophic factor (BDNF), insulin-like growth factor 1 (IGF-1), and inflammatory cytokines likely affect the expression and functioning of these molecules resulting in disease-associated abnormalities.

Voluntary Running Improves Behavioral and Structural Abnormalities in a Mouse Model of CDKL5 Deficiency Disorder

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a rare neurodevelopmental disease caused by mutations in the X-linked CDKL5 gene. CDD is characterized by a broad spectrum of clinical manifestations, including early-onset refractory epileptic seizures, intellectual disability, hypotonia, visual disturbances, and autism-like features. The Cdkl5 knockout (KO) mouse recapitulates several features of CDD, including autistic-like behavior, impaired learning and memory, and motor stereotypies. These behavioral alterations are accompanied by diminished neuronal maturation and survival, reduced dendritic branching and spine maturation, and marked microglia activation. There is currently no cure or effective treatment to ameliorate the symptoms of the disease. Aerobic exercise is known to exert multiple beneficial effects in the brain, not only by increasing neurogenesis, but also by improving motor and cognitive tasks. To date, no studies have analyzed the effect of physical exercise on the phenotype of a CDD mouse model. In view of the positive effects of voluntary running on the brain of mouse models of various human neurodevelopmental disorders, we sought to determine whether voluntary daily running, sustained over a month, could improve brain development and behavioral defects in Cdkl5 KO mice. Our study showed that long-term voluntary running improved the hyperlocomotion and impulsivity behaviors and memory performance of Cdkl5 KO mice. This is correlated with increased hippocampal neurogenesis, neuronal survival, spine maturation, and inhibition of microglia activation. These behavioral and structural improvements were associated with increased BDNF levels. Given the positive effects of BDNF on brain development and function, the present findings support the positive benefits of exercise as an adjuvant therapy for CDD.

Gastrointestinal Dysfunction in Genetically Defined Neurodevelopmental Disorders

Gastrointestinal symptoms are common in most forms of neurodevelopment disorders (NDDs) such as in autism spectrum disorders (ASD). The current patient-reported outcome measures with validated questionnaires used in the general population of children without NDDS cannot be used in the autistic individuals. We explore here the multifactorial pathophysiology of ASD and the role of genetics and the environment in this disease spectrum and focus instead on possible diagnostics that could provide future objective insight into the connection of the gut-brain-microbiome in this disease entity. We provide our own data from both humans and a zebrafish model of ASD called Phelan-McDermid Syndrome. We hope that this review highlights the gaps in our current knowledge on many of these profound NDDs and that it provides a future framework upon which clinicians and researchers can build and network with other interested multidisciplinary specialties.

Rett Syndrome: A Tale of Altered Genetics, Synaptic Plasticity, and Neurodevelopmental Dynamics

Rett syndrome (RTT) is a neurodevelopmental disorder that is a leading cause of severe cognitive and physical impairment. RTT typically occurs in females, although rare cases of males with the disease exist. Its genetic cause, symptoms, and clinical progression timeline have also become well-documented since its initial discovery. However, a relatively late diagnosis and lack of an available cure signify that our understanding of the disease is incomplete. Innovative research methods and tools are thereby helping to fill gaps in our knowledge of RTT. Specifically, mouse models of RTT, video analysis, and retrospective parental analysis are well-established tools that provide valuable insights into RTT. Moreover, current and anticipated treatment options are improving the quality of life of the RTT patient population. Collectively, these developments are creating optimistic future perspectives for RTT.

Research progress on the pathogenesis of CDKL5 pathogenic variants and related encephalopathy

Cyclin-dependent kinase-like 5 (CDKL5) is a gene encoding a serine/threonine kinase that possesses an N-terminal catalytic domain and a large C-terminal domain and is located on the short arm of the X-chromosome at position 22 (Xp22). CDKL5 regulates neuronal migration, axonal growth, dendritic morphogenesis, and synaptic development and affects synaptic function. Pathogenic variants include deletions, truncations, splice variants, and missense variants. The specificity of CDKL5 is mainly determined by the shared sequence of amino acid residues, which is the phosphorylation site of the target protein with the motif Arg-Pro-X-Ser/Thr-Ala/Pro/Gly/Ser (R-P-X-[S/T]-[A/G/P/S]). Developmental encephalopathy caused by pathogenic variants of CDKL5 has a variety of nervous system symptoms, such as epilepsy, hypotonia, growth retardation, dyskinesia, cortical visual impairment, sleep disorders, and other clinical symptoms. This review summarizes the mechanism of CDKL5-induced allogeneic lesions in the nervous system and the clinical manifestations of related encephalopathy.   Conclusion: This review clarifies CDKL5's participation in neurodevelopmental diseases as well as its crucial function in dividing cells, cultured neurons, knockout mice, and human iPSC-derived neurons. CDKL5 variants help identify clinical diagnostic biomarkers. Although a few direct substrates of CDKL5 have been identified, more must be found in order to fully comprehend the signaling pathways connected to CDKL5 in the brain and the mechanisms that underlie its activities.

Discovery of a Potent and Selective CDKL5/GSK3 Chemical Probe That Is Neuroprotective

Despite mediating several essential processes in the brain, including during development, cyclin-dependent kinase-like 5 (CDKL5) remains a poorly characterized human protein kinase. Accordingly, its substrates, functions, and regulatory mechanisms have not been fully described. We realized that availability of a potent and selective small molecule probe targeting CDKL5 could enable illumination of its roles in normal development as well as in diseases where it has become aberrant due to mutation. We prepared analogs of AT-7519, a compound that has advanced to phase II clinical trials and is a known inhibitor of several cyclin-dependent kinases (CDKs) and cyclin-dependent kinase-like kinases (CDKLs). We identified analog 2 as a highly potent and cell-active chemical probe for CDKL5/GSK3 (glycogen synthase kinase 3). Evaluation of its kinome-wide selectivity confirmed that analog 2 demonstrates excellent selectivity and only retains GSK3α/β affinity. We next demonstrated the inhibition of downstream CDKL5 and GSK3α/β signaling and solved a co-crystal structure of analog 2 bound to human CDKL5. A structurally similar analog (4) proved to lack CDKL5 affinity and maintain potent and selective inhibition of GSK3α/β, making it a suitable negative control. Finally, we used our chemical probe pair (2 and 4) to demonstrate that inhibition of CDKL5 and/or GSK3α/β promotes the survival of human motor neurons exposed to endoplasmic reticulum stress. We have demonstrated a neuroprotective phenotype elicited by our chemical probe pair and exemplified the utility of our compounds to characterize the role of CDKL5/GSK3 in neurons and beyond.

Efficacy, safety, and tolerability of soticlestat as adjunctive therapy for the treatment of seizures in patients with Dup15q syndrome or CDKL5 deficiency disorder in an open-label signal-finding phase II study (ARCADE)

OBJECTIVE

Chromosome 15q duplication (Dup15q) syndrome and cyclin‑dependent kinase-like 5 deficiency disorder (CDD) are rare neurodevelopmental disorders associated with epileptic encephalopathies, with a lack of specifically approved treatment options. ARCADE assessed the efficacy and safety of adjunctive soticlestat (TAK-935) for the treatment of seizures in patients with Dup15q syndrome or CDD (NCT03694275).

METHODS

ARCADE was a phase II, open-label, pilot study of soticlestat (≤300 mg/day twice daily, weight-adjusted) in pediatric and adult patients 2-55 years of age with Dup15q syndrome or CDD who experienced ≥3 motor seizures per month in the 3 months before screening and at baseline. The 20-week treatment period consisted of a dose-optimization period and a 12-week maintenance period. Efficacy endpoints included the change from baseline in motor seizure frequency during the maintenance period and the proportion of treatment responders. Safety endpoints included the incidence of treatment-emergent adverse effects (TEAEs).

RESULTS

The modified-intent-to-treat population included 20 participants who received ≥1 dose of soticlestat and had ≥1 efficacy assessment (Dup15q syndrome, n = 8; CDD, n = 12). Soticlestat administration during the maintenance period was associated with a median change from baseline in motor seizure frequency of +11.7% in the Dup15q syndrome group and -23.6% in the CDD group. Reductions in all seizure frequency of -23.4% and -30.5% were also observed during the maintenance period in the Dup15q syndrome group and the CDD group, respectively. Most TEAEs were of mild or moderate severity. Serious TEAEs were reported by three patients (15.0%); none were considered drug related. The most common TEAEs were constipation, rash, and seizure. No deaths were reported.

CONCLUSIONS

Adjunctive soticlestat treatment was associated with a decrease in motor seizure frequency from baseline in patients with CDD and a decrease in all seizure frequency in both patient groups. Soticlestat treatment was associated with an increase in motor seizure frequency in patients with Dup15q syndrome.

Epilepsy-Related CDKL5 Deficiency Slows Synaptic Vesicle Endocytosis in Central Nerve Terminals

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a severe early-onset epileptic encephalopathy resulting mainly from de novo mutations in the X-linked CDKL5 gene. To determine whether loss of presynaptic CDKL5 function contributes to CDD, we examined synaptic vesicle (SV) recycling in primary hippocampal neurons generated from Cdkl5 knockout rat males. Using a genetically encoded reporter, we revealed that CDKL5 is selectively required for efficient SV endocytosis. We showed that CDKL5 kinase activity is both necessary and sufficient for optimal SV endocytosis, since kinase-inactive mutations failed to correct endocytosis in Cdkl5 knockout neurons, whereas the isolated CDKL5 kinase domain fully restored SV endocytosis kinetics. Finally, we demonstrated that CDKL5-mediated phosphorylation of amphiphysin 1, a putative presynaptic target, is not required for CDKL5-dependent control of SV endocytosis. Overall, our findings reveal a key presynaptic role for CDKL5 kinase activity and enhance our insight into how its dysfunction may culminate in CDD.SIGNIFICANCE STATEMENT Loss of cyclin-dependent kinase like 5 (CDKL5) function is a leading cause of monogenic childhood epileptic encephalopathy. However, information regarding its biological role is scarce. In this study, we reveal a selective presynaptic role for CDKL5 in synaptic vesicle endocytosis and that its protein kinase activity is both necessary and sufficient for this role. The isolated protein kinase domain is sufficient to correct this loss of function, which may facilitate future gene therapy strategies if presynaptic dysfunction is proven to be central to the disorder. It also reveals that a CDKL5-specific substrate is located at the presynapse, the phosphorylation of which is required for optimal SV endocytosis.

The gut-brain connection: Exploring the influence of the gut microbiota on neuroplasticity and neurodevelopmental disorders

Neuroplasticity refers to the ability of brain circuits to reorganize and change the properties of the network, resulting in alterations in brain function and behavior. It is traditionally believed that neuroplasticity is influenced by external stimuli, learning, and experience. Intriguingly, there is new evidence suggesting that endogenous signals from the body's periphery may play a role. The gut microbiota, a diverse community of microorganisms living in harmony with their host, may be able to influence plasticity through its modulation of the gut-brain axis. Interestingly, the maturation of the gut microbiota coincides with critical periods of neurodevelopment, during which neural circuits are highly plastic and potentially vulnerable. As such, dysbiosis (an imbalance in the gut microbiota composition) during early life may contribute to the disruption of normal developmental trajectories, leading to neurodevelopmental disorders. This review aims to examine the ways in which the gut microbiota can affect neuroplasticity. It will also discuss recent research linking gastrointestinal issues and bacterial dysbiosis to various neurodevelopmental disorders and their potential impact on neurological outcomes.

Cardiac Functional and Structural Abnormalities in a Mouse Model of CDKL5 Deficiency Disorder

CDKL5 (cyclin-dependent kinase-like 5) deficiency disorder (CDD) is a severe neurodevelopmental disease that mostly affects girls, who are heterozygous for mutations in the X-linked CDKL5 gene. Mutations in the CDKL5 gene lead to a lack of CDKL5 protein expression or function and cause numerous clinical features, including early-onset seizures, marked hypotonia, autistic features, gastrointestinal problems, and severe neurodevelopmental impairment. Mouse models of CDD recapitulate several aspects of CDD symptomology, including cognitive impairments, motor deficits, and autistic-like features, and have been useful to dissect the role of CDKL5 in brain development and function. However, our current knowledge of the function of CDKL5 in other organs/tissues besides the brain is still quite limited, reducing the possibility of broad-spectrum interventions. Here, for the first time, we report the presence of cardiac function/structure alterations in heterozygous Cdkl5 +/− female mice. We found a prolonged QT interval (corrected for the heart rate, QTc) and increased heart rate in Cdkl5 +/− mice. These changes correlate with a marked decrease in parasympathetic activity to the heart and in the expression of the Scn5a and Hcn4 voltage-gated channels. Interestingly, Cdkl5 +/− hearts showed increased fibrosis, altered gap junction organization and connexin-43 expression, mitochondrial dysfunction, and increased ROS production. Together, these findings not only contribute to our understanding of the role of CDKL5 in heart structure/function but also document a novel preclinical phenotype for future therapeutic investigation.

Genetic and clinical variations of developmental epileptic encephalopathies

OBJECTIVE

The concept of 'developmental and epileptic encephalopathy (DEE)' recognises that in infants presenting with severe early-onset epilepsy, neurodevelopmental comorbidity may be attributable to both the underlying cause and to adverse effects of uncontrolled epileptic activity. There is no direct genotype - phenotype correlation in DEEs. This study aimed to report the genetic and phenotypic differences in patients with DEE.

METHODS

Genetic evaluations of the patients were performed due to epilepsy combined with developmental delay, epileptic encephalopathy, motor deficits, autistic features, or cognitive impairment. Patients were assessed for demographic characteristics, medical history, family history, psychomotor development, seizure control interventions, electroencephalogram (EEG) and magnetic resonance imaging (MRI) findings.

RESULTS

This study included 20 children aged 0-16 years who were diagnosed as having DEE.The types of DEE detected in our study were DEE 2, 4, 6B, 7, 11, 26, 30, 33, 35, 42, 58, 62, and 67.Status epilepticus was recorded in only DEE7. The most common EEG abnormality was multifocal epileptic discharges (35%,) followed by burst-suppression patterns in patients with neonatal-onset seizures. Thirteen of the children were aged over 2 years, two (15%) were non-ambulatory and six (46%) were non-verbal. MRI scans were normal in 80% of the patients. Refractory epilepsy seen in 33% of cases.De-novo mutation, microcephaly and dysmorphic findings accompany resistant seizures and are associated with poor prognosis.

DISCUSSION

For patients with movement disorders, developmental delay, autism, and ID with or without epilepsy in any period of their life, next-generation sequencing is the only diagnostic technique available, with genetic analysis often being the only diagnostic method.

A Potent and Selective CDKL5/GSK3 Chemical Probe is Neuroprotective

Despite mediating several essential processes in the brain, including during development, cyclin-dependent kinase-like 5 (CDKL5) remains a poorly characterized human protein kinase. Accordingly, its substrates, functions, and regulatory mechanisms have not been fully described. We realized that availability of a potent and selective small molecule probe targeting CDKL5 could enable illumination of its roles in normal development as well as in diseases where it has become aberrant due to mutation. We prepared analogs of AT-7519, a known inhibitor of several cyclin dependent and cyclin-dependent kinase-like kinases that has been advanced into Phase II clinical trials. We identified analog 2 as a highly potent and cell-active chemical probe for CDKL5/GSK3 (glycogen synthase kinase 3). Evaluation of its kinome-wide selectivity confirmed that analog 2 demonstrates excellent selectivity and only retains GSK3α/β affinity. As confirmation that our chemical probe is a high-quality tool to use in directed biological studies, we demonstrated inhibition of downstream CDKL5 and GSK3α/β signaling and solved a co-crystal structure of analog 2 bound to CDKL5. A structurally similar analog ( 4 ) proved to lack CDKL5 affinity and maintain potent and selective inhibition of GSK3α/β. Finally, we used our chemical probe pair ( 2 and 4 ) to demonstrate that inhibition of CDKL5 and/or GSK3α/β promotes the survival of human motor neurons exposed to endoplasmic reticulum (ER) stress. We have demonstrated a neuroprotective phenotype elicited by our chemical probe pair and exemplified the utility of our compounds to characterize the role of CDKL5/GSK3 in neurons and beyond.

Factors influencing the attainment of major motor milestones in CDKL5 deficiency disorder

This study investigated the influence of factors at birth and in infancy on the likelihood of achieving major motor milestones in CDKL5 Deficiency Disorder (CDD). Data on 350 individuals with a pathogenic CDKL5 variant was sourced from the International CDKL5 Disorder Database. A first model included factors available at birth (e.g., sex, variant group and mosaicism) and the second additionally included factors available during infancy (e.g., age at seizure onset, number of anti-seizure medications used, experience of a honeymoon period and formal therapy). Cox regression was used to model the time to achieve the milestones. The probability of attaining the outcomes at specific ages was estimated by evaluating the time-to-event function at specific covariate values. Independent sitting and walking were achieved by 177/350 and 57/325 children respectively. By seven years of age, 67.1% of females but only 37.3% of males could sit independently. About a quarter each of females and males achieved independent walking by eight and six years, respectively. When observed from birth, female gender, a late truncating variant and mosaicism impacted most positively on the likelihood of independent sitting. When observed from one year, later seizure onset and experiencing a honeymoon period also improved the likelihood of independent sitting. Factors that favoured sitting (except gender) also improved walking. Having a truncating variant between aa178 and aa781 reduced the likelihood of achieving independent sitting and walking. It is possible to utilise factors occurring early in life to inform the likelihood of future motor development in CDD.

CDKL5-associated developmental and epileptic encephalopathy: A long-term, longitudinal electroclinical study of 22 cases

OBJECTIVE

The study was conducted to analyze the possible diagnostic value of the electroclinical semiology of the epileptic seizures.

METHODS

We evaluated the medical records of 17 females and 5 males with CDKL5 deficiency disorder (CDD) considering the long-term evolution, including the polygraphic video-EEG recordings.

RESULTS

We recognized three disease phases. We found that the seizure semiology was already recognizable in the first phase of the syndrome. In the short-term evolution, all patients had focal motor and 12/21 hypermotor seizures. Both epileptic spasms and myoclonic seizures were already present in more than half of the cases in the first 2 months after onset. In the second phase, the intermediate period, the polymorphic pattern was maintained, but in eight patients the electroclinical pattern of epileptic encephalopathy with hypsarrhythmia appeared. In the long-term period, the seizure polymorphism continued but myoclonic and epileptic spasms diminished. Tonic seizures appeared in the last 2 phases. Progressively, with the aggravation of seizures and paroxysmal EEG abnormalities impairment of the neurocognitive status was observed. Severe behavioral disturbances were seen in eight and autistic-like features in 14.

CONCLUSION

CDD is a true developmental and epileptic encephalopathy with a specific etiology characterized by the early appearance of epileptic seizures that quickly become polymorphic and drug resistant in infants that are most often female and already have neurological impairment. Polygraphic video-EEG recordings are important to recognize ictal events of the association of hypermotor seizures, epileptic spasms in clusters, and massive myoclonic jerks, already present at onset.

Difficulties in the differential diagnosis of Angelman’s syndrome

Angelman syndrome is a rare neurogenetic disease caused by the loss of the function of the maternal allele of the UBE3A gene on chromosome 15 (site 15q11.2–q13) and is characterized by severe mental retardation, lack of speech, epilepsy, microcephaly and a characteristic facial phenotype with a unique behavior in the form of frequent laughter. The combination of microcephaly, epilepsy, speechlessness and mental retardation poses a problem for differential diagnosis with many genetic diseases presenting with similar symptoms. Epileptic encephalopathy due to CDKL5 gene mutation and Rett syndrome have the greatest similarity. The hallmark of Angelman syndrome are laughter attacks and specific EEG changes. The authors have presented a table of the differential diagnosis of Angelman syndrome with some phenotypically similar genetic syndromes, indicating the most significant distinguishing features, which should facilitate for the pediatrician and neurologist the diagnostic path of establishing the correct diagnosis.

Bone Tissue and the Nervous System: What Do They Have in Common?

Degenerative diseases affecting bone tissues and the brain represent important problems with high socio-economic impact. Certain bone diseases, such as osteoporosis, are considered risk factors for the progression of neurological disorders. Often, patients with neurodegenerative diseases have bone fractures or reduced mobility linked to osteoarthritis. The bone is a dynamic tissue involved not only in movement but also in the maintenance of mineral metabolism. Bone is also associated with the generation of both hematopoietic stem cells (HSCs), and thus the generation of the immune system, and mesenchymal stem cells (MSCs). Bone marrow is a lymphoid organ and contains MSCs and HSCs, both of which are involved in brain health via the production of cytokines with endocrine functions. Hence, it seems clear that bone is involved in the regulation of the neuronal system and vice versa. This review summarizes the recent knowledge on the interactions between the nervous system and bone and highlights the importance of the interaction between nerve and bone cells. In addition, experimental models that study the interaction between nerve and skeletal cells are discussed, and innovative models are suggested to better evaluate the molecular interactions between these two cell types.

Wide range of phenotypic severity in individuals with late truncations unique to the predominant CDKL5 transcript in the brain

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is caused by heterozygous or hemizygous variants in CDKL5 and is characterized by refractory epilepsy, cognitive and motor impairments, and cerebral visual impairment. CDKL5 has multiple transcripts, of which the longest transcripts, NM_003159 and NM_001037343, have been used historically in clinical laboratory testing. However, the transcript NM_001323289 is the most highly expressed in brain and contains 170 nucleotides at the 3' end of its last exon that are noncoding in other transcripts. Two truncating variants in this region have been reported in association with a CDD phenotype. To clarify the significance and range of phenotypes associated with late truncating variants in this region of the predominant transcript in the brain, we report detailed information on two individuals, updated clinical information on a third individual, and a summary of published and unpublished individuals reported in ClinVar. The two new individuals (one male and one female) each had a relatively mild clinical presentation including periods of pharmaco-responsive epilepsy, independent walking and limited purposeful communication skills. A previously reported male continued to have a severe phenotype. Overall, variants in this region demonstrate a range of clinical severity consistent with reports in CDD but with the potential for milder presentation.

Behavioral impulsivity is associated with pupillary alterations and hyperactivity in CDKL5 mutant mice

Cyclin-dependent kinase-like 5 (Cdkl5) deficiency disorder (CDD) is a severe neurodevelopmental condition caused by mutations in the X-linked Cdkl5 gene. CDD is characterized by early-onset seizures in the first month of life, intellectual disability, motor and social impairment. No effective treatment is currently available and medical management is only symptomatic and supportive. Recently, mouse models of Cdkl5 disorder have demonstrated that mice lacking Cdkl5 exhibit autism-like phenotypes, hyperactivity and dysregulations of the arousal system, suggesting the possibility to use these features as translational biomarkers. In this study, we tested Cdkl5 male and female mutant mice in an appetitive operant conditioning chamber to assess cognitive and motor abilities, and performed pupillometry to assess the integrity of the arousal system. Then, we evaluated the performance of artificial intelligence models to classify the genotype of the animals from the behavioral and physiological phenotype. The behavioral results show that CDD mice display impulsivity, together with low levels of cognitive flexibility and perseverative behaviors. We assessed arousal levels by simultaneously recording pupil size and locomotor activity. Pupillometry reveals in CDD mice a smaller pupil size and an impaired response to unexpected stimuli associated with hyperlocomotion, demonstrating a global defect in arousal modulation. Finally, machine learning reveals that both behavioral and pupillometry parameters can be considered good predictors of CDD. Since early diagnosis is essential to evaluate treatment outcomes and pupillary measures can be performed easily, we proposed the monitoring of pupil size as a promising biomarker for CDD.

Rodent Models of Audiogenic Epilepsy: Genetic Aspects, Advantages, Current Problems and Perspectives

Animal models of epilepsy are of great importance in epileptology. They are used to study the mechanisms of epileptogenesis, and search for new genes and regulatory pathways involved in the development of epilepsy as well as screening new antiepileptic drugs. Today, many methods of modeling epilepsy in animals are used, including electroconvulsive, pharmacological in intact animals, and genetic, with the predisposition for spontaneous or refractory epileptic seizures. Due to the simplicity of manipulation and universality, genetic models of audiogenic epilepsy in rodents stand out among this diversity. We tried to combine data on the genetics of audiogenic epilepsy in rodents, the relevance of various models of audiogenic epilepsy to certain epileptic syndromes in humans, and the advantages of using of rodent strains predisposed to audiogenic epilepsy in current epileptology.

Quality of life beyond diagnosis in intellectual disability - Latent profiling

OBJECTIVE

To compare quality of life (QOL) across diagnoses associated with intellectual disability, construct QOL profiles and evaluate membership by diagnostic group, function and comorbidities.

METHOD

Primary caregivers of 526 children with intellectual disability (age 5-18 years) and a diagnosis of cerebral palsy, autism spectrum disorder, Down syndrome, CDKL5 deficiency disorder or Rett syndrome completed the Quality of Life Inventory-Disability (QI-Disability) questionnaire. Latent profile analysis of the QI-Disability domain scores was conducted.

RESULTS

The mean (SD) total QOL score was 67.8 (13.4), ranging from 60.3 (14.6) for CDD to 77.5 (11.7) for Down syndrome. Three classes describing domain scores were identified: Class 1 was characterised by higher domain scores overall but poorer negative emotions scores; Class 2 by average to high scores for most domains but low independence scores; and Class 3 was characterised by low positive emotions, social interaction, and leisure and the outdoors scores, and extremely low independence scores. The majority of individuals with autism spectrum disorder and Down syndrome belonged to Class 1 and the majority with CDKL5 deficiency disorder belonged to Class 3. Those with better functional abilities (verbal communication and independent walking were predominately members of Class 1 and those with frequent seizures were more often members of Class 2 and 3.

CONCLUSION

The profiles illustrated variation in QOL across a diverse group of children. QOL evaluations illustrate areas where interventions could improve QOL and provide advice to families as to where efforts may be best directed.

Expression of a Secretable, Cell-Penetrating CDKL5 Protein Enhances the Efficacy of Gene Therapy for CDKL5 Deficiency Disorder

Although delivery of a wild-type copy of the mutated gene to cells represents the most effective approach for a monogenic disease, proof-of-concept studies highlight significant efficacy caveats for treatment of brain disorders. Herein, we develop a cross-correction-based strategy to enhance the efficiency of a gene therapy for CDKL5 deficiency disorder, a severe neurodevelopmental disorder caused by CDKL5 gene mutations. We created a gene therapy vector that produces an Igk-TATk-CDKL5 fusion protein that can be secreted via constitutive secretory pathways and, due to the cell-penetration property of the TATk peptide, internalized by cells. We found that, although AAVPHP.B_Igk-TATk-CDKL5 and AAVPHP.B_CDKL5 vectors had similar brain infection efficiency, the AAVPHP.B_Igk-TATk-CDKL5 vector led to higher CDKL5 protein replacement due to secretion and penetration of the TATk-CDKL5 protein into the neighboring cells. Importantly, Cdkl5 KO mice treated with the AAVPHP.B_Igk-TATk-CDKL5 vector showed a behavioral and neuroanatomical improvement in comparison with vehicle or AAVPHP.B_CDKL5 vector-treated Cdkl5 KO mice. In conclusion, we provide the first evidence that a gene therapy based on a cross-correction approach is more effective at compensating Cdkl5-null brain defects than gene therapy based on the expression of the native CDKL5, opening avenues for the development of this innovative approach for other monogenic diseases.

Epilepsy Characteristics in Neurodevelopmental Disorders: Research from Patient Cohorts and Animal Models Focusing on Autism Spectrum Disorder

Epilepsy, a heterogeneous group of brain-related diseases, has continued to significantly burden society and families. Epilepsy comorbid with neurodevelopmental disorders (NDDs) is believed to occur due to multifaceted pathophysiological mechanisms involving disruptions in the excitation and inhibition (E/I) balance impeding widespread functional neuronal circuitry. Although the field has received much attention from the scientific community recently, the research has not yet translated into actionable therapeutics to completely cure epilepsy, particularly those comorbid with NDDs. In this review, we sought to elucidate the basic causes underlying epilepsy as well as those contributing to the association of epilepsy with NDDs. Comprehensive emphasis is put on some key neurodevelopmental genes implicated in epilepsy, such as MeCP2, SYNGAP1, FMR1, SHANK1-3 and TSC1, along with a few others, and the main electrophysiological and behavioral deficits are highlighted. For these genes, the progress made in developing appropriate and valid rodent models to accelerate basic research is also detailed. Further, we discuss the recent development in the therapeutic management of epilepsy and provide a briefing on the challenges and caveats in identifying and testing species-specific epilepsy models.

CDKL5 deficiency disorder: molecular insights and mechanisms of pathogenicity to fast-track therapeutic development

CDKL5 deficiency disorder (CDD) is an X-linked brain disorder of young children and is caused by pathogenic variants in the cyclin-dependent kinase-like 5 (CDKL5) gene. Individuals with CDD suffer infantile onset, drug-resistant seizures, severe neurodevelopmental impairment and profound lifelong disability. The CDKL5 protein is a kinase that regulates key phosphorylation events vital to the development of the complex neuronal network of the brain. Pathogenic variants identified in patients may either result in loss of CDKL5 catalytic activity or are hypomorphic leading to partial loss of function. Whilst the progressive nature of CDD provides an excellent opportunity for disease intervention, we cannot develop effective therapeutics without in-depth knowledge of CDKL5 function in human neurons. In this mini review, we summarize new findings on the function of CDKL5. These include CDKL5 phosphorylation targets and the consequence of disruptions on signaling pathways in the human brain. This new knowledge of CDKL5 biology may be leveraged to advance targeted drug discovery and rapid development of treatments for CDD. Continued development of effective humanized models will further propel our understanding of CDD biology and may permit the development and testing of therapies that will significantly alter CDD disease trajectory in young children.

Luteolin Treatment Ameliorates Brain Development and Behavioral Performance in a Mouse Model of CDKL5 Deficiency Disorder

CDKL5 deficiency disorder (CDD), a rare and severe neurodevelopmental disease caused by mutations in the X-linked CDKL5 gene, is characterized by early-onset epilepsy, intellectual disability, and autistic features. Although pharmacotherapy has shown promise in the CDD mouse model, safe and effective clinical treatments are still far off. Recently, we found increased microglial activation in the brain of a mouse model of CDD, the Cdkl5 KO mouse, suggesting that a neuroinflammatory state, known to be involved in brain maturation and neuronal dysfunctions, may contribute to the pathophysiology of CDD. The present study aims to evaluate the possible beneficial effect of treatment with luteolin, a natural flavonoid known to have anti-inflammatory and neuroprotective activities, on brain development and behavior in a heterozygous Cdkl5 (+/−) female mouse, the mouse model of CDD that best resembles the genetic clinical condition. We found that inhibition of neuroinflammation by chronic luteolin treatment ameliorates motor stereotypies, hyperactive profile and memory ability in Cdkl5 +/− mice. Luteolin treatment also increases hippocampal neurogenesis and improves dendritic spine maturation and dendritic arborization of hippocampal and cortical neurons. These findings show that microglia overactivation exerts a harmful action in the Cdkl5 +/− brain, suggesting that treatments aimed at counteracting the neuroinflammatory process should be considered as a promising adjuvant therapy for CDD.

Recommendations by the ClinGen Rett/Angelman-like expert panel for gene-specific variant interpretation methods

The genes MECP2, CDKL5, FOXG1, UBE3A, SLC9A6, and TCF4 present unique challenges for current ACMG/AMP variant interpretation guidelines. To address those challenges, the Rett and Angelman-like Disorders Variant Curation Expert Panel (Rett/AS VCEP) drafted gene-specific modifications. A pilot study was conducted to test the clarity and accuracy of using the customized variant interpretation criteria. Multiple curators obtained the same interpretation for 78 out of the 87 variants (~90%), indicating appropriate usage of the modified guidelines the majority of times by all the curators. The classification of 13 variants changed using these criteria specifications compared to when the variants were originally curated and as present in ClinVar. Many of these changes were due to internal data shared from laboratory members however some changes were because of changes in strength of criteria. There were no two-step classification changes and only 1 clinically relevant change (Likely pathogenic to VUS). The Rett/AS VCEP hopes that these gene-specific variant curation rules and the assertions provided help clinicians, clinical laboratories, and others interpret variants in these genes but also other fully penetrant, early-onset genes associated with rare disorders.

Development of an International Database for a Rare Genetic Disorder: The MECP2 Duplication Database (MDBase)

The natural history of MECP2 duplication syndrome (MDS), a rare X-linked neurodevelopmental disorder with an estimated birth prevalence of 1/150,000 live births, is poorly understood due to a lack of clinical data collected for research. Such information is critical to the understanding of disease progression, therapeutic endpoints and outcome measures for clinical trials, as well as the development of therapies and orphan products. This clinical information can be systematically collected from caregivers through data collation efforts—yet, no such database has existed for MDS before now. Here, in this methodological study, we document the development, launch and management of the international MECP2 Duplication Database (MDBase). The MDBase consists of an extensive family questionnaire that collects information on general medical history, system-specific health problems, medication and hospitalisation records, developmental milestones and function, and quality of life (for individuals with MDS, and their caregivers). Launched in 2020, in its first two years of operation the MDBase has collected clinical data from 154 individuals from 26 countries—the largest sample size to date. The success of this methodology for the establishment and operation of the MDBase may provide insight and aid in the development of databases for other rare neurodevelopmental disorders.

International Consensus Recommendations for the Assessment and Management of Individuals With CDKL5 Deficiency Disorder

CDKL5 Deficiency Disorder (CDD) is a rare, X-linked dominant condition that causes a developmental and epileptic encephalopathy (DEE). The incidence is between ~ 1:40,000 and 1:60,000 live births. Pathogenic variants in CDKL5 lead to seizures from infancy and severe neurodevelopmental delay. During infancy and childhood, individuals with CDD suffer impairments affecting cognitive, motor, visual, sleep, gastrointestinal and other functions. Here we present the recommendations of international healthcare professionals, experienced in CDD management, to address the multisystem and holistic needs of these individuals. Using a Delphi method, an anonymous survey was administered electronically to an international and multidisciplinary panel of expert clinicians and researchers. To provide summary recommendations, consensus was set, a priori, as >70% agreement for responses. In the absence of large, population-based studies to provide definitive evidence for treatment, we propose recommendations for clinical management, influenced by this proposed threshold for consensus. We believe these recommendations will help standardize, guide and improve the medical care received by individuals with CDD.

Cdkl5 mutant zebrafish shows skeletal and neuronal alterations mimicking human CDKL5 deficiency disorder

CDKL5 deficiency disorder (CDD) is a rare neurodevelopmental condition characterized primarily by seizures and impairment of cognitive and motor skills. Additional phenotypes include microcephaly, dysmorphic facial features, and scoliosis. Mutations in cyclin-dependent kinase-like 5 (CDKL5) gene, encoding a kinase essential for normal brain development and function, are responsible for CDD. Zebrafish is an accepted biomedical model for the study of several genetic diseases and has many advantages over other models. Therefore, this work aimed to characterize the phenotypic, behavioral, and molecular consequences of the Cdkl5 protein disruption in a cdkl5 mutant zebrafish line (sa21938). cdkl5sa21938 mutants displayed a reduced head size, suggesting microcephaly, a feature frequently observed in CDD individuals. Double staining revealed shorter craniofacial cartilage structures and decrease bone mineralization in cdkl5 homozygous zebrafish indicating an abnormal craniofacial cartilage development and impaired skeletal development. Motor behavior analysis showed that cdkl5sa21938 embryos had less frequency of double coiling suggesting impaired glutamatergic neurotransmission. Locomotor behavior analysis revealed that homozygous embryos swim shorter distances, indicative of impaired motor activity which is one of the main traits of CCD. Although no apparent spontaneous seizures were observed in these models, upon treatment with pentylenetetrazole, seizure behavior and an increase in the distance travelled were observed. Quantitative PCR showed that neuronal markers, including glutamatergic genes were dysregulated in cdkl5sa21938 mutant embryos. In conclusion, homozygous cdkl5sa21938 zebrafish mimic several characteristics of CDD, thus validating them as a suitable animal model to better understand the physiopathology of this disorder.

CDKL5 deficiency disorder: clinical features, diagnosis, and management

CDKL5 deficiency disorder (CDD) was first identified as a cause of human disease in 2004. Although initially considered a variant of Rett syndrome, CDD is now recognised as an independent disorder and classified as a developmental epileptic encephalopathy. It is characterised by early-onset (generally within the first 2 months of life) seizures that are usually refractory to polypharmacy. Development is severely impaired in patients with CDD, with only a quarter of girls and a smaller proportion of boys achieving independent walking; however, there is clinical variability, which is probably genetically determined. Gastrointestinal, sleep, and musculoskeletal problems are common in CDD, as in other developmental epileptic encephalopathies, but the prevalence of cerebral visual impairment appears higher in CDD. Clinicians diagnosing infants with CDD need to be familiar with the complexities of this disorder to provide appropriate counselling to the patients' families. Despite some benefit from ketogenic diets and vagal nerve stimulation, there has been little evidence that conventional antiseizure medications or their combinations are helpful in CDD, but further treatment trials are finally underway.

CDKL5 Deficiency Disorder-Related Epilepsy: A Review of Current and Emerging Treatment

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a developmental and epileptic encephalopathy with infantile-onset epilepsy. Most individuals with CDD develop refractory epilepsy with multiple seizure types. Management of seizures in CDD remains challenging for clinicians given the highly refractory nature of seizures and the limited number of disease-specific studies that offer a high level of evidence. Epileptic spasms are the most common seizure type in CDD and are more often refractory to standard first-line treatment than are spasms of other etiologies. In other seizure types, the effectiveness of antiseizure medications is limited and wanes over time. Ketogenic diet and palliative surgical treatments have both had mixed results in observational studies. When treating refractory seizures in CDD, we recommend carefully balancing seizure control and treatment-related side effects to optimize each individual's overall quality of life. Clinical trials of medications targeting epilepsy in CDD have been conducted, and additional investigational small molecules, gene therapy, and other disease-modifying therapies are in development for CDD.

ILAE classification and definition of epilepsy syndromes with onset in neonates and infants: Position statement by the ILAE Task Force on Nosology and Definitions

The International League Against Epilepsy (ILAE) Task Force on Nosology and Definitions proposes a classification and definition of epilepsy syndromes in the neonate and infant with seizure onset up to 2 years of age. The incidence of epilepsy is high in this age group and epilepsy is frequently associated with significant comorbidities and mortality. The licensing of syndrome specific antiseizure medications following randomized controlled trials and the development of precision, gene-related therapies are two of the drivers defining the electroclinical phenotypes of syndromes with onset in infancy. The principal aim of this proposal, consistent with the 2017 ILAE Classification of the Epilepsies, is to support epilepsy diagnosis and emphasize the importance of classifying epilepsy in an individual both by syndrome and etiology. For each syndrome, we report epidemiology, clinical course, seizure types, electroencephalography (EEG), neuroimaging, genetics, and differential diagnosis. Syndromes are separated into self-limited syndromes, where there is likely to be spontaneous remission and developmental and epileptic encephalopathies, diseases where there is developmental impairment related to both the underlying etiology independent of epileptiform activity and the epileptic encephalopathy. The emerging class of etiology-specific epilepsy syndromes, where there is a specific etiology for the epilepsy that is associated with a clearly defined, relatively uniform, and distinct clinical phenotype in most affected individuals as well as consistent EEG, neuroimaging, and/or genetic correlates, is presented. The number of etiology-defined syndromes will continue to increase, and these newly described syndromes will in time be incorporated into this classification. The tables summarize mandatory features, cautionary alerts, and exclusionary features for the common syndromes. Guidance is given on the criteria for syndrome diagnosis in resource-limited regions where laboratory confirmation, including EEG, MRI, and genetic testing, might not be available.

The Lived Experience of Parents' Receiving the Diagnosis of CDKL5 Deficiency Disorder for Their Child

CDKL5 deficiency disorder (CDD), a severe developmental and epileptic encephalopathy, is being diagnosed earlier with improved access to genetic testing, but this may also have unanticipated impacts on parents' experience receiving the diagnosis. This study explores the lived experience of parents receiving a diagnosis of CDD for their child using mixed methods. Thirty-seven semistructured interviews were conducted with parents of children with a diagnosis of CDD, which were coded and analyzed to identify themes. Grief was a nearly universal theme expressed among participants. Parents of younger children discussed grief in the context of receiving the diagnosis, whereas parents of older children indicated they were at different stages along the grieving journey when they received the diagnosis. Parents with less understanding of their child's prognosis (poorer prognostic awareness) connected their grief to receiving the diagnosis as this brought a clear understanding of the prognosis. Several themes suggested what providers did well to improve the diagnostic experience for parents, much of which aligns with existing literature around how to provide serious news. Additionally, parents identified long-term benefits of having a diagnosis for their child's medical problems. Although interview data were concordant with a survey of parents' diagnostic experience from a large international cohort, most participants in this study were relatively affluent, white mothers and further research is needed to better understand if other groups of parents have a different diagnostic experience. This study gives context of parental experience that providers should be aware of when conveying new genetic diagnoses to families.