Adult-onset epilepsy and hippocampal pathology in a California sea lion (Zalophus californianus): A case study of suspected in utero exposure to domoic acid.

Domoic acid (DA) is a naturally occurring marine neurotoxin produced by Pseudo-nitzschia diatoms. Adult California sea lions (Zalophus californianus) can experience multiple post-exposure syndromes, including acute toxicosis and chronic epilepsy. Additionally, a delayed-onset epileptic syndrome is proposed for California sea lions (CSL) exposed in utero. This brief report explores a case of a CSL developing adult-onset epilepsy with progressive hippocampal neuropathology. Initial brain magnetic resonance imaging (MRI) and hippocampal volumetric analyses relative to brain size were normal. Approximately 7 years later, MRI studies to evaluate a newly developed epileptic syndrome demonstrated unilateral hippocampal atrophy. While other causes of unilateral hippocampal atrophy cannot be completely excluded, this case may represent in vivo evidence of adult-onset epileptiform DA toxicosis in a CSL. By estimating in utero DA exposure time period, and extrapolating from studies conducted on laboratory species, this case provides circumstantial evidence for a neurodevelopmental explanation correlating in utero exposure to adult-onset disease. Evidence of delayed disease development secondary to gestational exposure to naturally occurring DA has broad implications for marine mammal medicine and public health.

Neurosurgery in feline epilepsy, including clinicopathology of feline epilepsy syndromes.

Feline epilepsy is treated with antiseizure medications, which achieves fair to good seizure control. However, a small subset of feline patients with drug-resistant epilepsy requires alternative therapies. Furthermore, approximately 50 % of cats with epileptic seizures are diagnosed with structural epilepsy with or without hippocampal abnormality and may respond to surgical intervention. The presence of hippocampal pathology and intracranial tumors is a key point to consider for surgical treatment. This review describes feline epilepsy syndrome and epilepsy-related pathology, and discusses the indications for and availability of neurosurgery, including lesionectomy, temporal lobectomy with hippocampectomy, and corpus callosotomy, for cats with different epilepsy types.

Spontaneous seizure and memory loss in mice expressing an epileptic encephalopathy variant in the calmodulin-binding domain of Kv7.2.

Epileptic encephalopathy (EE) is characterized by seizures that respond poorly to antiseizure drugs, psychomotor delay, and cognitive and behavioral impairments. One of the frequently mutated genes in EE is KCNQ2, which encodes the Kv7.2 subunit of voltage-gated Kv7 potassium channels. Kv7 channels composed of Kv7.2 and Kv7.3 are enriched at the axonal surface, where they potently suppress neuronal excitability. Previously, we reported that the de novo dominant EE mutation M546V in human Kv7.2 blocks calmodulin binding to Kv7.2 and axonal surface expression of Kv7 channels via their intracellular retention. However, whether these pathogenic mechanisms underlie epileptic seizures and behavioral comorbidities remains unknown. Here, we report conditional transgenic cKcnq2+/M547V mice, in which expression of mouse Kv7.2-M547V (equivalent to human Kv7.2-M546V) is induced in forebrain excitatory pyramidal neurons and astrocytes. These mice display early mortality, spontaneous seizures, enhanced seizure susceptibility, memory impairment, and repetitive behaviors. Furthermore, hippocampal pathology shows widespread neurodegeneration and reactive astrocytes. This study demonstrates that the impairment in axonal surface expression of Kv7 channels is associated with epileptic seizures, cognitive and behavioral deficits, and neuronal loss in KCNQ2-related EE.

CDKL5 kinase controls transcription-coupled responses to DNA damage.

Mutations in the gene encoding the CDKL5 kinase are among the most common genetic causes of childhood epilepsy and can also give rise to the severe neurodevelopmental condition CDD (CDKL5 deficiency disorder). Despite its importance for human health, the phosphorylation targets and cellular roles of CDKL5 are poorly understood, especially in the cell nucleus. Here, we report that CDKL5 is recruited to sites of DNA damage in actively transcribed regions of the nucleus. A quantitative phosphoproteomic screen for nuclear CDKL5 substrates reveals a network of transcriptional regulators including Elongin A (ELOA), phosphorylated on a specific CDKL5 consensus motif. Recruitment of CDKL5 and ELOA to damaged DNA, and subsequent phosphorylation of ELOA, requires both active transcription and the synthesis of poly(ADP-ribose) (PAR), to which CDKL5 can bind. Critically, CDKL5 kinase activity is essential for the transcriptional silencing of genes induced by DNA double-strand breaks. Thus, CDKL5 is a DNA damage-sensing, PAR-controlled transcriptional modulator, a finding with implications for understanding the molecular basis of CDKL5-related diseases.

Brain morphological abnormalities in children with cyclin-dependent kinase-like 5 deficiency disorder.

BACKGROUND: To quantitatively evaluate the brain MRI morphological abnormalities in patients with cyclin-dependent kinase-like 5 deficiency disorder (CDD) on a group level and longitudinally. METHODS: We performed surface-based MRI analysis on high-resolution T1-weighted images on three CDD patients scanned at age of three years, and compared with 12 age- and gender-matched healthy controls. We further examined the longitudinal morphological changes in one patient with a follow-up of 5 years. RESULTS: CDD patients presented significant reductions in total intracranial volume, total gray matter (GM) volume and subcortical GM volume compared to controls. For subcortical regions, significant GM volume reductions were seen in the brain stem, bilateral thalamus, bilateral hippocampus, bilateral cerebellum and left amygdala. Although GM volume of cortical mantle did not show statistical differences overall, significant reduction was detected in bilateral parietal, left occipital and right temporal lobes. Cortical thickness exhibited significant decreases in bilateral occipital, parietal and temporal lobes, while surface area did not show any significant differences. Longitudinal follow-up in one patient revealed a monotonic downward trend of relative volume in the majority of brain regions. The relative surface area appeared to gain age-related growth, whereas the relative cortical thickness exhibited a striking progressive decline over time. CONCLUSIONS: Quantitative morphology analysis in children with CDD showed global volume loss in the cortex and more notably in the subcortical gray matter, with a progressive trend along with the disease course. Cortical thickness is a more sensitive measure to disclose cortical atrophy and disease progression than surface area.

In vivo magnetic resonance spectroscopy in the brain of Cdkl5 null mice reveals a metabolic profile indicative of mitochondrial dysfunctions.

Mutations in the X-linked CDKL5 gene cause CDKL5 deficiency disorder (CDD), a severe neurodevelopmental condition mainly characterized by infantile epileptic encephalopathy, intellectual disability, and autistic features. The molecular mechanisms underlying the clinical symptoms remain largely unknown and the identification of reliable biomarkers in animal models will certainly contribute to increase our comprehension of CDD as well as to assess the efficacy of therapeutic strategies. Here, we used different Magnetic Resonance (MR) methods to disclose structural, functional, or metabolic signatures of Cdkl5 deficiency in the brain of adult mice. We found that loss of Cdkl5 does not cause cerebral atrophy but affects distinct brain areas, particularly the hippocampus. By in vivo proton-MR spectroscopy (MRS), we revealed in the Cdkl5 null brain a metabolic dysregulation indicative of mitochondrial dysfunctions. Accordingly, we unveiled a significant reduction in ATP levels and a decrease in the expression of complex IV of mitochondrial electron transport chain. Conversely, the number of mitochondria appeared preserved. Importantly, we reported a significant defect in the activation of one of the major regulators of cellular energy balance, the adenosine monophosphate-activated protein kinase (AMPK), that might contribute to the observed metabolic impairment and become an interesting therapeutic target for future preclinical trials. In conclusion, MRS revealed in the Cdkl5 null brain the presence of a metabolic dysregulation suggestive of a mitochondrial dysfunction that permitted to foster our comprehension of Cdkl5 deficiency and brought our interest towards targeting mitochondria as therapeutic strategy for CDD.

Exploring genotype-phenotype relationships in the CDKL5 deficiency disorder using an international dataset.

Characterized by early-onset seizures, global developmental delay and severe motor deficits, CDKL5 deficiency disorder is caused by pathogenic variants in the cyclin-dependent kinase-like 5 gene. Previous efforts to investigate genotype-phenotype relationships have been limited due to small numbers of recurrent mutations and small cohort sizes. Using data from the International CDKL5 Disorder Database we examined genotype-phenotype relationships for 13 recurrent CDKL5 variants and the previously analyzed historic variant groupings. We have applied the CDKL5 Developmental Score (CDS) and an adapted version of the CDKL5 Clinical Severity Assessment (CCSA), to grade the severity of phenotype and developmental outcomes for 285 individuals with CDKL5 variants. Comparisons of adapted CCSA and CDS between recurrent variants and variant groups were performed using multiple linear regression adjusting for age and sex. Individuals with the missense variant, p.Arg178Trp, had the highest mean adapted CCSA and lowest mean developmental scores. Other variants producing severe phenotypes included p.Arg559* and p.Arg178Gln. Variants producing milder phenotypes included p.Arg134*, p.Arg550*, and p.Glu55Argfs*20. There are observed differences in phenotype severity and developmental outcomes for individuals with different CDKL5 variants. However, the historic variant groupings did not seem to reflect differences in phenotype severity or developmental outcomes as clearly as analyzed by individual variants.

Cortico-striato-thalamo-cerebellar networks of structural covariance underlying different epilepsy syndromes associated with generalized tonic-clonic seizures.

Generalized tonic-clonic seizures (GTCS) are the severest and most remarkable clinical expressions of human epilepsy. Cortical, subcortical, and cerebellar structures, organized with different network patterns, underlying the pathophysiological substrates of genetic associated epilepsy with GTCS (GE-GTCS) and focal epilepsy associated with focal to bilateral tonic-clonic seizure (FE-FBTS). Structural covariance analysis can delineate the features of epilepsy network related with long-term effects from seizure. Morphometric MRI data of 111 patients with GE-GTCS, 111 patients with FE-FBTS and 111 healthy controls were studied. Cortico-striato-thalao-cerebellar networks of structural covariance within the gray matter were constructed using a Winner-take-all strategy with five cortical parcellations. Comparisons of structural covariance networks were conducted using permutation tests, and module effects of disease duration on networks were conducted using GLM model. Both patient groups showed increased connectivity of structural covariance relative to controls, mainly within the striatum and thalamus, and mostly correlated with the frontal, motor, and somatosensory cortices. Connectivity changes increased as a function of epilepsy durations. FE-FBTS showed more intensive and extensive gray matter changes with volumetric loss and connectivity increment than GE-GTCS. Our findings implicated cortico-striato-thalamo-cerebellar network changes at a large temporal scale in GTCS, with FE-FBTS showing more severe network disruption. The study contributed novel imaging evidence for understanding the different epilepsy syndromes associated with generalized seizures.

White matter abnormalities across different epilepsy syndromes in adults: an ENIGMA-Epilepsy study.

The epilepsies are commonly accompanied by widespread abnormalities in cerebral white matter. ENIGMA-Epilepsy is a large quantitative brain imaging consortium, aggregating data to investigate patterns of neuroimaging abnormalities in common epilepsy syndromes, including temporal lobe epilepsy, extratemporal epilepsy, and genetic generalized epilepsy. Our goal was to rank the most robust white matter microstructural differences across and within syndromes in a multicentre sample of adult epilepsy patients. Diffusion-weighted MRI data were analysed from 1069 healthy controls and 1249 patients: temporal lobe epilepsy with hippocampal sclerosis (n = 599), temporal lobe epilepsy with normal MRI (n = 275), genetic generalized epilepsy (n = 182) and non-lesional extratemporal epilepsy (n = 193). A harmonized protocol using tract-based spatial statistics was used to derive skeletonized maps of fractional anisotropy and mean diffusivity for each participant, and fibre tracts were segmented using a diffusion MRI atlas. Data were harmonized to correct for scanner-specific variations in diffusion measures using a batch-effect correction tool (ComBat). Analyses of covariance, adjusting for age and sex, examined differences between each epilepsy syndrome and controls for each white matter tract (Bonferroni corrected at P < 0.001). Across 'all epilepsies' lower fractional anisotropy was observed in most fibre tracts with small to medium effect sizes, especially in the corpus callosum, cingulum and external capsule. There were also less robust increases in mean diffusivity. Syndrome-specific fractional anisotropy and mean diffusivity differences were most pronounced in patients with hippocampal sclerosis in the ipsilateral parahippocampal cingulum and external capsule, with smaller effects across most other tracts. Individuals with temporal lobe epilepsy and normal MRI showed a similar pattern of greater ipsilateral than contralateral abnormalities, but less marked than those in patients with hippocampal sclerosis. Patients with generalized and extratemporal epilepsies had pronounced reductions in fractional anisotropy in the corpus callosum, corona radiata and external capsule, and increased mean diffusivity of the anterior corona radiata. Earlier age of seizure onset and longer disease duration were associated with a greater extent of diffusion abnormalities in patients with hippocampal sclerosis. We demonstrate microstructural abnormalities across major association, commissural, and projection fibres in a large multicentre study of epilepsy. Overall, patients with epilepsy showed white matter abnormalities in the corpus callosum, cingulum and external capsule, with differing severity across epilepsy syndromes. These data further define the spectrum of white matter abnormalities in common epilepsy syndromes, yielding more detailed insights into pathological substrates that may explain cognitive and psychiatric co-morbidities and be used to guide biomarker studies of treatment outcomes and/or genetic research.

Dopaminergic loss of cyclin-dependent kinase-like 5 recapitulates methylphenidate-remediable hyperlocomotion in mouse model of CDKL5 deficiency disorder.

Cyclin-dependent kinase-like 5 (CDKL5), a serine-threonine kinase encoded by an X-linked gene, is highly expressed in the mammalian forebrain. Mutations in this gene cause CDKL5 deficiency disorder, a neurodevelopmental encephalopathy characterized by early-onset seizures, motor dysfunction, and intellectual disability. We previously found that mice lacking CDKL5 exhibit hyperlocomotion and increased impulsivity, resembling the core symptoms in attention-deficit hyperactivity disorder (ADHD). Here, we report the potential neural mechanisms and treatment for hyperlocomotion induced by CDKL5 deficiency. Our results showed that loss of CDKL5 decreases the proportion of phosphorylated dopamine transporter (DAT) in the rostral striatum, leading to increased levels of extracellular dopamine and hyperlocomotion. Administration of methylphenidate (MPH), a DAT inhibitor clinically effective to improve symptoms in ADHD, significantly alleviated the hyperlocomotion phenotype in Cdkl5 null mice. In addition, the improved behavioral effects of MPH were accompanied by a region-specific restoration of phosphorylated dopamine- and cAMP-regulated phosphoprotein Mr 32 kDa, a key signaling protein for striatal motor output. Finally, mice carrying a Cdkl5 deletion selectively in DAT-expressing dopaminergic neurons, but not dopamine receptive neurons, recapitulated the hyperlocomotion phenotype found in Cdkl5 null mice. Our findings suggest that CDKL5 is essential to control locomotor behavior by regulating region-specific dopamine content and phosphorylation of dopamine signaling proteins in the striatum. The direct, as well as indirect, target proteins regulated by CDKL5 may play a key role in movement control and the therapeutic development for hyperactivity disorders.

Novel Dominant KCNQ2 Exon 7 Partial In-Frame Duplication in a Complex Epileptic and Neurodevelopmental Delay Syndrome.

Complex neurodevelopmental syndromes frequently have an unknown etiology, in which genetic factors play a pathogenic role. This study utilizes whole-exome sequencing (WES) to examine four members of a family with a son presenting, since birth, with epileptic-like crises, combined with cerebral palsy, severe neuromotor and developmental delay, dystonic tetraparexia, axonal motor affectation, and hyper-excitability of unknown origin. The WES study detected within the patient a de novo heterozygous in-frame duplication of thirty-six nucleotides within exon 7 of the human KCNQ2 gene. This insertion duplicates the first twelve amino acids of the calmodulin binding site I. Molecular dynamics simulations of this KCNQ2 peptide duplication, modelled on the 3D structure of the KCNQ2 protein, suggest that the duplication may lead to the dysregulation of calcium inhibition of this protein function.

RNAi-Based Gene Therapy Rescues Developmental and Epileptic Encephalopathy in a Genetic Mouse Model.

Developmental and epileptic encephalopathy (DEE) associated with de novo variants in the gene encoding dynamin-1 (DNM1) is a severe debilitating disease with no pharmacological remedy. Like most genetic DEEs, the majority of DNM1 patients suffer from therapy-resistant seizures and comorbidities such as intellectual disability, developmental delay, and hypotonia. We tested RNAi gene therapy in the Dnm1 fitful mouse model of DEE using a Dnm1-targeted therapeutic microRNA delivered by a self-complementary adeno-associated virus vector. Untreated or control-injected fitful mice have growth delay, severe ataxia, and lethal tonic-clonic seizures by 3 weeks of age. These major impairments are mitigated following a single treatment in newborn mice, along with key underlying cellular features including gliosis, cell death, and aberrant neuronal metabolic activity typically associated with recurrent seizures. Our results underscore the potential for RNAi gene therapy to treat DNM1 disease and other genetic DEEs where treatment would require inhibition of the pathogenic gene product.

X-Linked Familial Focal Epilepsy Associated With Xp22.31 Deletion.

BACKGROUND: The genetic basis for familial focal epilepsy is poorly understood, with most of the known genetic causes occurring via autosomal dominant inheritance. X-linked familial focal epilepsy has not been previously reported. METHODS: We reviewed our research database for cases of X-linked focal epilepsy. RESULTS: We identified three boys with X-linked ichthyosis and focal epilepsy, including two maternal cousins. Age of seizure onset ranged from seven to 10 years, and all three patients had seizures that were relatively easily controlled. The epilepsy phenotype in all boys was consistent with self-limited focal epilepsy of childhood, most closely resembling childhood epilepsy with centrotemporal spikes. Brain magnetic resonance imaging was normal in two of the boys, with a third found to have a suspected focal cortical dysplasia. All three boys carried maternally inherited hemizygous Xp22.31 deletions (estimated size 0.9 to 1.66 Mb), affecting four to six genes. Of the affected genes, only STS has clear clinical relevance; deletions, and pathogenic variants in STS cause X-linked ichthyosis, although all patients described had only minor skin findings. CONCLUSIONS: The findings in these patients illustrate that X-linked familial focal epilepsy can occur, although it is a rare entity. Although STS pathogenic variants are likely better categorized as an epilepsy risk factor, variants in this gene may partially explain the male predominance observed in specific epilepsy phenotypes, namely childhood epilepsy with centrotemporal spikes.

Bi-allelic GAD1 variants cause a neonatal onset syndromic developmental and epileptic encephalopathy.

Developmental and epileptic encephalopathies are a heterogeneous group of early-onset epilepsy syndromes dramatically impairing neurodevelopment. Modern genomic technologies have revealed a number of monogenic origins and opened the door to therapeutic hopes. Here we describe a new syndromic developmental and epileptic encephalopathy caused by bi-allelic loss-of-function variants in GAD1, as presented by 11 patients from six independent consanguineous families. Seizure onset occurred in the first 2 months of life in all patients. All 10 patients, from whom early disease history was available, presented with seizure onset in the first month of life, mainly consisting of epileptic spasms or myoclonic seizures. Early EEG showed suppression-burst or pattern of burst attenuation or hypsarrhythmia if only recorded in the post-neonatal period. Eight patients had joint contractures and/or pes equinovarus. Seven patients presented a cleft palate and two also had an omphalocele, reproducing the phenotype of the knockout Gad1-/- mouse model. Four patients died before 4 years of age. GAD1 encodes the glutamate decarboxylase enzyme GAD67, a critical actor of the γ-aminobutyric acid (GABA) metabolism as it catalyses the decarboxylation of glutamic acid to form GABA. Our findings evoke a novel syndrome related to GAD67 deficiency, characterized by the unique association of developmental and epileptic encephalopathies, cleft palate, joint contractures and/or omphalocele.

Modifier genes in SCN1A-related epilepsy syndromes.

BACKGROUND: SCN1A is one of the most important epilepsy-related genes, with pathogenic variants leading to a range of phenotypes with varying disease severity. Different modifying factors have been hypothesized to influence SCN1A-related phenotypes. We investigate the presence of rare and more common variants in epilepsy-related genes as potential modifiers of SCN1A-related disease severity. METHODS: 87 patients with SCN1A-related epilepsy were investigated. Whole-exome sequencing was performed by the Beijing Genomics Institute (BGI). Functional variants in 422 genes associated with epilepsy and/or neuronal excitability were investigated. Differences in proportions of variants between the epilepsy genes and four control gene sets were calculated, and compared to the proportions of variants in the same genes in the ExAC database. RESULTS: Statistically significant excesses of variants in epilepsy genes were observed in the complete cohort and in the combined group of mildly and severely affected patients, particularly for variants with minor allele frequencies of <0.05. Patients with extreme phenotypes showed much greater excesses of epilepsy gene variants than patients with intermediate phenotypes. CONCLUSION: Our results indicate that relatively common variants in epilepsy genes, which would not necessarily be classified as pathogenic, may play a large role in modulating SCN1A phenotypes. They may modify the phenotypes of both severely and mildly affected patients. Our results may be a first step toward meaningful testing of modifier gene variants in regular diagnostics for individual patients, to provide a better estimation of disease severity for newly diagnosed patients.

Increased DNA Damage and Apoptosis in CDKL5-Deficient Neurons.

Mutations in the CDKL5 gene, which encodes a serine/threonine kinase, causes a rare encephalopathy, characterized by early-onset epilepsy and severe intellectual disability, named CDKL5 deficiency disorder (CDD). In vitro and in vivo studies in mouse models of Cdkl5 deficiency have highlighted the role of CDKL5 in brain development and, in particular, in the morphogenesis and synaptic connectivity of hippocampal and cortical neurons. Interestingly, Cdkl5 deficiency in mice increases vulnerability to excitotoxic stress in hippocampal neurons. However, the mechanism by which CDKL5 controls neuronal survival is far from being understood. To investigate further the function of CDKL5 and dissect the molecular mechanisms underlying neuronal survival, we generated a human neuronal model of CDKL5 deficiency, using CRISPR/Cas9-mediated genome editing. We demonstrated that CDKL5 deletion in human neuroblastoma SH-SY5Y cells not only impairs neuronal maturation but also reduces cell proliferation and survival, with alterations in the AKT and ERK signaling pathways and an increase in the proapoptotic BAX protein and in DNA damage-associated biomarkers (i.e., γH2AX, RAD50, and PARP1). Furthermore, CDKL5-deficient cells were hypersensitive to DNA damage-associated stress, accumulated more DNA damage foci (γH2AX positive) and were more prone to cell death than the controls. Importantly, increased kainic acid-induced cell death of hippocampal neurons of Cdkl5 KO mice correlated with an increased γH2AX immunostaining. The results suggest a previously unknown role for CDKL5 in DNA damage response that could underlie the pro-survival function of CDKL5.

Expanding the genotype-phenotype correlation of de novo heterozygous missense variants in YWHAG as a cause of developmental and epileptic encephalopathy.

Developmental and Epileptic encephalopathies (DEE) describe heterogeneous epilepsy syndromes, characterized by early-onset, refractory seizures and developmental delay (DD). Several DEE associated genes have been reported. With increased access to whole exome sequencing (WES), new candidate genes are being identified although there are fewer large cohort papers describing the clinical phenotype in such patients. We describe 6 unreported individuals and provide updated information on an additional previously reported individual with heterozygous de novo missense variants in YWHAG. We describe a syndromal phenotype, report 5 novel, and a recurrent p.Arg132Cys YWHAG variant and compare developmental trajectory and treatment strategies in this cohort. We provide further evidence of causality in YWHAG variants. WES was performed in five patients via Deciphering Developmental Disorders Study and the remaining two were identified via Genematcher and AnnEX databases. De novo variants identified from exome data were validated using Sanger sequencing. Seven out of seven patients in the cohort have de novo, heterozygous missense variants in YWHAG including 2/7 patients with a recurrent c.394C > T, p.Arg132Cys variant; 1/7 has a second, pathogenic variant in STAG1. Characteristic features included: early-onset seizures, predominantly generalized tonic-clonic and absence type (7/7) with good response to standard anti-epileptic medications; moderate DD; Intellectual Disability (ID) (5/7) and Autism Spectrum Disorder (3/7). De novo YWHAG missense variants cause EE, characterized by early-onset epilepsy, ID and DD, supporting the hypothesis that YWHAG loss-of-function causes a neurological phenotype. Although the exact mechanism of disease resulting from alterations in YWHAG is not fully known, it is possible that haploinsufficiency of YWHAG in developing cerebral cortex may lead to abnormal neuronal migration resulting in DEE.

Altered NMDAR signaling underlies autistic-like features in mouse models of CDKL5 deficiency disorder.

CDKL5 deficiency disorder (CDD) is characterized by epilepsy, intellectual disability, and autistic features, and CDKL5-deficient mice exhibit a constellation of behavioral phenotypes reminiscent of the human disorder. We previously found that CDKL5 dysfunction in forebrain glutamatergic neurons results in deficits in learning and memory. However, the pathogenic origin of the autistic features of CDD remains unknown. Here, we find that selective loss of CDKL5 in GABAergic neurons leads to autistic-like phenotypes in mice accompanied by excessive glutamatergic transmission, hyperexcitability, and increased levels of postsynaptic NMDA receptors. Acute, low-dose inhibition of NMDAR signaling ameliorates autistic-like behaviors in GABAergic knockout mice, as well as a novel mouse model bearing a CDD-associated nonsense mutation, CDKL5 R59X, implicating the translational potential of this mechanism. Together, our findings suggest that enhanced NMDAR signaling and circuit hyperexcitability underlie autistic-like features in mouse models of CDD and provide a new therapeutic avenue to treat CDD-related symptoms.

Cyclin-Dependent Kinase-Like 5 Deficiency Disorder: Clinical Review.

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is a developmental encephalopathy caused by pathogenic variants in the gene CDKL5. This unique disorder includes early infantile onset refractory epilepsy, hypotonia, developmental intellectual and motor disabilities, and cortical visual impairment. We review the clinical presentations and genetic variations in CDD based on a systematic literature review and experience in the CDKL5 Centers of Excellence. We propose minimum diagnostic criteria. Pathogenic variants include deletions, truncations, splice variants, and missense variants. Pathogenic missense variants occur exclusively within the kinase domain or affect splice sites. The CDKL5 protein is widely expressed in the brain, predominantly in neurons, with roles in cell proliferation, neuronal migration, axonal outgrowth, dendritic morphogenesis, and synapse development. The molecular biology of CDD is revealing opportunities in precision therapy, with phase 2 and 3 clinical trials underway or planned to assess disease specific and disease modifying treatments.