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CDKL5

CDKL5, or cyclin-dependent kinase-like 5, is a gene located on the X chromosome that encodes a serine/threonine kinase protein crucial for neuronal development, including processes such as neuron maturation, migration, and synaptic function in the brain.^[1] Pathogenic variants in the CDKL5 gene lead to CDKL5 deficiency disorder (CDD), a rare X-linked dominant developmental and epileptic encephalopathy characterized by severe, early-onset intractable epilepsy typically beginning in infancy, profound developmental delays, and intellectual disability.^[2]^[3] CDD primarily affects females, with an estimated incidence of 1 in 40,000 to 60,000 newborns, though males can also be impacted, often more severely due to hemizygosity; females outnumber males at a ratio of approximately 4:1.^[3]^[2] The disorder was initially classified as an atypical form of Rett syndrome but is now recognized as a distinct condition resulting from insufficient or nonfunctional CDKL5 protein, which disrupts brain development and function.^[3] Over 250 different mutations have been identified as of 2024, most commonly de novo (not inherited from parents) and affecting the kinase domain of the protein, leading to a loss of enzymatic activity.^[1]^[4] Inheritance follows an X-linked dominant pattern, with skewed X-chromosome inactivation in females influencing phenotypic severity; in males, variants cause profound symptoms due to hemizygosity.^[2] Clinically, CDD manifests with seizures in over 99% of individuals, often starting within the first few weeks of life and resistant to standard antiepileptic drugs, alongside 100% prevalence of severe developmental delays.^[2] Other hallmark features include severe cognitive impairment with limited or absent speech, gross and fine motor delays (e.g., inability to walk independently in most cases), visual impairments such as cortical visual impairment in about 80% of patients, and frequent comorbidities like sleep disturbances (90%), gastrointestinal issues, and scoliosis.^[2]^[3] Some individuals exhibit hand stereotypies, autonomic dysfunction, and distinctive facial features, though the phenotype can vary based on mutation type and genetic modifiers.^[3] Diagnosis is confirmed through molecular genetic testing, such as targeted sequencing of the CDKL5 gene or epilepsy gene panels, often prompted by clinical suspicion in infants with refractory epilepsy and neurodevelopmental delays.^[2] Management is supportive and multidisciplinary, focusing on seizure control with therapies like ganaxolone (Ztalmy®) approved for children aged 2 years and older, physical and occupational therapy, nutritional support, and behavioral interventions; no curative treatment exists, but ongoing research explores gene therapy and kinase activators.^[2] Early diagnosis and intervention are critical to optimizing quality of life, with surveillance guidelines recommending regular assessments for epilepsy, vision, sleep, and orthopedic issues.^[2]

Genetics and Genomics

Gene Location and Expression

The CDKL5 gene is located on the short arm of the X chromosome at cytogenetic band Xp22.13.^[5] It spans approximately 228 kb of genomic DNA and consists of 24 exons, with the first three (exons 1, 1a, and 1b) being untranslated and the remaining 21 containing the coding sequence.^[6]^[7] Alternative splicing of the CDKL5 pre-mRNA generates multiple transcript isoforms, with at least five identified in humans.^[8] The predominant isoform in the brain, CDKL5_1 (also known as hCDKL5_1), is the full-length transcript of approximately 9.7 kb that includes all coding exons and a large 3' untranslated region, encoding a 1030-amino-acid protein.^[8]^[9] Another notable isoform, CDKL5_2, results from the inclusion of an alternative exon (exon 17 or 16b in varying nomenclatures) that adds 41 amino acids to the C-terminal region, while maintaining the overall reading frame; this isoform constitutes about 10% of brain transcripts and shows similar widespread expression.^[8]^[10] CDKL5 expression is highly tissue-specific, with the highest levels observed in the brain—particularly in forebrain structures such as the cerebral cortex, hippocampus, striatum, and olfactory bulb—compared to low expression in other tissues like liver, lung, and heart.^[11]^[12] During development, CDKL5 mRNA and protein levels are low in embryonic and fetal stages but undergo significant upregulation, peaking in early postnatal periods before stabilizing at high levels in the adult brain.^[13]^[14] Brain-specific transcription of CDKL5 is regulated by multiple promoters and enhancers. The gene features two primary transcription start sites (TSSs), p1@CDKL5 (broad promoter within a CpG island) and p2@CDKL5 (sharp promoter), both active in neural tissues and associated with high expression in cortical and hippocampal regions.^[14] Enhancers, marked by histone modifications like H3K27ac, partially overlap promoter regions and correlate with neuron-enriched expression profiles, contributing to the developmental and regional specificity observed.^[14]

Pathogenic Variants

Pathogenic variants in the CDKL5 gene, located on the X chromosome at Xp22.13, are the primary cause of CDKL5 deficiency disorder (CDD), an X-linked dominant neurodevelopmental condition. These variants disrupt the function of the cyclin-dependent kinase-like 5 protein, leading to severe developmental and epileptic encephalopathy. The spectrum of pathogenic variants is diverse, with the majority resulting in loss-of-function effects that severely impair neuronal development.^[2] The predominant mutation types include truncating variants such as nonsense and frameshift mutations, which account for approximately 70% of reported cases and introduce premature termination codons leading to protein truncation or absence. Missense variants comprise about 20% of pathogenic changes, often affecting critical residues in the protein's functional domains, while large deletions or duplications make up the remaining proportion, typically detected in around 16% of cases via targeted analysis. Splice site variants are also noted, contributing to aberrant RNA processing. As of 2025, databases like ClinVar document over 500 distinct pathogenic or likely pathogenic variants in CDKL5, reflecting the genetic heterogeneity of the disorder.^[15]^[2]^[16] Mutation hotspots are concentrated in the catalytic domain encoded by exons 4-11, where missense variants frequently cluster and disrupt kinase activity, underscoring the region's functional importance. Nearly all pathogenic variants (approximately 99%) arise de novo, with rare instances of inheritance from heterozygous or mosaic mothers following X-linked patterns; affected males often exhibit mosaicism due to the gene's X-linked location, which can result in variable expressivity. The estimated prevalence of CDD is about 1 in 40,000 females, with an overall incidence of 2.36 per 100,000 live births.^[15]^[2]^[16] At the genetic level, truncating variants commonly trigger nonsense-mediated decay (NMD), substantially reducing CDKL5 mRNA levels and yielding little to no functional protein. Other impacts include exon skipping or altered splicing, which can produce truncated or unstable proteins lacking essential domains. These molecular consequences lead to haploinsufficiency in females and more profound loss in mosaic males, directly contributing to the disorder's pathogenesis without compensatory mechanisms from the wild-type allele.^[2]^[15]

Protein Characteristics

Structural Domains

The CDKL5 protein is a large serine/threonine kinase comprising approximately 1,030 amino acids and exhibiting a molecular weight of about 115 kDa.^[17] Its architecture is characterized by a bipartite organization, with a highly conserved N-terminal kinase domain and an extended C-terminal regulatory region that modulates localization and interactions.^[18] The N-terminal kinase domain spans residues 1–272 and shares significant homology with cyclin-dependent kinases (CDKs), enabling ATP-dependent phosphorylation.^[19] Within this domain, key conserved motifs include the ATP-binding P-loop (GXGXXG motif, residues 14–19), which facilitates nucleotide binding, and the activation loop featuring a TEY motif at residues 169–171, which is critical for catalytic activation through autophosphorylation.^[18]^[20] The C-terminal region (residues 273–1,030) is largely unstructured and encompasses functional elements such as a nuclear localization signal (NLS) that promotes nuclear import, a proline-rich domain rich in PXXP motifs for scaffolding protein-protein interactions, and multiple regulatory phosphorylation sites that fine-tune protein dynamics.^[20]^[21] Post-translational modifications in this region, including ubiquitination sites targeted by the E3 ligase Mind Bomb 1 (Mib1), regulate CDKL5 stability by promoting proteasomal degradation.^[22] Alternative splicing of the CDKL5 gene produces multiple isoforms that retain the core kinase domain but exhibit variations in C-terminal composition, potentially altering regulatory features and tissue-specific expression.^[23]

Kinase Activity

CDKL5 functions as a serine/threonine protein kinase, catalyzing the transfer of phosphate groups from ATP to serine or threonine residues on target substrates, with a strong preference for motifs containing an arginine-proline dipeptide preceding the phosphorylatable residue (consensus: RPXS/T, where X is any amino acid).^[24] In vitro kinase assays using recombinant CDKL5 have confirmed its ability to autophosphorylate at multiple sites within the activation loop, including Thr169 and Tyr171 of the conserved TEY motif (residues 169–171), an event critical for achieving full catalytic competence through intermolecular phosphorylation mechanisms.^[25]^[24] Unlike canonical cyclin-dependent kinases that require cyclin binding for activation, CDKL5 operates in a cyclin-independent manner, distinguishing it from traditional CMGC family members and allowing constitutive activity in neuronal contexts.^[26] Its kinase function is regulated primarily through autophosphorylation of the activation loop, which stabilizes the active conformation, as well as by intramolecular interactions between the N-terminal kinase domain and the C-terminal regulatory tail, which exerts a negative influence on basal activity—truncation of this tail enhances phosphorylation efficiency by approximately 1.5-fold in assays.^[25]^[24] The subcellular localization of CDKL5 influences its kinase roles, with the protein distributing to both cytoplasmic compartments, including dendritic spines for synaptic protein regulation, and the nucleus for involvement in transcription-coupled processes such as DNA damage response.^[25]^[27] Kinase activity assays reveal sensitivity to environmental factors, though specific pH and calcium dependencies remain undetailed in primary studies; however, CDKL5's synaptic functions are modulated by calcium influx in neurons.^[28] These parameters underscore CDKL5's efficient catalysis under physiological ATP levels, supporting its role in rapid neuronal signaling.

Biological Roles

Neuronal Development

CDKL5 plays a crucial role in promoting dendritic arborization and spine maturation in hippocampal and cortical neurons. Studies using primary neuronal cultures have demonstrated that CDKL5 regulates dendritic complexity through kinase-mediated phosphorylation events that influence cytoskeletal organization, leading to enhanced branching and maturation of dendritic spines essential for synaptic connectivity.^[29] Knockout models reveal significantly reduced spine density in these neurons, underscoring CDKL5's necessity for maintaining proper dendritic architecture during early brain development.^[29] CDKL5 also contributes to neuronal migration during embryogenesis and axon guidance by modulating cytoskeletal dynamics. In human iPSC-derived neurons, CDKL5 phosphorylates targets such as GTF2I, which regulates genes involved in axon guidance, and PPP1R35, which supports microtubule organization critical for migration and centrosome function.^[30] These phosphorylation events facilitate efficient cytoskeletal remodeling, enabling proper neuronal positioning and pathfinding in the developing brain.^[30] Furthermore, CDKL5 supports neuronal survival through anti-apoptotic signaling pathways, particularly via modulation of AKT/GSK-3β activity. In rodent models, loss of CDKL5 leads to increased apoptosis in newborn neurons, with elevated cleaved caspase-3 levels indicating heightened cell death rates, while wild-type CDKL5 expression maintains survival of postmitotic granule neurons.^[31] CDKL5 expression increases during critical windows of synaptogenesis in rodents, from late embryonic stages through postnatal day 21 (P21), with levels peaking around postnatal day 14 before stabilizing, aligning with periods of intense neuronal maturation and network formation.^[32] In vitro studies provide direct evidence of CDKL5's influence on neuronal morphology, showing that overexpression in primary cultures significantly enhances neuronal polarization by promoting the formation of multiple axons and branching, though individual axon length is reduced, essential for initial neuronal polarization.^[33]

Molecular Interactions

CDKL5, as a serine/threonine kinase, phosphorylates several key substrates that influence neuronal function. One prominent substrate is MeCP2; CDKL5 has been reported to bind and phosphorylate MeCP2, potentially modulating its transcriptional repressor activity and contributing to synaptic plasticity, though the exact sites and direct substrate status remain under investigation.^[34]^[20] This phosphorylation event has been demonstrated both in vitro, using recombinant proteins, and in vivo in neuronal models, highlighting CDKL5's role in regulating MeCP2-dependent gene expression during neural maturation.^[20] Other identified substrates include microtubule-associated proteins such as MAP1S, EB2 (MAPRE2), and ARHGEF2, which CDKL5 phosphorylates to stabilize cytoskeletal dynamics essential for neuronal morphology.^[35] In the nucleus, CDKL5 localizes to nuclear speckles and interacts with splicing factors, including the SR protein SC35 and other SR proteins, to regulate alternative splicing of pre-mRNA. These interactions indirectly control splicing factor dynamics, as CDKL5 overexpression disrupts speckle integrity while its depletion leads to enlarged, irregular speckles, thereby influencing RNA processing events critical for neuronal gene expression.^[36] Although direct phosphorylation of SC35 by CDKL5 has not been confirmed, the kinase activity of CDKL5 is required for maintaining normal speckle morphology and splicing efficiency, as shown in minigene assays reporting altered exon inclusion patterns upon CDKL5 modulation.^[36] Cytoplasmically, CDKL5 associates with the actin cytoskeleton and binds to the scaffold protein talin, facilitating modulation of the actin cytoskeleton and synaptic anchoring. This interaction with talin positions CDKL5 at the postsynaptic density through PDZ domain associations, supporting cytoskeletal remodeling in dendrites. Additionally, CDKL5's binding to PSD-95 promotes its synaptic localization, enhancing excitatory synapse stability indirectly via phosphorylation of upstream partners like NGL-1, which strengthens NGL-1–PSD-95 associations.^[37]^[38] CDKL5 participates in signaling pathways such as MAPK/ERK, where it contributes to dendritic spine plasticity by integrating kinase cascades that respond to synaptic activity. In CDKL5-deficient models, dysregulation of MAPK/ERK signaling correlates with impaired spine morphogenesis, underscoring CDKL5's role in activity-dependent neuronal adaptation. Furthermore, CDKL5 engages in regulatory networks with autism-related genes, including SHANK3, where mutations in either disrupt postsynaptic signaling, and CDKL5 expression is reduced in SHANK3 knockout models.^[39] Proteomic analyses using immunoprecipitation-mass spectrometry (IP-MS) have identified over 50 potential interactors of CDKL5 in neuronal cells, encompassing splicing factors, cytoskeletal elements, and synaptic proteins, with binding affinities for key partners like talin and PSD-95 in the micromolar range (Kd ≈ 1–10 μM). These data, derived from human iPSC-derived neurons, confirm CDKL5's broad regulatory scope across nuclear and cytoplasmic compartments.^[40]

CDKL5 Deficiency Disorder

Clinical Features

CDKL5 deficiency disorder (CDD) is a severe neurodevelopmental disorder primarily affecting females, characterized by early-onset epilepsy, profound intellectual disability, and significant developmental delays. The condition manifests in infancy with a spectrum of symptoms that profoundly impact quality of life, including refractory seizures, motor impairments, and sensory processing issues. While the core features are consistent across cases, variability exists influenced by genetic factors such as mutation type.^[2] The hallmark symptom is epilepsy, occurring in over 99% of individuals, with onset typically within the first two months of life and infantile spasms affecting approximately 90% of cases before three months. These seizures are often refractory to multiple antiepileptic drugs, evolving into various types including tonic-clonic and myoclonic seizures, and may temporarily improve in about 40% of cases around ages 1-2 years before recurring. Profound intellectual disability is universal, with no individuals achieving independent communication or cognitive milestones beyond basic recognition. Gross motor delays are prominent, featuring early hypotonia; only about 60% achieve supported sitting by age 2, and roughly 20% walk independently, often with assistive devices.^[2]^[41]^[2] Additional clinical features include hand stereotypies, such as repetitive mouthing or clapping, observed in the majority of affected individuals, alongside arm flapping and leg crossing behaviors. Sensory impairments are common, with cerebral visual impairment reported in 80% of cases, manifesting as poor eye contact and abnormal tracking, and auditory processing difficulties in severe cases leading to absent auditory tracking. Musculoskeletal issues like scoliosis affect around 20% of individuals, often requiring orthopedic intervention. Sleep disturbances occur in 87-90% of cases, characterized by frequent awakenings and irregular sleep-wake cycles persisting lifelong. Gastrointestinal comorbidities, including constipation (71%) and gastroesophageal reflux (64%), impact 70-87% of patients. The disorder shows female predominance with a 4:1 ratio, while affected males, comprising about 20% of cases, often exhibit more severe phenotypes and higher lethality, with many succumbing in the first or second decade of life due to complications.^[2]^[41]^[41] Disease progression typically involves an early regression phase between 6 and 18 months, where previously acquired skills such as rolling or reaching are lost amid escalating seizures and hypotonia. After age 5, development often plateaus, with some stabilization in seizure frequency but persistent severe impairments; however, progressive challenges like brain atrophy can emerge. Phenotypic variability correlates with mutation type: truncating variants distal to amino acid 781 may allow earlier motor milestones compared to proximal truncations, whereas certain missense mutations, like p.Arg178Trp, are associated with more severe epilepsy and developmental delay.^[41]^[2]^[41] Epidemiologically, CDD has an estimated incidence of 2.36 per 100,000 live births, or approximately 1 in 42,000. Life expectancy is reduced and variable, influenced by seizure control and comorbidities; while some individuals survive into their 40s or 50s with supportive care, severe cases, particularly in males, face higher mortality risks in early adulthood.^[2]^[42]^[43]

Diagnosis

The diagnosis of CDKL5 deficiency disorder (CDD) is established by identifying a pathogenic variant in the CDKL5 gene in individuals with suggestive clinical features, such as early-onset refractory epilepsy and severe developmental delay.^[2] Genetic testing typically begins with targeted sequencing of the CDKL5 gene to detect point mutations, including missense, nonsense, and splice site variants, which comprise about 84% of identified cases; this is often complemented by multiplex ligation-dependent probe amplification (MLPA) or array-based methods to identify deletions or duplications accounting for the remaining 16%.^[2]^[44] CDKL5 is routinely included in multigene panels for developmental and epileptic encephalopathies (DEEs), where pathogenic variants yield a diagnosis in approximately 2%-5% of cases with infantile-onset epilepsy.^[2] Comprehensive genomic approaches, such as exome sequencing, may be used if initial testing is negative, particularly to uncover mosaicism or non-coding variants.^[2] Clinical evaluation plays a key role in prompting genetic testing, with early seizures (often within the first 3 months of life) and profound psychomotor delays serving as primary indicators; electroencephalogram (EEG) patterns frequently include hypsarrhythmia, epileptic spasms, or multifocal discharges, though early EEGs may appear normal.^[45] International consensus recommends baseline EEG assessment in all suspected cases to guide testing urgency.^[45] In families with a known CDKL5 variant, prenatal screening via amniocentesis or chorionic villus sampling enables early detection, while postnatal testing follows standard newborn or infant protocols for high-risk cases.^[2] Exploratory biomarkers, such as distinct cerebrospinal fluid (CSF) proteome alterations (e.g., elevated levels of certain synaptic and metabolic proteins), show promise for supporting diagnosis but remain investigational and non-routine.01238-X) Differential diagnosis requires distinguishing CDD from phenotypically overlapping conditions, such as Rett syndrome (via MECP2 testing) or other DEEs involving genes like FOXG1 or SCN1A; guidelines emphasize sequential or panel-based genetic testing to resolve ambiguities.^[2]^[45]

Pathophysiology

CDKL5 mutations predominantly result in loss-of-function, impairing the kinase's ability to phosphorylate key substrates and leading to their hypophosphorylation. This disruption affects synaptic plasticity by reducing the number of excitatory synapses, decreasing levels of postsynaptic density protein 95 (PSD-95) and synapsin I, and causing dendritic spine hypotrophy. Consequently, the localization and trafficking of AMPA (GluA2) and NMDA (GluN2B) receptors are compromised, contributing to impaired neuronal connectivity and function.^[2]^[20] In the nucleus, CDKL5 deficiency causes dysfunction by altering the splicing of neuronal transcripts through its association with nuclear speckles and interactions with splicing factors. Models of the disorder demonstrate widespread effects on pre-mRNA processing, impacting the expression and maturation of numerous neuronal genes essential for development. Cytoplasmically, the loss of CDKL5 dysregulates RhoA signaling via impaired phosphorylation of guanine nucleotide exchange factor ARHGEF2 at serine 122, leading to defects in neuronal migration and dendritic spine morphology. These combined nuclear and cytoplasmic disruptions underlie the core pathological changes in neuronal maturation and maintenance.^[20]^[46] Epilepsy in CDKL5 deficiency arises from neuronal hyperexcitability, primarily due to deficits in GABAergic interneurons that fail to provide adequate inhibitory control. Additionally, microglial activation promotes neuroinflammation, exacerbating circuit dysfunction and seizure susceptibility. Sex-specific effects further modulate disease severity: in females, skewed X-chromosome inactivation leads to variable CDKL5 expression levels, while mosaic males experience near-complete loss in affected cells. Quantitative models indicate that a 50-70% reduction in CDKL5 activity represents a critical threshold for manifesting disorder-related deficits.^[47]

Research and Therapies

Animal Models

Animal models have been essential for elucidating the roles of CDKL5 in neurodevelopment and the mechanisms underlying CDKL5 deficiency disorder (CDD). Primary preclinical systems include mouse knockouts and other vertebrate and cellular models that recapitulate key pathological features such as seizures, synaptic alterations, and behavioral deficits. Full Cdkl5 knockout mice, both hemizygous males and heterozygous females, develop spontaneous seizures starting around postnatal day 10 (P10), alongside reduced dendritic spine density and stability in cortical regions like the somatosensory and visual cortices.^[48]^[49] Conditional knockouts, such as those targeting GABAergic or glutamatergic neurons, further demonstrate cell-type-specific effects, including autistic-like behaviors and impaired excitatory-inhibitory balance.^[50] These models exhibit a high degree of phenotypic homology to human CDD, recapitulating approximately 80% of epilepsy features, though with limitations like incomplete seizure penetrance in some lines.^[11] Behavioral assays, including the elevated plus maze, reveal enhanced anxiety-like responses, with knockout mice spending less time in open arms compared to wild-type controls.^[51] Knockin mouse models mimicking patient mutations provide additional insights into variant-specific effects. For instance, the Cdkl5^{E364X} knockin line shows hyperactivity, motor coordination deficits, and impaired memory and cognition from early development.^[52] A 2025 CRISPR-generated knockin model with a C-terminal truncating mutation (Cdkl5^{492stop}) demonstrates protein instability via nonsense-mediated mRNA decay, leading to severe neurological phenotypes in males and offering a platform to study mosaic expression patterns relevant to X-linked inheritance.^[53] Beyond mice, zebrafish models using morpholino-mediated Cdkl5 knockdown or stable mutants exhibit neuronal migration and branching defects, including reduced motor neuron axonal density and impaired neuromuscular connectivity, alongside microcephaly and motor dysfunction.^[54] These phenotypes emerge early in development and mirror human motor impairments. Induced pluripotent stem cell (iPSC)-derived neurons from CDD patients reveal synaptic deficits, such as reduced excitatory synapse density and altered network excitability, providing a human-relevant cellular system for mechanistic studies.^[55] Overall, these models validate CDKL5's critical functions in neuronal maturation while highlighting challenges like variable epilepsy expressivity for translational research.

Emerging Treatments

Gene therapy represents a promising approach for treating CDKL5 deficiency disorder (CDD) by delivering a functional copy of the CDKL5 gene to the central nervous system. UX055, an investigational AAV9-based vector developed by Ultragenyx Pharmaceutical, is in preclinical development and aims to restore CDKL5 expression in neurons. As of November 2025, the program has faced delays in investigational new drug (IND) filing but continues to advance toward clinical trials, with preclinical studies in Cdkl5 knockout mouse models demonstrating dose-dependent restoration of neuronal architecture, synapse function, and behavioral phenotypes. In these models, intracerebroventricular administration at high doses achieved CDKL5 protein levels of approximately 40-60% of wild-type in key brain regions, leading to significant improvements in motor coordination and seizure susceptibility. Challenges include achieving broad brain distribution across the blood-brain barrier and mitigating immune responses to the AAV vector. Small molecule therapies are being explored to activate residual CDKL5 kinase activity or promote read-through of nonsense mutations, which account for about 15% of CDKL5 variants. Preclinical studies have shown that aminoglycoside antibiotics and ataluren promote efficient read-through of premature termination codons in CDKL5, partially restoring kinase function, though the resulting protein remains hypomorphic with limited efficacy in vivo. Angel Neurotherapeutics is advancing PME, a small molecule kinase modulator, in preclinical stages, with data from 2025 presentations indicating potential to enhance CDKL5 signaling pathways and ameliorate neurodevelopmental deficits in mouse models without the delivery challenges of biologics. Antisense oligonucleotides (ASOs) and epigenetic strategies target splicing defects and X-chromosome inactivation, which affect a subset of CDD patients, particularly females. ASO-mediated splicing correction, including U1 snRNA-based approaches, has been shown in cellular models to fully restore wild-type CDKL5 isoform production and kinase activity for specific intronic mutations. n-Lorem's personalized ASO program includes candidates for CDKL5 variants amenable to splicing modulation, with preclinical proof-of-concept demonstrating increased functional protein levels. Epigenetic reactivation of the silenced wild-type CDKL5 allele on the inactive X chromosome is under investigation using CRISPR-based editors, showing reversal of mosaic expression patterns and improved neuronal maturation in patient-derived models. Investigational antiseizure therapies, often evaluated as adjuncts, include fenfluramine, supported by phase 3 data from the GEMZ study (NCT05064878, completed June 2025), which met its primary endpoint of significant reduction in convulsive seizures as add-on therapy.^[56] Ongoing regulatory discussions follow these results. Key hurdles across these modalities include optimizing central nervous system penetration and addressing variability in mutation-specific responses.

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Palmitoylation-dependent CDKL5–PSD-95 interaction regulates ...
May 13, 2013 · We show that CDKL5 binds to the scaffolding protein postsynaptic density (PSD)-95, and that this binding promotes the targeting of CDKL5 to excitatory synapses.Missing: EBNA1BP2 | Show results with:EBNA1BP2
[37]
Cyclin-dependent kinase-like 5 (CDKL5) binds to talin and ... - bioRxiv
Aug 28, 2025 · Cyclin-dependent kinase-like 5 (CDKL5) binds to talin and is anchored at the postsynaptic density via direct interaction with PDZ domains.
[38]
Loss of CDKL5 disrupts kinome profile and event-related potentials ...
We found that mice lacking CDKL5 show autistic-like behavioral abnormalities, deficits in neural circuit communication, and alterations in multiple signal ...
[39]
Novel CDKL5 targets identified in human iPSC-derived neurons - PMC
CDKL5 Deficiency Disorder (CDD) is a debilitating epileptic encephalopathy disorder affecting young children with no effective treatments.
[40]
CDKL5 deficiency disorder: clinical features, diagnosis, and ...
It is characterised by early-onset (generally within the first 2 months of life) seizures that are usually refractory to polypharmacy.
[41]
CDKL5 Deficiency Disorder - Symptoms, Causes, Treatment | NORD
Apr 25, 2024 · ... sleep disturbances. Although rare, the occurrence may be between ~1:40,000 and 1:60,000 livebirths, but an Australian population-based study ...
[42]
CDKL5 Deficiency Disorder (CDD)—Rare Presentation in Male - MDPI
Nov 24, 2022 · CDKL5 deficiency disorder (CDD) is a developmental encephalopathy caused by pathogenic variants in the X-linked cyclin-dependent kinase 5 (CDKL5) gene.Missing: hotspots | Show results with:hotspots
[43]
Optimizing the molecular diagnosis of CDKL5 gene-related epileptic ...
Sep 29, 2014 · Diagnosis is optimized by Sanger sequencing combined with array-based methods or MLPA; alternatively, NGS targeted resequencing designed to ...Missing: testing | Show results with:testing
[44]
International Consensus Recommendations for the Assessment and ...
Jun 20, 2022 · CDKL5 Deficiency Disorder (CDD) is a rare, X-linked dominant ... Those with a late truncating variant displayed better levels of ability than ...<|control11|><|separator|>
[45]
https://pmc.ncbi.nlm.nih.gov/articles/PMC9251467/
[46]
Deficiency of cyclin-dependent kinase like 5 causes spontaneous ...
Mar 9, 2020 · We present the first systematic study of spontaneous seizures in mouse models of CDD. We demonstrated epileptiform discharges in pups lacking CDKL5.
[47]
Temporal manipulation of Cdkl5 reveals essential ... - NIH
Oct 15, 2021 · We temporally manipulated endogenous Cdkl5 expression in male mice and found that postdevelopmental loss of CDKL5 disrupts numerous behavioral domains.Missing: P21 | Show results with:P21
[48]
Altered NMDAR signaling underlies autistic-like features in mouse ...
Jun 14, 2019 · Here, we find that selective loss of CDKL5 in GABAergic neurons leads to autistic-like phenotypes in mice accompanied by excessive glutamatergic ...
[49]
Comprehensive behavioral analysis of the Cdkl5 knockout mice ...
These results indicate that CDKL5 plays significant roles in regulating emotional behaviors especially on anxiety- and fear-related responses.
[50]
A new knockin mouse carrying the E364X patient mutation for ...
Nov 15, 2024 · The novel Cdkl5 E364X mouse showed altered neurological and motor neuron maturation, hyperactivity, defective coordination and impaired memory and cognition.
[51]
A Novel Mouse Model Unveils Protein Deficiency in Truncated ...
Mar 5, 2025 · After creating cell lines with various Cdkl5 truncating mutations, we found that these mutations are regulated by the nonsense-mediated RNA ...
[52]
Novel preclinical model for CDKL5 deficiency disorder - PMC
We show that cdkl5−/− zebrafish display reduced body and head size, defects in motor neuron branching and impaired motor function. Using live confocal imaging, ...Missing: migration | Show results with:migration
[53]
Altered network and rescue of human neurons derived from ... - Nature
Apr 22, 2021 · Mutations in this gene cause CDKL5 deficiency disorder (CDD), characterized by neurodevelopmental delay, motor dysfunction, autistic features, ...