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

Measuring the Burden of Epilepsy Hospitalizations in CDKL5 Deficiency Disorder

BACKGROUND

Information on the hospital service use among individuals with CDKL5 Deficiency Disorder, an ultrarare developmental epileptic encephalopathy, is limited, evidence of which could assist with service planning. Therefore, using baseline and longitudinal data on 379 genetically verified individuals in the International CDKL5 Disorder Database, we aimed to investigate rates of seizure-related and other hospitalizations and associated length of stay in this cohort.

METHODS

Outcome variables were lifetime count of family-reported hospitalizations and average length of stay both for seizure- (management and/or investigative) and non-seizure-related causes. These variables were examined according to gender, age group, genetic variant group, and lifetime number of antiseizure medications. Using negative binomial regression associations were expressed as incidence rate ratios and geometric mean ratios for hospitalization rates and length of stay, respectively.

RESULTS

There were 2880 hospitalizations over 2728.4 person-years with two thirds seizure related. Infants were much more likely to be hospitalized than older individuals, with decreasing effect sizes with increasing age. Males had slightly higher rates of hospitalizations for seizure-related management and for non-seizure-related admissions. Lifetime use of six or more antiseizure medications was associated with a higher hospitalization rate for seizure management than use of three or fewer medications. The median length of stay was five days for seizure and nonseizure reasons.

CONCLUSION

There is an urgent need for much better seizure management in CDKL5 deficiency disorder given the hospitalization burden especially in the preschool age group and the multiplicity of antiseizure medications being used.

The natural history of CDKL5 deficiency disorder into adulthood

Knowledge of the natural history of CDKL5 deficiency disorder (CDD) is limited to the results of cross-sectional analysis of largely pediatric cohorts. Assessment of outcomes in adulthood is critical for clinical decision-making and future precision medicine approaches but is challenging because of the diagnostic gap and duration of follow-up that would be required for prospective studies. We aimed to delineate the natural history retrospectively from adulthood. We analyzed clinical data about an international cohort of 67 adults with CDD. We analyzed demographic, phenotypic, CDKL5 Developmental Score (CDS), and treatment data, and tested associations with genetic factors, sex, and a positive or negative history of neonatal seizures, as an early predictor of prognosis. All but one of 67 adults (55 females, median age of 24 years at last follow-up) had epilepsy, typically beginning with epileptic spasms or tonic seizures before 4 months of age. Focal-onset and non-motor seizures emerged later. Fewer than a third had been documented as having bilateral tonic-clonic seizures or status epilepticus. Seizures often improved with age, but 73% had never experienced more than 6 months of seizure-freedom. Clobazam, sodium valproate, and lamotrigine were the most frequently prescribed antiseizure medications, but no specific treatment demonstrated superiority. Common comorbidities included movement disorders, visual impairment, sleep disorders, constipation, and scoliosis. All participants had intellectual disability, 75% had not acquired speech and 45% had regressed developmentally. 16% never achieved any CDS skill, but most attained at least three, and 28% attained six or all seven. By adulthood, half of those who had achieved any CDS skill retained all their CDS skills. The skills most frequently lost were independent walking and standing. Those with a history of neonatal seizures tended to attain fewer CDS skills and were more likely to have abnormal muscle tone in adulthood, atrioventricular conduction delay, and potential complications of their illness and treatment. Individuals carrying missense variants attained more CDS skills than those with other variants and were more likely to lose skills in adulthood and develop anxiety, possibly reflecting the limited neurodevelopment of those with non-missense variants, who manifested a more multisystemic disorder. In summary, retrospective data from adulthood elucidates the evolution of symptoms, variation in developmental outcomes, and the treatment landscape in CDKL5 deficiency disorder. Presence a non-missense variants or a history of neonatal seizures indicates a more complex disorder and lower developmental trajectory. Our findings will inform management decisions, prognostication, and the design of clinical trials in CDKL5 Deficiency Disorder.

Deletions in the CDKL5 5' untranslated region lead to CDKL5 deficiency disorder

Pathogenic variants in the cyclin-dependent kinase-like 5 (CDKL5) gene are associated with CDKL5 deficiency disorder (CDD), a severe X-linked developmental and epileptic encephalopathy. Deletions affecting the 5' untranslated region (UTR) of CDKL5, which involve the noncoding exon 1 and/or alternatively spliced first exons (exons 1a-e), are uncommonly reported. We describe genetic and phenotypic characteristics for 15 individuals with CDKL5 partial gene deletions affecting the 5' UTR. All individuals presented characteristic features of CDD, including medically refractory infantile-onset epilepsy, global developmental delay, and visual impairment. We performed RNA sequencing on fibroblast samples from three individuals with small deletions involving exons 1 and/or 1a/1b only. Results demonstrated reduced CDKL5 mRNA expression with no evidence of expression from alternatively spliced first exons. Our study broadens the genotypic spectrum for CDD by adding to existing evidence that deletions affecting the 5' UTR of the CDKL5 gene are associated with the disorder. We propose that smaller 5' UTR deletions may require additional molecular testing approaches such as RNA sequencing to determine pathogenicity.

A new knockin mouse carrying the E364X patient mutation for CDKL5 deficiency disorder: neurological, behavioral and molecular profiling

CDKL5 deficiency disorder (CDD) is a rare neurodevelopmental syndrome caused by mutations in the X-linked CDKL5 gene. Hundreds of pathogenic variants have been described, associated with a significant phenotypic heterogeneity observed among patients. To date, different knockout mouse models have been generated. Here we present a new knockin CDKL5 mouse model carrying a humanized, well-characterized nonsense variant (c.1090G > T; p.E364X) described in the C-terminal domain of the CDKL5 protein in a female patient with a milder phenotype. Both male and female Cdkl5 E364X mice were analyzed. The novel Cdkl5 E364X mouse showed altered neurological and motor neuron maturation, hyperactivity, defective coordination and impaired memory and cognition. Gene expression analysis highlighted an unexpected reduction of Cdkl5 expression in Cdkl5 E364X mice brain tissues, with a significant increase in overall neuron-specific gene expression and an area-dependent alteration of astrocyte- and oligodendrocyte-specific transcripts. Moreover, our results showed that the loss of CDKL5 protein had the most significant impact on the cerebellum and hippocampus, compared to other analyzed tissues. A targeted analysis to study synaptic plasticity in cerebellum and hippocampus showed reduced Gabra1 and Gabra5 expression levels in females, whereas Gabra1 expression was increased in males, suggesting an opposite, sex-dependent regulation of the GABA receptor expression already described in humans. In conclusion, the novel Cdkl5E364X mouse model is characterized by robust neurological and neurobehavioral alterations, associated with a molecular profile related to synaptic function indicative of a cerebellar GABAergic hypofunction, pointing to Gabra1 and Gabra5 as novel druggable target candidates for CDD.

Excitatory Cortical Neurons from CDKL5 Deficiency Disorder Patient-Derived Organoids Show Early Hyperexcitability Not Identified in Neurogenin2 Induced Neurons

CDKL5 deficiency disorder (CDD) is a rare developmental and epileptic encephalopathy resulting from variants in cyclin-dependent kinase-like 5 (CDKL5) that lead to impaired kinase activity or loss of function. CDD is one of the most common genetic etiologies identified in epilepsy cohorts. To study how CDKL5 variants impact human neuronal activity, gene expression and morphology, CDD patient-derived induced pluripotent stem cells and their isogenic controls were differentiated into excitatory neurons using either an NGN2 induction protocol or a guided cortical organoid differentiation. Patient-derived neurons from both differentiation paradigms had decreased phosphorylated EB2, a known molecular target of CDKL5. Induced neurons showed no detectable differences between cases and isogenic controls in network activity using a multielectrode array, or in MAP2+ neurite length, and only two genes were differentially expressed. However, patient-derived neurons from the organoid differentiation showed increased synchrony and weighted mean firing rate on the multielectrode array within the first month of network maturation. CDD patient-derived cortical neurons had lower expression of CDKL5 and HS3ST1, which may change the extracellular matrix around the synapse and contribute to hyperexcitability. Similar to the induced neurons, there were no differences in neurite length across or within patient-control cell lines. Induced neurons have poor cortical specification while the organoid derived neurons expressed cortical markers, suggesting that the changes in neuronal excitability and gene expression are specific to cortical excitatory neurons. Examining molecular mechanisms of early hyperexcitability in cortical neurons is a promising avenue for identification of CDD therapeutics.

Psychometric evaluation of clinician- and caregiver-reported clinical severity assessments for individuals with CDKL5 deficiency disorder

OBJECTIVE

The CDKL5 Clinical Severity Assessment (CCSA) is a comprehensive, content-validated measurement tool capturing the diverse challenges of cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD), a genetically caused developmental epileptic encephalopathy (DEE). The CCSA is divided into clinician-reported (CCSA-Clinician) and caregiver-reported (CCSA-Caregiver) assessments. The aim of this study was to evaluate the factor structure of these measures through confirmatory factor analysis (CFA) and evaluate their validity and reliability.

METHODS

Participants were recruited from the International CDKL5 Clinical Research Network to take part in an in-clinic CCSA-Clinician evaluation (n = 148) and/or complete the CCSA-Caregiver questionnaire (n = 198). CFA was used to determine domains, and factor loadings and validity were assessed. For the CCSA-Clinician, inter-rater reliability was assessed by nine CDD experienced clinicians via 14 pre-recorded evaluations. Eight clinicians re-viewed and re-scored the videos after 4 weeks to evaluate intra-rater reliability. The CCSA-Caregiver was completed on a second occasion by 34 caregivers after 2-4 weeks to assess test-retest reliability.

RESULTS

CFA resulted in three domains for the CCSA-Clinician (motor and movement, communication, vision) and four domains for the CCSA-Caregiver (seizures, behavior, alertness, feeding), with good item loadings across both measures. Structural statistics, internal consistency, discriminant validity, and reliability were satisfactory for both measures, and scores were consistent between known groups.

SIGNIFICANCE

This study provides strong evidence that the CCSA measures are suitable to assess the clinical severity of individuals with CDD, supporting their use in clinical trials. Further evaluation of responsiveness to change in a longitudinal assessment is planned. Use may also be appropriate in similar DEEs but would require validation in those populations.

Caregiver Perspective of Benefits and Side Effects of Anti-Seizure Medications in CDKL5 Deficiency Disorder from an International Database

BACKGROUND AND OBJECTIVE

CDKL5 deficiency disorder presents as a challenging condition with early-onset refractory seizures, severe developmental delays, and a range of other neurological symptoms. Our study aimed to explore the benefits and side effects of anti-seizure medications (ASMs) in managing seizures among individuals with CDKL5 deficiency disorder, drawing on data from the International CDKL5 Disorder Database.

METHODS

Data for this retrospective cohort study were obtained from the International CDKL5 Disorder Database, which contains responses from a baseline questionnaire administered between 2012 and 2022 and a follow-up questionnaire administered between 2018 and 2019. Families of eligible individuals were asked to provide information on ASMs that were previously and currently taken, the dose prescribed, the age at starting the medications, and the age at discontinuation for past medications. The outcome variables of interest were perceived seizure-related benefits for the current and past use of ASMs and caregiver-reported side effects. Rescue medications and infrequently used ASMs were excluded from the analysis. Descriptive statistics were used to summarise the characteristics of the study population.

RESULTS

The study included 399 children and adults with CDKL5 deficiency disorder, descriptively analysing the perceived benefits and side effects of 23 unique ASMs based on caregiver reports. The study identified levetiracetam, topiramate, sodium valproate, vigabatrin, phenobarbital and clobazam as the most used ASMs. Notably, cannabidiol showed highly beneficial outcomes with few side effects, whereas levetiracetam and phenobarbital exhibited less favourable benefit-to-side-effect ratios. Dual therapy involving sodium valproate and levetiracetam was only used a small number (n = 5) of times but appeared effective in reducing seizure activity with relatively few side effects. Compared with monotherapy, polytherapy had a relatively higher likelihood of reported side effects than benefits.

CONCLUSIONS

The study, leveraging a large sample size that exceeds that of previous research, emphasises the complex nature of seizure management in CDKL5 deficiency disorder. Our findings underscore the necessity of ongoing research to optimise treatment strategies, considering both the efficacy of seizure control and the potential for adverse effects. The study also points to the need for future investigations into the therapeutic potential of emerging treatments such as ganaxolone and the unresolved efficacy of cannabis products in seizure management.

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.

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.

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.

CDKL5 Deficiency Disorder Without Epilepsy

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) has epilepsy as a cardinal feature. Here we report two new female patients and review six previously published patients, one male and five females, with features of CDD but who never developed epilepsy. In contrast with the classical and severe CDD phenotype, they presented with milder gross motor delays, autism spectrum disorder, and no visual cortical impairment. Prolonged video electroencephalography was normal in adult cases but showed interictal frontal-temporal bilateral spikes and sharp waves in sleep in the three-year-old girl. Causative CDKL5 variants included two likely gene damaging (nonsense and frameshift) and six missense variants, being de novo or maternally inherited from asymptomatic females with skewed X-chromosome inactivation (two missense variants). Our data indicate that a milder form of CDD without epilepsy can occur in some cases without clear correlation with specific variants in the CDKL5 gene.

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 deficiency causes epileptic seizures independent of cellular mosaicism

OBJECTIVE

In a study using a mouse model of CDKL5 deficiency disorder (CDD), seizures are specific to female mice heterozygous for Cdkl5 mutations and not observed in hemizygous knockout males or homozygous knockout females. The aim of this study was to examine whether the clinical phenotype of patients with CDD can be impacted by the type of genetic variant.

METHODS

Eleven CDD patients (six females and five males) were included in this study. The molecular diagnosis of hemizygous male patients was performed using digital PCR and their clinical phenotypes were compared with those of patients with mosaic or heterozygous CDKL5 variants. The severity of clinical phenotypes was graded by using CDKL5 Developmental Score and the adapted version of the CDKL5 Clinical Severity Assessment. The effect of cellular mosaicism on the severity of CDD was studied by comparing the clinical characteristics and comorbidities between individuals with hemizygous and mosaic or heterozygous CDKL5 variants.

RESULTS

One of the five male patients was mosaic for the CDKL5 variant. All patients developed seizures irrespective of their genetic status of the pathogenic variant. However, cellular mosaicism of CDKL5 deficiency was associated with lesser severity of other comorbidities such as feeding, respiratory, and visual functional impairments.

SIGNIFICANCE

This study provided evidence that cellular mosaicism of CDKL5 deficiency was not necessarily required for developing epilepsy. CDD patients not only exhibited clinical features of epilepsy but also exhibited the developmental consequences arising directly from the effect of the CDKL5 pathogenic variant.

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.

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.

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 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.

Genetic analysis using targeted exome sequencing of 53 Vietnamese children with developmental and epileptic encephalopathies

Developmental and epileptic encephalopathies (DEE) refers to a group of rare and severe neurodevelopmental disorders where genetic etiologies can play a major role. This study aimed to elucidate the genetic etiologies of a cohort of 53 Vietnamese patients with DEE. All patients were classified into known electroclinical syndromes where possible. Exome sequencing (ES) followed by a targeted analysis on 294 DEE-related genes was then performed. Patients with identified causative variants were followed for 6 months to determine the impact of genetic testing on their treatment. The diagnostic yield was 38.0% (20/53), which was significantly higher in the earlier onset group (<12 months) than in the later onset group (≥12 months). The 19 identified variants belonged to 11 genes with various cellular functions. Genes encoding ion channels especially sodium voltage-gated channel were the most frequently involved. Most variants were missense variants and located in key protein functional domains. Four variants were novel and four had been reported previously but in different phenotypes. Within 6 months of further follow-up, treatment changes were applied for six patients based on the identified disease-causing variants, with five patients showing a positive impact. This is the first study in Vietnam to analyze the genetics of DEE. This study confirms the strong involvement of genetic etiologies in DEE, especially early onset DEE. The study also contributes to clarify the genotype-phenotype correlations of DEE and highlights the efficacy of targeted ES in the diagnosis and treatment of DEE.

Analysis of X-inactivation status in a Rett syndrome natural history study cohort

BACKGROUND

Rett syndrome (RTT) is a rare neurodevelopmental disorder associated with pathogenic MECP2 variants. Because the MECP2 gene is subject to X-chromosome inactivation (XCI), factors including MECP2 genotypic variation, tissue differences in XCI, and skewing of XCI all likely contribute to the clinical severity of individuals with RTT.

METHODS

We analyzed the XCI patterns from blood samples of 320 individuals and their mothers. It includes individuals with RTT (n = 287) and other syndromes sharing overlapping phenotypes with RTT (such as CDKL5 Deficiency Disorder [CDD, n = 16]). XCI status in each proband/mother duo and the parental origin of the preferentially inactivated X chromosome were analyzed.

RESULTS

The average XCI ratio in probands was slightly increased compared to their unaffected mothers (73% vs. 69%, p = .0006). Among the duos with informative XCI data, the majority of individuals with classic RTT had their paternal allele preferentially inactivated (n = 180/220, 82%). In sharp contrast, individuals with CDD had their maternal allele preferentially inactivated (n = 10/12, 83%). Our data indicate a weak positive correlation between XCI skewing ratio and clinical severity scale (CSS) scores in classic RTT patients with maternal allele preferentially inactivated XCI (r_s  = 0.35, n = 40), but not in those with paternal allele preferentially inactivated XCI (r_s  = -0.06, n = 180). The most frequent MECP2 pathogenic variants were enriched in individuals with highly/moderately skewed XCI patterns, suggesting an association with higher levels of XCI skewing.

CONCLUSION

These results extend our understanding of the pathogenesis of RTT and other syndromes with overlapping clinical features by providing insight into the both XCI and the preferential XCI of parental alleles.

Influences on the trajectory and subsequent outcomes in CDKL5 deficiency disorder

OBJECTIVE

The study investigated the effect of seizure and medication burden at initial contact with the International CDKL5 Disorder Database on subsequent development and clinical severity and compared quality of life among those whose development progressed, remained stable, or regressed between baseline and follow-up.

METHODS

The effects of seizure and medication burden at baseline (high or low) on the CDKL5 Disorder Severity Scores and CDKL5 Developmental Score (CDS) at follow-up were assessed using linear and negative binomial regressions, respectively, with adjustment for age at baseline, gender, and follow-up duration with and without genotype. Seizure and medication burden were defined by average daily seizure count (high, ≥5/day; low, <5/day) and number of antiseizure medications (high, ≥3/day; low, <3/day), respectively. The effects of change in CDS over time (improved, stable, or deteriorated) on Quality of Life Inventory-Disability (QI-Disability) total and domain scores at follow-up were assessed in those aged at least 3 years at follow-up using linear regression models with adjustment for baseline CDS, gender, and follow-up duration.

RESULTS

The expected follow-up CDS was lower for individuals with high compared to low seizure burden at baseline (β = -.49, 95% confidence interval [CI] = -.84 to -.13). The average total QI-Disability score was 5.6 (95% CI = -.2 to 11.5) points higher among those with improved compared with stable or deteriorating CDS and 8.5 (95% CI = 3.1-13.8) points lower for those with deteriorating compared to stable or improved CDS.

SIGNIFICANCE

Our finding that later development showed slight improvement in those with better earlier seizure control even after adjustment for genotype suggests that the trajectory for an individual child is not necessarily predetermined and could possibly be influenced by optimal seizure management. This has implications for children's quality of life.

CDKL5 deficiency disorder in males: Five new variants and review of the literature

The X-linked Cyclin-Dependent Kinase-Like 5 (CDKL5) gene encodes a serine-threonine kinase highly expressed in the developing brain. Loss of function of CDKL5 is pointed out to underlie the CDKL5 Deficiency Disorder (CDD), an X-linked dominant disease characterized by early-onset epileptic encephalopathy and developmental delay, usually affecting females more than males. To the best to our knowledge, only 45 males with CDD have been reported so far. Type and position of CDKL5 variants with different impact on the protein are reported to influence the clinical presentation. X-chromosome inactivation occurring in females and post-zygotic mosaicism in males are also believed to contribute to this variability. Based on these issues, genotype-phenotype correlations are still challenging. Here, we describe clinical features of five additional affected males with unreported CDKL5 variants, expanding the molecular spectrum of the disorder. We also reviewed the clinical profile of the previously reported 45 males with molecularly confirmed CDD. Severe developmental delay, cortical visual impairment, and early-onset refractory epilepsy characterize the CDD picture in males. By assessing the molecular spectrum, we confirm that germ-line truncating CDKL5 variants, equally distributed across the coding sequence, are the most recurrent mutations in CDD, and cause the worsen phenotype. While recurrence and relevance of missense substitutions within C-terminal remain still debated, disease-causing missense changes affecting the N-terminal catalytic domain correlate to a severe clinical phenotype. Finally, our data provide evidence that post-zygotic CDKL5 mosaicism may result in milder phenotypes and, at least in a subset of subjects, in variable response to antiepileptic treatments.

Clinical Trial Design for Disease-Modifying Therapies for Genetic Epilepsies

Although trials with anti-seizure medications (ASMs) have not shown clear anti-epileptogenic or disease-modifying activity in humans to date, rapid advancements in genomic technology and emerging gene-mediated and gene replacement options offer hope for the successful development of disease-modifying therapies (DMTs) for genetic epilepsies. In fact, more than 26 potential DMTs are in various stages of preclinical and/or clinical development for genetic syndromes associated with epilepsy. The scope of disease-modification includes but is not limited to effects on the underlying pathophysiology, the condition's natural history, epilepsy severity, developmental achievement, function, behavior, sleep, and quality of life. While conventional regulatory clinical trials for epilepsy therapeutics have historically focused on seizure reduction, similarly designed trials may prove ill-equipped to identify these broader disease-modifying benefits. As we look forward to this pipeline of DMTs, focused consideration should be given to the challenges they pose to conventional clinical trial designs for epilepsy therapeutics. Just as DMTs promise to fundamentally alter how we approach the care of patients with genetic epilepsy syndromes, DMTs likewise challenge how we traditionally construct and measure the success of clinical trials. In the following, we briefly review the historical and preclinical frameworks for DMT development for genetic epilepsies and explore the many novel challenges posed for such trials, including the choice of suitable outcome measures, trial structure, timing and duration of treatment, feasible follow-up period, varying safety profile, and ethical concerns.

Patient-Derived Induced Pluripotent Stem Cells (iPSCs) and Cerebral Organoids for Drug Screening and Development in Autism Spectrum Disorder: Opportunities and Challenges

Autism spectrum disorder (ASD) represents a group of neurodevelopmental diseases characterized by persistent deficits in social communication, interaction, and repetitive patterns of behaviors, interests, and activities. The etiopathogenesis is multifactorial with complex interactions between genetic and environmental factors. The clinical heterogeneity and complex etiology of this pediatric disorder have limited the development of pharmacological therapies. The major limit to ASD research remains a lack of relevant human disease models which can faithfully recapitulate key features of the human pathology and represent its genetic heterogeneity. Recent advances in induced pluripotent stem cells (iPSCs), reprogrammed from somatic cells of patients into all types of patient-specific neural cells, have provided a promising cellular tool for disease modeling and development of novel drug treatments. The iPSCs technology allowed not only a better investigation of the disease etiopathogenesis but also opened up the potential for personalized therapies and offered new opportunities for drug discovery, pharmacological screening, and toxicity assessment. Moreover, iPSCs can be differentiated and organized into three-dimensional (3D) organoids, providing a model which mimics the complexity of the brain’s architecture and more accurately recapitulates tissue- and organ-level disease pathophysiology. The aims of this review were to describe the current state of the art of the use of human patient-derived iPSCs and brain organoids in modeling ASD and developing novel therapeutic strategies and to discuss the opportunities and major challenges in this rapidly moving field.