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

Rett syndrome: a neurological disorder with metabolic components

Rett syndrome (RTT) is a neurological disorder caused by mutations in the X-linked gene methyl-CpG-binding protein 2 (MECP2), a ubiquitously expressed transcriptional regulator. Despite remarkable scientific progress since its discovery, the mechanism by which MECP2 mutations cause RTT symptoms is largely unknown. Consequently, treatment options for patients are currently limited and centred on symptom relief. Thought to be an entirely neurological disorder, RTT research has focused on the role of MECP2 in the central nervous system. However, the variety of phenotypes identified in Mecp2 mutant mouse models and RTT patients implicate important roles for MeCP2 in peripheral systems. Here, we review the history of RTT, highlighting breakthroughs in the field that have led us to present day. We explore the current evidence supporting metabolic dysfunction as a component of RTT, presenting recent studies that have revealed perturbed lipid metabolism in the brain and peripheral tissues of mouse models and patients. Such findings may have an impact on the quality of life of RTT patients as both dietary and drug intervention can alter lipid metabolism. Ultimately, we conclude that a thorough knowledge of MeCP2's varied functional targets in the brain and body will be required to treat this complex syndrome.

The neurosteroid pregnenolone reverts microtubule derangement induced by the loss of a functional CDKL5-IQGAP1 complex

CDKL5 is a protein kinase that plays a key role for neuronal functions as testified by the onset of complex neuronal dysfunctions in patients with genetic lesions in CDKL5. Here we identify a novel interactor of CDKL5, IQGAP1, a fundamental regulator of cell migration and polarity. In accordance with a functional role of this interaction, depletion of CDKL5 impairs cell migration and impedes the localization of IQGAP1 at the leading edge. Moreover, we demonstrate that CDKL5 is required for IQGAP1 to form a functional complex with its effectors, Rac1 and the microtubule plus end tracking protein CLIP170. These defects eventually impact on the microtubule association of CLIP170, thus deranging their dynamics. CLIP170 is a cellular target of the neurosteroid pregnenolone; by blocking CLIP170 in its active conformation, pregnenolone is capable of restoring the microtubule association of CLIP170 in CDKL5 deficient cells and rescuing morphological defects in neurons devoid of CDKL5. These findings provide novel insights into CDKL5 functions and pave the way for target-specific therapeutic strategies for individuals affected with CDKL5-disorder.

CDKL5 variants: Improving our understanding of a rare neurologic disorder

Objective:

To provide new insights into the interpretation of genetic variants in a rare neurologic disorder, CDKL5 deficiency, in the contexts of population sequencing data and an updated characterization of the CDKL5 gene.

Methods:

We analyzed all known potentially pathogenic CDKL5 variants by combining data from large-scale population sequencing studies with CDKL5 variants from new and all available clinical cohorts and combined this with computational methods to predict pathogenicity.

Results:

The study has identified several variants that can be reclassified as benign or likely benign. With the addition of novel CDKL5 variants, we confirm that pathogenic missense variants cluster in the catalytic domain of CDKL5 and reclassify a purported missense variant as having a splicing consequence. We provide further evidence that missense variants in the final 3 exons are likely to be benign and not important to disease pathology. We also describe benign splicing and nonsense variants within these exons, suggesting that isoform hCDKL5_5 is likely to have little or no neurologic significance. We also use the available data to make a preliminary estimate of minimum incidence of CDKL5 deficiency.

Conclusions:

These findings have implications for genetic diagnosis, providing evidence for the reclassification of specific variants previously thought to result in CDKL5 deficiency. Together, these analyses support the view that the predominant brain isoform in humans (hCDKL5_1) is crucial for normal neurodevelopment and that the catalytic domain is the primary functional domain.

Searching for biomarkers of CDKL5 disorder: early-onset visual impairment in CDKL5 mutant mice

CDKL5 disorder is a neurodevelopmental disorder still without a cure. Murine models of CDKL5 disorder have been recently generated raising the possibility of preclinical testing of treatments. However, unbiased, quantitative biomarkers of high translational value to monitor brain function are still missing. Moreover, the analysis of treatment is hindered by the challenge of repeatedly and non-invasively testing neuronal function. We analyzed the development of visual responses in a mouse model of CDKL5 disorder to introduce visually evoked responses as a quantitative method to assess cortical circuit function. Cortical visual responses were assessed in CDKL5 null male mice, heterozygous females, and their respective control wild-type littermates by repeated transcranial optical imaging from P27 until P32. No difference between wild-type and mutant mice was present at P25-P26 whereas defective responses appeared from P27-P28 both in heterozygous and homozygous CDKL5 mutant mice. These results were confirmed by visually evoked potentials (VEPs) recorded from the visual cortex of a different cohort. The previously imaged mice were also analyzed at P60-80 using VEPs, revealing a persistent reduction of response amplitude, reduced visual acuity and defective contrast function. The level of adult impairment was significantly correlated with the reduction in visual responses observed during development. Support vector machine showed that multi-dimensional visual assessment can be used to automatically classify mutant and wt mice with high reliability. Thus, monitoring visual responses represents a promising biomarker for preclinical and clinical studies on CDKL5 disorder.

RettBASE: Rett syndrome database update

Rett syndrome (RTT) is an X-linked progressive neurodevelopmental disorder that primarily affects females. Mutations in the MECP2 gene have been attributed as the major genetic cause of RTT. Recently, mutations in CDKL5 and FOXG1 genes have also been suggested to give rise to RTT, although subsequent more extensive studies suggest that diseases resulting from mutations in these two genes should be considered as distinct clinical entities. While the genetic basis for the RTT has been recognized, so far there is no effective cure for the disease and the treatments available are mainly aimed at ameliorating clinical problems associated with the disorder. The swift identification of the mutations in children is crucial for pursuing the best therapeutic care. RettBASE was created in 2002 as a MECP2 variant database and has grown to become a comprehensive variant database for RTT and related clinical phenotypes, containing a curated collection of variants for MECP2, CDKL5, and FOXG1 genes. Here, we describe the development and growth of RettBASE after its inception in 2001. Currently, RettBASE holds a total of 4,668 variants in MECP2, 498 variants in CDKL5, and 64 variants in FOXG1.

Further Clinical Delineation of the MEF2C Haploinsufficiency Syndrome: Report on New Cases and Literature Review of Severe Neurodevelopmental Disorders Presenting with Seizures, Absent Speech, and Involuntary Movements

Mutations in the MEF2C ( myocyte enhancer factor 2 ) gene have been established as a cause for an intellectual disability syndrome presenting with seizures, absence of speech, stereotypic movements, hypotonia, and limited ambulation. Phenotypic overlap with Rett's and Angelman's syndromes has been noted. Following the first reports of 5q14.3q15 microdeletions encompassing the MEF2C gene, further cases with point mutations and partial gene deletions of the MEF2C gene have been described. We present the clinical phenotype of our cohort of six patients with MEF2C mutations and compare our findings with previously reported patients as well as with a growing number of genetic conditions presenting with a severe neurodevelopmental, Rett-like, phenotype. We aim to add to the current knowledge of the natural history of the "MEF2C haploinsufficiency syndrome" as well as of the differential diagnosis, clinical management, and genetic counseling in this diagnostically challenging group of patients.

Unexplained Early Infantile Epileptic Encephalopathy in Han Chinese Children: Next-Generation Sequencing and Phenotype Enriching

Early Infantile Epileptic Encephalopathy (EIEE) presents shortly after birth with frequent, severe seizures and progressive disturbance of cerebral function. This study was to investigate a cohort of Chinese children with unexplained EIEE, infants with previous genetic diagnoses, causative brain malformations, or inborn errors of metabolism were excluded. We used targeted next-generation sequencing to identify potential pathogenic variants of 308 genes in 68 Han Chinese patients with unexplained EIEE. A filter process was performed to prioritize rare variants of potential functional significance. In all cases where parental testing was accessible, Sanger sequencing confirmed the variants and determined the parental origin. In 15% of patients (n = 10/68), we identified nine de novo pathogenic variants, and one assumed de novo pathogenic variant in the following genes: CDKL5 (n = 2), STXBP1 (n = 2), SCN1A (n = 3), KCNQ2 (n = 2), SCN8A (n = 1), four of the variants are novel variants. In 4% patients (n = 3/68), we identified three likely pathogenic variants; two assumed de novo and one X-linked in the following genes: SCN1A (n = 2) and ARX (n = 1), two of these variants are novel. Variants were assumed de novo when parental testing was not available. Our findings were first reported in Han Chinese patients with unexplained EIEE, enriching the EIEE mutation spectrum bank.

Amelioration of intractable epilepsy by adjunct vagus nerve stimulation therapy in a girl with a CDKL5 mutation

We report the case of on an 8-year-old girl with a cyclin-dependent kinase-like 5 mutation and who underwent vagus nerve stimulation (VNS) therapy for 2years. She had developed epilepsy at the age of 6months and had severe developmental delays. Initially, she had tonic and tonic-clonic seizures; however, around the age of 5years, she also developed epileptic spasms. These seizures were never completely controlled by conventional medical treatments. At the age of 7, after VNS initiation, her seizure frequency markedly reduced, and abnormal electrical activities on her electroencephalography tests strikingly decreased. Moreover, using questionnaires, we confirmed an improvement in her quality of life in the fields of alertness and activity. Although the efficacy of VNS therapy for patients with intractable epilepsy associated with a genetic anomaly has not been fully established, adjunctive VNS therapy may widen the scope of treatment choices available to these patients.

Identification of an elaborate complex mediating postsynaptic inhibition

Inhibitory synapses dampen neuronal activity through postsynaptic hyperpolarization. The composition of the inhibitory postsynapse and the mechanistic basis of its regulation, however, remain poorly understood. We used an in vivo chemico-genetic proximity-labeling approach to discover inhibitory postsynaptic proteins. Quantitative mass spectrometry not only recapitulated known inhibitory postsynaptic proteins but also revealed a large network of new proteins, many of which are either implicated in neurodevelopmental disorders or are of unknown function. Clustered regularly interspaced short palindromic repeats (CRISPR) depletion of one of these previously uncharacterized proteins, InSyn1, led to decreased postsynaptic inhibitory sites, reduced the frequency of miniature inhibitory currents, and increased excitability in the hippocampus. Our findings uncover a rich and functionally diverse assemblage of previously unknown proteins that regulate postsynaptic inhibition and might contribute to developmental brain disorders.

CDKL5 deficiency entails sleep apneas in mice

A recently discovered neurodevelopmental disorder caused by the mutation of the cyclin-dependent kinase-like 5 gene (CDKL5) entails complex autistic-like behaviours similar to Rett syndrome, but its impact upon physiological functions remains largely unexplored. Sleep-disordered breathing is common and potentially life-threatening in patients with Rett syndrome; however, evidence is limited in children with CDKL5 disorder, and is lacking altogether in adults. The aim of this study was to test whether the breathing pattern during sleep differs between adult Cdkl5 knockout (Cdkl5-KO) and wild-type (WT) mice. Using whole-body plethysmography, sleep and breathing were recorded non-invasively for 8 h during the light period. Sleep apneas occurred more frequently in Cdkl5-KO than in WT mice. A receiver operating characteristic (ROC) analysis discriminated Cdkl5-KO significantly from WT mice based on sleep apnea occurrence. These data demonstrate that sleep apneas are a core feature of CDKL5 disorder and a respiratory biomarker of CDKL5 deficiency in mice, and suggest that sleep-disordered breathing should be evaluated routinely in CDKL5 patients.

Heterozygous truncation mutations of the SMC1A gene cause a severe early onset epilepsy with cluster seizures in females: Detailed phenotyping of 10 new cases

OBJECTIVE

The phenotype of seizure clustering with febrile illnesses in infancy/early childhood is well recognized. To date the only genetic epilepsy consistently associated with this phenotype is PCDH19, an X-linked disorder restricted to females, and males with mosaicism. The SMC1A gene, which encodes a structural component of the cohesin complex is also located on the X chromosome. Missense variants and small in-frame deletions of SMC1A cause approximately 5% of Cornelia de Lange Syndrome (CdLS). Recently, protein truncating mutations in SMC1A have been reported in five females, all of whom have been affected by a drug-resistant epilepsy, and severe developmental impairment. Our objective was to further delineate the phenotype of SMC1A truncation.

METHOD

Female cases with de novo truncation mutations in SMC1A were identified from the Deciphering Developmental Disorders (DDD) study (n = 8), from postmortem testing of an affected twin (n = 1), and from clinical testing with an epilepsy gene panel (n = 1). Detailed information on the phenotype in each case was obtained.

RESULTS

Ten cases with heterozygous de novo mutations in the SMC1A gene are presented. All 10 mutations identified are predicted to result in premature truncation of the SMC1A protein. All cases are female, and none had a clinical diagnosis of CdLS. They presented with onset of epileptic seizures between <4 weeks and 28 months of age. In the majority of cases, a marked preponderance for seizures to occur in clusters was noted. Seizure clusters were associated with developmental regression. Moderate or severe developmental impairment was apparent in all cases.

SIGNIFICANCE

Truncation mutations in SMC1A cause a severe epilepsy phenotype with cluster seizures in females. These mutations are likely to be nonviable in males.

Molecular and genetic insights into an infantile epileptic encephalopathy - CDKL5 disorder

BACKGROUND

The discovery that mutations in cyclin-dependent kinase-like 5 (CDKL5) gene are associated with infantile epileptic encephalopathy has stimulated world-wide research effort to understand the molecular and genetic basis of CDKL5 disorder. Given the large number of literature published thus far, this review aims to summarize current genetic studies, draw a consensus on proposed molecular functions, and point to gaps of knowledge in CDKL5 research.

METHODS

A systematic review process was conducted using the PubMed search engine focusing on CDKL5 studies in the recent ten years. We analyzed these publications and summarized the findings into four sections: genetic studies, CDKL5 expression patterns, molecular functions, and animal models. We also discussed challenges and future directions in each section.

RESULTS

On the clinical side, CDKL5 disorder is characterized by early onset epileptic seizures, intellectual disability, and stereotypical behaviors. On the research side, a series of molecular and genetic studies in human patients, cell cultures and animal models have established the causality of CDKL5 to the infantile epileptic encephalopathy, and pointed to a key role for CDKL5 in regulating neuronal function in the brain. Mouse models of CDKL5 disorder have also been developed, and notably, manifest behavioral phenotypes, mimicking numerous clinical symptoms of CDKL5 disorder and advancing CDKL5 research to the preclinical stage.

CONCLUSIONS

Given what we have learned thus far, future identification of robust, quantitative, and sensitive outcome measures would be the key in animal model studies, particularly in heterozygous females. In the meantime, molecular and cellular studies of CDKL5 should focus on mechanism-based investigation and aim to uncover druggable targets that offer the potential to rescue or ameliorate CDKL5 disorder-related phenotypes.

Impacts of caring for a child with the CDKL5 disorder on parental wellbeing and family quality of life

Background

Although research in this area remains sparse, raising a child with some genetic disorders has been shown to adversely impact maternal health and family quality of life. The aim of this study was to investigate such impacts in families with a child with the CDKL5 disorder, a newly recognised genetic disorder causing severe neurodevelopmental impairments and refractory epilepsy.

Methods

Data were sourced from the International CDKL5 Disorder Database to which 192 families with a child with a pathogenic CDKL5 mutation had provided data by January 2016. The Short Form 12 Health Survey Version 2, yielding a Physical Component Summary and a Mental Component Summary score, was used to measure primary caregiver’s wellbeing. The Beach Center Family Quality of Life Scale was used to measure family quality of life. Linear regression analyses were used to investigate relationships between child and family factors and the various subscale scores.

Results

The median (range) age of the primary caregivers was 37.0 (24.6–63.7) years and of the children was 5.2 (0.2–34.1) years. The mean (SD) physical and mental component scores were 53.7 (8.6) and 41.9 (11.6), respectively. In mothers aged 25–54 years the mean mental but not the physical component score was lower than population norms. After covariate adjustment, caregivers with a tube-fed child had lower mean physical but higher mean mental component scores than those whose child fed orally (coefficient = −4.80 and 6.79; p = 0.009 and 0.012, respectively). Child sleep disturbances and financial hardship were negatively associated with the mental component score. The mean (SD) Beach Center Family Quality of Life score was 4.06 (0.66) and those who had used respite services had lower scores than those who had not across the subscales.

Conclusions

Emotional wellbeing was considerably impaired in this caregiver population, and was particularly associated with increased severity of child sleep problems and family financial difficulties. Family quality of life was generally rated lowest in those using respite care extensively, suggesting that these families may be more burdened by daily caregiving.

Clinical and biological progress over 50 years in Rett syndrome

In the 50 years since Andreas Rett first described the syndrome that came to bear his name, and is now known to be caused by a mutation in the methyl-CpG-binding protein 2 (MECP2) gene, a compelling blend of astute clinical observations and clinical and laboratory research has substantially enhanced our understanding of this rare disorder. Here, we document the contributions of the early pioneers in Rett syndrome (RTT) research, and describe the evolution of knowledge in terms of diagnostic criteria, clinical variation, and the interplay with other Rett-related disorders. We provide a synthesis of what is known about the neurobiology of MeCP2, considering the lessons learned from both cell and animal models, and how they might inform future clinical trials. With a focus on the core criteria, we examine the relationships between genotype and clinical severity. We review current knowledge about the many comorbidities that occur in RTT, and how genotype may modify their presentation. We also acknowledge the important drivers that are accelerating this research programme, including the roles of research infrastructure, international collaboration and advocacy groups. Finally, we highlight the major milestones since 1966, and what they mean for the day-to-day lives of individuals with RTT and their families.

Seizure variables and their relationship to genotype and functional abilities in the CDKL5 disorder

OBJECTIVE

To investigate seizure outcomes and their relationships to genotype and functional abilities in individuals with the cyclin-dependent kinase-like-5 (CDKL5) disorder.

METHODS

Using the International CDKL5 Disorder Database, we identified 172 cases with a pathogenic CDKL5 mutation. We categorized individual mutations into 4 groups based on predicted structural and functional consequences. Negative binomial regression was used to model the linear association between current seizure rate and mutation group, current level of assistance required to walk 10 steps, and the highest level of expressive communication used to convey refusal or request.

RESULTS

All but 3 (169/172) patients had a history of epilepsy. The median age at seizure onset was 6 weeks (range 1 week-1.5 years) and the median seizure rate at ascertainment was 2 per day (range 0-20 per day). After adjusting for walking ability and confounders including use or otherwise of polytherapy, seizure rate was lower in those with truncating mutations between aa172 and aa781 compared to those with no functional protein (incidence rate ratio [IRR] 0.57; 95% confidence interval [CI] 0.35-0.93). Ability to walk and use of spoken language were associated with lower rates of current seizures when compared to those with the least ability after adjusting for genotype (walking: IRR 0.62; 95% CI 0.39-0.99, communication: IRR 0.48; 95% CI 0.23-1.02). At a median age at questionnaire completion of 5 years, those previously treated with corticosteroids had more frequent seizures than those who have never been treated, whether or not there was a history of infantile spasms.

CONCLUSIONS

Epilepsy is pervasive but not mandatory for the CDKL5 disorder. Genotype and functional abilities were related to seizure frequency, which appears refractory to antiepileptic drugs.

Rett syndrome: a wide clinical and autonomic picture

Background

Rett Syndrome is a neurodevelopmental disorder almost exclusively affecting females, characterized by a broad clinical spectrum of signs and symptoms and a peculiar course. The disease affects different body systems: nervous, muscolo-skeletal, gastro-enteric. Moreover, part of the symptoms are related to the involvement of the autonomic nervous system.

In the Tuscany Rett Center at Versilia Hospital, we collected data from 151 subjects with a clinical diagnosis of classical or variant RTT syndrome. For each subject, we assessed the severity of the condition with clinical-rating scales (ISS, PBZ), we quantified the performance of the autonomic nervous system, and we performed genetic analysis. We used multivariate statistical analysis of the data to evaluate the relation between the different clinical RTT forms, the cardiorespiratory phenotype, the different genetic mutations and the severity of the clinical picture. Individuals were classified according to existing forms: Classical RTT and three atypical RTT: Z-RTT, Hanefeld, Congenital. A correlation between C-Terminal deletions and lower severity of the clinical manifestations was evident, in the previous literature, but, considering the analysis of autonomic behaviour, the original classification can be enriched with a more accurate subdivision of Rett subgroups, which may be useful for early diagnosis.

Results

Present data emphasize some differences, not entirely described in the literature, among RTT variants. In our cohort the Z-RTT variant cases show clinical features (communication, growth, epilepsy and development), well documented by specific ISS items, less severe, if compared to classical RTT and show autonomic disorders, previously not reported in the literature. In this form epilepsy is rarely present. In contrast, Hanefeld variant shows the constant presence of epilepsy which has an earlier onset In Hanefeld variant the frequency of apneas was rare and, among the cardiorespiratory phenotypes, the feeble type is lacking.

Conclusion

A quantitative analysis of the different autonomic components reveals differences across typical and atypical forms of RTT that leads to a more accurate classification of the groups. In our cohort of RTT individuals, the inclusion of autonomic parameter in the classification leads to an improved diagnosis at earlier stages of development.

HDAC4: a key factor underlying brain developmental alterations in CDKL5 disorder

Cyclin-dependent kinase-like 5 (CDKL5) is a Ser/Thr protein kinase predominantly expressed in the brain. Mutations of the CDKL5 gene lead to CDKL5 disorder, a neurodevelopmental pathology that shares several features with Rett Syndrome and is characterized by severe intellectual disability. The phosphorylation targets of CDKL5 are largely unknown, which hampers the discovery of therapeutic strategies for improving the neurological phenotype due to CDKL5 mutations. Here, we show that the histone deacetylase 4 (HDAC4) is a direct phosphorylation target of CDKL5 and that CDKL5-dependent phosphorylation promotes HDAC4 cytoplasmic retention. Nuclear HDAC4 binds to chromatin as well as to MEF2A transcription factor, leading to histone deacetylation and altered neuronal gene expression. By using a Cdkl5 knockout (Cdkl5 -/Y) mouse model, we found that hypophosphorylated HDAC4 translocates to the nucleus of neural precursor cells, thereby reducing histone 3 acetylation. This effect was reverted by re-expression of CDKL5 or by inhibition of HDAC4 activity through the HDAC4 inhibitor LMK235. In Cdkl5 -/Y mice treated with LMK235, defective survival and maturation of neuronal precursor cells and hippocampus-dependent memory were fully normalized. These results demonstrate a critical role of HDAC4 in the neurodevelopmental alterations due to CDKL5 mutations and suggest the possibility of HDAC4-targeted pharmacological interventions.

Characterisation of CDKL5 Transcript Isoforms in Human and Mouse

Mutations in the X-linked Cyclin-Dependent Kinase-Like 5 gene (CDKL5) cause early onset infantile spasms and subsequent severe developmental delay in affected children. Deleterious mutations have been reported to occur throughout the CDKL5 coding region. Several studies point to a complex CDKL5 gene structure in terms of exon usage and transcript expression. Improvements in molecular diagnosis and more extensive research into the neurobiology of CDKL5 and pathophysiology of CDKL5 disorders necessitate an updated analysis of the gene. In this study, we have analysed human and mouse CDKL5 transcript patterns both bioinformatically and experimentally. We have characterised the predominant brain isoform of CDKL5, a 9.7 kb transcript comprised of 18 exons with a large 6.6 kb 3’-untranslated region (UTR), which we name hCDKL5_1. In addition we describe new exonic regions and a range of novel splice and UTR isoforms. This has enabled the description of an updated gene model in both species and a standardised nomenclature system for CDKL5 transcripts. Profiling revealed tissue- and brain development stage-specific differences in expression between transcript isoforms. These findings provide an essential backdrop for the diagnosis of CDKL5-related disorders, for investigations into the basic biology of this gene and its protein products, and for the rational design of gene-based and molecular therapies for these disorders.

Prevalence and onset of comorbidities in the CDKL5 disorder differ from Rett syndrome

Background

Initially described as an early onset seizure variant of Rett syndrome, the CDKL5 disorder is now considered as an independent entity. However, little is currently known about the full spectrum of comorbidities that affect these patients and available literature is limited to small case series. This study aimed to use a large international sample to examine the prevalence in this disorder of comorbidities of epilepsy, gastrointestinal problems including feeding difficulties, sleep and respiratory problems and scoliosis and their relationships with age and genotype. Prevalence and onset were also compared with those occurring in Rett syndrome.

Methods

Data for the CDKL5 disorder and Rett syndrome were sourced from the International CDKL5 Disorder Database (ICDD), InterRett and the Australian Rett syndrome Database (ARSD). Logistic regression (multivariate and univariate) was used to analyse the relationships between age group, mutation type and the prevalence of various comorbidities. Binary longitudinal data from the ARSD and the equivalent cross-sectional data from ICDD were examined using generalized linear models with generalized estimating equations. The Kaplan-Meier method was used to estimate the failure function for the two disorders and the log-rank test was used to compare the two functions.

Results

The likelihood of experiencing epilepsy, GI problems, respiratory problems, and scoliosis in the CDKL5 disorder increased with age and males were more vulnerable to respiratory and sleep problems than females. We did not identify any statistically significant relationships between mutation group and prevalence of comorbidities. Epilepsy, GI problems and sleep abnormalities were more common in the CDKL5 disorder than in Rett syndrome whilst scoliosis and respiratory problems were less prevalent.

Conclusion

This study captured a much clearer picture of the CDKL5 disorder than previously possible using the largest sample available to date. There were differences in the presentation of clinical features occurring in the CDKL5 disorder and in Rett syndrome, reinforcing the concept that CDKL5 is an independent disorder with its own distinctive characteristics.

The genetics of the epilepsies

While genetic causes of epilepsy have been hypothesized from the time of Hippocrates, the advent of new genetic technologies has played a tremendous role in elucidating a growing number of specific genetic causes for the epilepsies. This progress has contributed vastly to our recognition of the epilepsies as a diverse group of disorders, the genetic mechanisms of which are heterogeneous. Genotype-phenotype correlation, however, is not always clear. Nonetheless, the developments in genetic diagnosis raise the promise of a future of personalized medicine. Multiple genetic tests are now available, but there is no one test for all possible genetic mutations, and the balance between cost and benefit must be weighed. A genetic diagnosis, however, can provide valuable information regarding comorbidities, prognosis, and even treatment, as well as allow for genetic counseling. In this review, we will discuss the genetic mechanisms of the epilepsies as well as the specifics of particular genetic epilepsy syndromes. We will include an overview of the available genetic testing methods, the application of clinical knowledge into the selection of genetic testing, genotype-phenotype correlations of epileptic disorders, and therapeutic advances as well as a discussion of the importance of genetic counseling.

Improving diagnosis and broadening the phenotypes in early-onset seizure and severe developmental delay disorders through gene panel analysis

Background

We sought to investigate the diagnostic yield and mutation spectrum in previously reported genes for early-onset epilepsy and disorders of severe developmental delay.

Methods

In 400 patients with these disorders with no known underlying aetiology and no major structural brain anomaly, we analysed 46 genes using a combination of targeted sequencing on an Illumina MiSeq platform and targeted, exon-level microarray copy number analysis.

Results

We identified causative mutations in 71/400 patients (18%). The diagnostic rate was highest among those with seizure onset within the first two months of life (39%), although overall it was similar in those with and without seizures. The most frequently mutated gene was SCN2A (11 patients, 3%). Other recurrently mutated genes included CDKL5, KCNQ2, SCN8A (six patients each), FOXG1, MECP2, SCN1A, STXBP1 (five patients each), KCNT1, PCDH19, TCF4 (three patients each) and ATP1A3, PRRT2 and SLC9A6 (two patients each). Mutations in EHMT1, GABRB3, LGI1, MBD5, PIGA, UBE3A and ZEB2 were each found in single patients. We found mutations in a number of genes in patients where either the electroclinical features or dysmorphic phenotypes were atypical for the identified gene. In only 11 cases (15%) had the clinician sufficient certainty to specify the mutated gene as the likely cause before testing.

Conclusions

Our data demonstrate the considerable utility of a gene panel approach in the diagnosis of patients with early-onset epilepsy and severe developmental delay disorders., They provide further insights into the phenotypic spectrum and genotype–phenotype correlations for a number of the causative genes and emphasise the value of exon-level copy number testing in their analysis.

CDKL5 and Shootin1 Interact and Concur in Regulating Neuronal Polarization

In the last years, the X-linked cyclin-dependent kinase-like 5 (CDKL5) gene has been associated with epileptic encephalopathies characterized by the early onset of intractable epilepsy, severe developmental delay, autistic features, and often the development of Rett syndrome-like features. Still, the role of CDKL5 in neuronal functions is not fully understood. By way of a yeast two hybrid screening we identified the interaction of CDKL5 with shootin1, a brain specific protein acting as a determinant of axon formation during neuronal polarization. We found evidence that CDKL5 is involved, at least in part, in regulating neuronal polarization through its interaction with shootin1. Indeed, the two proteins interact in vivo and both are localized in the distal tip of outgrowing axons. By using primary hippocampal neurons as model system we find that adequate CDKL5 levels are required for axon specification. In fact, a significant number of neurons overexpressing CDKL5 is characterized by supernumerary axons, while the silencing of CDKL5 disrupts neuronal polarization. Interestingly, shootin1 phosphorylation is reduced in neurons silenced for CDKL5 suggesting that the kinase affects, directly or indirectly, the post-translational modification of shootin1. Finally, we find that the capacity of CDKL5 to generate surplus axons is attenuated in neurons with reduced shootin1 levels, in agreement with the notion that two proteins act in a common pathway. Altogether, these results point to a role of CDKL5 in the early steps of neuronal differentiation that can be explained, at least in part, by its association with shootin1.

Retrospective evaluation of low long-term efficacy of antiepileptic drugs and ketogenic diet in 39 patients with CDKL5-related epilepsy

OBJECTIVE

Mutations in the CDKL5 gene cause an early-onset epileptic encephalopathy. To date, little is known about effective antiepileptic treatment in this disorder.

METHOD

Accordingly, the aim of this retrospective study was to explore the role of different antiepileptic drugs (AEDs) and the ketogenic diet (KD) in the treatment of this rare genetic disorder. We evaluated the efficacy in 39 patients with CDKL5 mutations at 3, 6 and 12 months after the introduction of each treatment. One patient was lost to follow-up after 6 and 12 months.

RESULTS

The responder rate (>50% reduction in seizure frequency) to at least one AED or KD was 69% (27/39) after 3 months, 45% (17/38) after 6 months and 24% (9/38) after 12 months. The highest rate of seizure reduction after 3 months was reported for FBM (3/3), VGB (8/25), CLB (4/17), VPA (7/34), steroids (5/26), LTG (5/23) and ZNS (2/11). Twelve patients (31%) experienced a seizure aggravation to at least one AED. Most patients showed some but only initial response to various AEDs with different modes of actions.

SIGNIFICANCE

Considering both age-related and spontaneous fluctuation in seizure frequency and the unknown impact of many AEDs or KD on cognition, our data may help defining realistic treatment goals and avoiding overtreatment in patients with CDKL5 mutations. There is a strong need to develop new treatment strategies for patients with this rare mutation.

Neurobehavioral phenotype in cyclin-dependent kinase-like 5 syndrome: Case report and review of literature

The phenotype of cyclin-dependent kinase-like 5 (CDKL5) syndrome includes Rett syndrome variant with early onset seizures, early onset epileptic encephalopathy; and severe developmental delay. Autistic features have often been reported in literature, but detailed reports of the behavior of these individuals are lacking. We describe the clinical picture of a girl aged 15 years 9 months affected by CDKL5 syndrome, with special attention to the neurobehavioral phenotype. The evaluation showed, apart from a profound intellectual disability, the presence of atypical features of behavior, mainly in relating to people, in imitation, and in verbal and nonverbal communication, thus justifying the diagnosis of comorbid autism spectrum disorder. A formal assessment of the behavior, through appropriate tools, is necessary to choose the most appropriate rehabilitative intervention and to characterize in more detail the CDKL5 syndrome phenotype. We propose a testing protocol for the neurobehavioral assessment of these patients.

Two Siblings With a CDKL5 Mutation: Genotype and Phenotype Evaluation

This is the second report of a family with a recurrence of a CDKL5 mutation (c. 283-3_290del) in 2 sisters. Both parents tested negative for the mutation in all tissues, but germline mosaicism is likely. Clinically CDKL5 patients resemble those with Rett syndrome, caused by a MECP2 mutation, who experience a regression, after an initial normal development. Even though both siblings showed a typical CDKL5 phenotype, their presentation is different. From birth, the oldest daughter had a severe developmental delay, feeding problems, and hypotonia and experienced daily refractory seizures. The youngest daughter appeared to be normal until age 3 months. At that age seizures started, deterioration and regression became evident, and an epileptic encephalopathy developed. This report of familial recurrence, with suspected germline mosaicism in a healthy parent, has important consequences for genetic counseling. Although it is not possible to predict an exact recurrence risk, it is likely to be increased.

[Molecular basis of Rett syndrome: A current look]

Rett syndrome (RS) is a neurodevelopmental disorder that exclusively affects girls, and occurs along with autism. It is very uncommon, and has five distinct forms, one classic and the others atypical, which generally compromise manual skills, language, and mobility, and widely associated with the appearance of stereotypy and early epilepsy. With the aim of updating the information about RS, a search was performed in the computer data bases of PubMed, Hinari, SCIELO and Medline, as well as consulting other web sites including OMIM, ORPHANET, GeneMap, Genetests, Proteins and Gene, using the descriptors "Síndrome de Rett", "genes y Síndrome de Rett", "Rett Syndrome gene", "Rett Syndrome", "Rett Syndrome gene therapy", and "Rett Syndrome review". Of the 1,348 articles found, 42 articles were selected, which reported 3 genes causing the syndrome: MECP2, CDKL5 and FOXG. The MECP2 gene is mutated in 80% of patients with classic RS, as well as in 40% of those affected by any of its atypical forms. RS with early epilepsy and the congenital variant are mainly due to variations in the CDKL5 and FOXG1 genes, respectively.

CONCLUSIONS

The diagnosis of RS is based on clinical criteria. However, the advances in molecular biology and genetics have opened a wide range of possibilities for diagnosing the different clinical forms that could not be classified before. Molecular analysis can help confirm the clinical criteria and provided information as regards the prognosis of the patient.

The Utility of Next-Generation Sequencing in Gene Discovery for Mutation-Negative Patients with Rett Syndrome

Rett syndrome (RTT) is a rare, severe disorder of neuronal plasticity that predominantly affects girls. Girls with RTT usually appear asymptomatic in the first 6–18 months of life, but gradually develop severe motor, cognitive, and behavioral abnormalities that persist for life. A predominance of neuronal and synaptic dysfunction, with altered excitatory–inhibitory neuronal synaptic transmission and synaptic plasticity, are overarching features of RTT in children and in mouse models. Over 90% of patients with classical RTT have mutations in the X-linked methyl-CpG-binding (MECP2) gene, while other genes, including cyclin-dependent kinase-like 5 (CDKL5), Forkhead box protein G1 (FOXG1), myocyte-specific enhancer factor 2C (MEF2C), and transcription factor 4 (TCF4), have been associated with phenotypes overlapping with RTT. However, there remain a proportion of patients who carry a clinical diagnosis of RTT, but who are mutation negative. In recent years, next-generation sequencing technologies have revolutionized approaches to genetic studies, making whole-exome and even whole-genome sequencing possible strategies for the detection of rare and de novo mutations, aiding the discovery of novel disease genes. Here, we review the recent progress that is emerging in identifying pathogenic variations, specifically from exome sequencing in RTT patients, and emphasize the need for the use of this technology to identify known and new disease genes in RTT patients.

Cytokine Dysregulation in MECP2- and CDKL5-Related Rett Syndrome: Relationships with Aberrant Redox Homeostasis, Inflammation, and ω-3 PUFAs

An involvement of the immune system has been suggested in Rett syndrome (RTT), a devastating neurodevelopmental disorder related to oxidative stress, and caused by a mutation in the methyl-CpG binding protein 2 gene (MECP2) or, more rarely, cyclin-dependent kinase-like 5 (CDKL5). To date, it is unclear whether both mutations may have an impact on the circulating cytokine patterns. In the present study, cytokines involved in the Th1-, Th2-, and T regulatory (T-reg) response, as well as chemokines, were investigated in MECP2- (MECP2-RTT) (n = 16) and CDKL5-Rett syndrome (CDKL5-RTT) (n = 8), before and after ω-3 polyunsaturated fatty acids (PUFAs) supplementation. A major cytokine dysregulation was evidenced in untreated RTT patients. In MECP2-RTT, a Th2-shifted balance was evidenced, whereas in CDKL5-RTT both Th1- and Th2-related cytokines (except for IL-4) were upregulated. In MECP2-RTT, decreased levels of IL-22 were observed, whereas increased IL-22 and T-reg cytokine levels were evidenced in CDKL5-RTT. Chemokines were unchanged. The cytokine dysregulation was proportional to clinical severity, inflammatory status, and redox imbalance. Omega-3 PUFAs partially counterbalanced cytokine changes, as well as aberrant redox homeostasis and the inflammatory status. RTT is associated with a subclinical immune dysregulation as the likely consequence of a defective inflammation regulatory signaling system.

Inhibition of GSK3β rescues hippocampal development and learning in a mouse model of CDKL5 disorder

Mutations in the X-linked cyclin-dependent kinase-like 5 (CDKL5) gene have been identified in a rare neurodevelopmental disorder characterized by early-onset seizures, severe developmental delay, intellectual disability and Rett syndrome-like features. CDKL5 is highly expressed in the brain during early postnatal stages, suggesting its importance for brain maturation. Using a newly-generated Cdkl5 knockout (Cdkl5 -/Y) mouse, we recently found that loss of Cdkl5 impairs postnatal hippocampal development with a reduction in neuronal precursor survival and maturation. These defects were accompanied by increased activity of the glycogen synthase kinase 3β (GSK3β) a crucial inhibitory regulator of many neurodevelopmental processes. The goal of the current study was to establish whether inhibition of GSK3β corrects hippocampal developmental defects due to Cdkl5 loss. We found that treatment with the GSK3β inhibitor SB216763 restored neuronal precursor survival, dendritic maturation, connectivity and hippocampus-dependent learning and memory in the Cdkl5 -/Y mouse. Importantly, these effects were retained one month after treatment cessation. At present, there are no therapeutic strategies to improve the neurological defects of subjects with CDKL5 disorder. Current results point at GSK3β inhibitors as potential therapeutic tools for the improvement of abnormal brain development in CDKL5 disorder.

Sequential Elution Interactome Analysis of the Mind Bomb 1 Ubiquitin Ligase Reveals a Novel Role in Dendritic Spine Outgrowth

The mind bomb 1 (Mib1) ubiquitin ligase is essential for controlling metazoan development by Notch signaling and possibly the Wnt pathway. It is also expressed in postmitotic neurons and regulates neuronal morphogenesis and synaptic activity by mechanisms that are largely unknown. We sought to comprehensively characterize the Mib1 interactome and study its potential function in neuron development utilizing a novel sequential elution strategy for affinity purification, in which Mib1 binding proteins were eluted under different stringency and then quantified by the isobaric labeling method. The strategy identified the Mib1 interactome with both deep coverage and the ability to distinguish high-affinity partners from low-affinity partners. A total of 817 proteins were identified during the Mib1 affinity purification, including 56 high-affinity partners and 335 low-affinity partners, whereas the remaining 426 proteins are likely copurified contaminants or extremely weak binding proteins. The analysis detected all previously known Mib1-interacting proteins and revealed a large number of novel components involved in Notch and Wnt pathways, endocytosis and vesicle transport, the ubiquitin-proteasome system, cellular morphogenesis, and synaptic activities. Immunofluorescence studies further showed colocalization of Mib1 with five selected proteins: the Usp9x (FAM) deubiquitinating enzyme, alpha-, beta-, and delta-catenins, and CDKL5. Mutations of CDKL5 are associated with early infantile epileptic encephalopathy-2 (EIEE2), a severe form of mental retardation. We found that the expression of Mib1 down-regulated the protein level of CDKL5 by ubiquitination, and antagonized CDKL5 function during the formation of dendritic spines. Thus, the sequential elution strategy enables biochemical characterization of protein interactomes; and Mib1 analysis provides a comprehensive interactome for investigating its role in signaling networks and neuronal development.

Mutations in epilepsy and intellectual disability genes in patients with features of Rett syndrome

Rett syndrome and neurodevelopmental disorders with features overlapping this syndrome frequently remain unexplained in patients without clinically identified MECP2 mutations. We recruited a cohort of 11 patients with features of Rett syndrome and negative initial clinical testing for mutations in MECP2. We analyzed their phenotypes to determine whether patients met formal criteria for Rett syndrome, reviewed repeat clinical genetic testing, and performed exome sequencing of the probands. Using 2010 diagnostic criteria, three patients had classical Rett syndrome, including two for whom repeat MECP2 gene testing had identified mutations. In a patient with neonatal onset epilepsy with atypical Rett syndrome, we identified a frameshift deletion in STXBP1. Among seven patients with features of Rett syndrome not fulfilling formal diagnostic criteria, four had suspected pathogenic mutations, one each in MECP2, FOXG1, SCN8A, and IQSEC2. MECP2 mutations are highly correlated with classical Rett syndrome. Genes associated with atypical Rett syndrome, epilepsy, or intellectual disability should be considered in patients with features overlapping with Rett syndrome and negative MECP2 testing. While most of the identified mutations were apparently de novo, the SCN8A variant was inherited from an unaffected parent mosaic for the mutation, which is important to note for counseling regarding recurrence risks.

Integrated analysis of whole-exome sequencing and transcriptome profiling in males with autism spectrum disorders

BACKGROUND

Autism spectrum disorders (ASD) are a group of neurodevelopmental disorders with high heritability. Recent findings support a highly heterogeneous and complex genetic etiology including rare de novo and inherited mutations or chromosomal rearrangements as well as double or multiple hits.

METHODS

We performed whole-exome sequencing (WES) and blood cell transcriptome by RNAseq in a subset of male patients with idiopathic ASD (n = 36) in order to identify causative genes, transcriptomic alterations, and susceptibility variants.

RESULTS

We detected likely monogenic causes in seven cases: five de novo (SCN2A, MED13L, KCNV1, CUL3, and PTEN) and two inherited X-linked variants (MAOA and CDKL5). Transcriptomic analyses allowed the identification of intronic causative mutations missed by the usual filtering of WES and revealed functional consequences of some rare mutations. These included aberrant transcripts (PTEN, POLR3C), deregulated expression in 1.7% of mutated genes (that is, SEMA6B, MECP2, ANK3, CREBBP), allele-specific expression (FUS, MTOR, TAF1C), and non-sense-mediated decay (RIT1, ALG9). The analysis of rare inherited variants showed enrichment in relevant pathways such as the PI3K-Akt signaling and the axon guidance.

CONCLUSIONS

Integrative analysis of WES and blood RNAseq data has proven to be an efficient strategy to identify likely monogenic forms of ASD (19% in our cohort), as well as additional rare inherited mutations that can contribute to ASD risk in a multifactorial manner. Blood transcriptomic data, besides validating 88% of expressed variants, allowed the identification of missed intronic mutations and revealed functional correlations of genetic variants, including changes in splicing, expression levels, and allelic expression.

CDKL5 variant in a boy with infantile epileptic encephalopathy: case report

A Chinese boy presented at 18 months with intractable epilepsy, developmental delay and autistic features. He had multiple seizure types, including absence, myoclonic seizures, limb spasm and tonic seizures. His seizures were finally controlled at 3 years of age with clonazepam and a short course of chloral hydrate incidentally given for his insomnia. Subsequently, he had improvement in his communication skills.

RESULT

A novel hemizygous missense variant (c.1649G>A; p.R550Q) in exon 12 of CDKL5 gene was detected for him, his asymptomatic mother and elder sister. His phenotype is less severe than other male cases.

CONCLUSION

We recommend screening CDKL5 for boys with pharmarco-resistant epilepsy and a trial of benzodiazepines for Infantile Epileptic Encephalopathy (IEE).

FOXG1 Mutation is a Low-Incidence Genetic Cause in Atypical Rett Syndrome

Due to the genetic and clinical heterogeneity of Rett syndrome, patients with nonclassic phenotypes are classified as an atypical Rett syndrome, that is, preserved speech variant, early seizure variant, and congenital variant. Respectively, MECP2, CDKL5, and FOXG1 have been found to be the causative genes, but FOXG1 variants are the rarest and least studied. We performed mutational analyses for FOXG1 on 11 unrelated patients without MECP2 and CDKL5 mutations, who were diagnosed with atypical Rett syndrome. One patient, who suffered from severe early-onset mental retardation and multiple-type intractable seizures, carried a novel, de novo FOXG1 mutation (p.Gln70Pro). This case concurs with previous studies that have reported yields of ∼10%. FOXG1-related atypical Rett syndrome is rare in Korean population, but screening of this gene in patients with severe mental retardation, microcephaly, and early-onset multiple seizure types without specific genetic causes can help broaden the phenotypic spectrum of the distinct FOXG1-related syndrome.

There is variability in the attainment of developmental milestones in the CDKL5 disorder

Background

Individuals with the CDKL5 disorder have been described as having severely impaired development. A few individuals have been reported having attained more milestones including walking and running. Our aim was to investigate variation in attainment of developmental milestones and associations with underlying genotype.

Methods

Data was sourced from the International CDKL5 Disorder Database, and individuals were included if they had a pathogenic or probably pathogenic CDKL5 mutation and information on early development. Kaplan-Meier time-to-event analyses investigated the occurrence of developmental milestones. Mutations were grouped by their structural/functional consequence, and Cox regression was used to investigate the relationship between genotype and milestone attainment.

Results

The study included 109 females and 18 males. By 5 years of age, only 75% of the females had attained independent sitting and 25% independent walking whilst a quarter of the males could sit independently by 1 year 3 months. Only one boy could walk independently. No clear relationship between mutation group and milestone attainment was present, although females with a late truncating mutation attained the most milestones.

Conclusion

Attainment of developmental milestones is severely impaired in the CDKL5 disorder, with the majority who did attain skills attaining them at a late age. It appears as though males are more severely impaired than the females. Larger studies are needed to further investigate the role of genotype on clinical variability.

If not Angelman, what is it? A review of Angelman-like syndromes

Angelman syndrome (AS) is caused by a lack of expression of the maternally inherited UBE3A gene in the brain. However, about 10% of individuals with a clinical diagnosis of AS do not have an identifiable molecular defect. It is likely that most of those individuals have an AS-like syndrome that is clinically and molecularly distinct from AS. These AS-like syndromes can be broadly classified into chromosomal microdeletion and microduplication syndromes, and single-gene disorders. The microdeletion/microduplication syndromes are now easily identified by chromosomal microarray analysis and include Phelan–McDermid syndrome (chromosome 22q13.3 deletion), MBD5 haploinsufficiency syndrome (chromosome 2q23.1 deletion), and KANSL1 haploinsufficiency syndrome (chromosome 17q21.31 deletion). The single-gene disorders include Pitt–Hopkins syndrome (TCF4), Christianson syndrome (SLC9A6), Mowat–Wilson syndrome (ZEB2), Kleefstra syndrome (EHMT1), and Rett (MECP2) syndrome. They also include disorders due to mutations in HERC2, adenylosuccinase lyase (ADSL), CDKL5, FOXG1, MECP2 (duplications), MEF2C, and ATRX. Although many of these single-gene disorders can be caused by chromosomal microdeletions resulting in haploinsufficiency of the critical gene, the individual disorders are often caused by intragenic mutations that cannot be detected by chromosomal microarray analysis. We provide an overview of the clinical features of these syndromes, comparing and contrasting them with AS, in the hope that it will help guide clinicians in the diagnostic work-up of individuals with AS-like syndromes.

Deletion of protein tyrosine phosphatase, non-receptor type 4 (PTPN4) in twins with a Rett syndrome-like phenotype

Rett syndrome (RTT), a neurodevelopmental disorder that predominantly affects females, is primarily caused by variants in MECP2. Variants in other genes such as CDKL5 and FOXG1 are usually associated with individuals who manifest distinct phenotypes that may overlap with RTT. Individuals with phenotypes suggestive of RTT are typically screened for variants in MECP2 and then subsequently the other genes dependent on the specific phenotype. Even with this screening strategy, there are individuals in whom no causative variant can be identified, suggesting that there are other novel genes that contribute to the RTT phenotype. Here we report a de novo deletion of protein tyrosine phosphatase, non-receptor type 4 (PTPN4) in identical twins with a RTT-like phenotype. We also demonstrate the reduced expression of Ptpn4 in a Mecp2 null mouse model of RTT, as well as the activation of the PTPN4 promoter by MeCP2. Our findings suggest that PTPN4 should be considered for addition to the growing list of genes that warrant screening in individuals with a RTT-like phenotype.

Genetic forms of epilepsies and other paroxysmal disorders

Genetic mechanisms explain the pathophysiology of many forms of epilepsy and other paroxysmal disorders, such as alternating hemiplegia of childhood, familial hemiplegic migraine, and paroxysmal dyskinesias. Epilepsy is a key feature of well-defined genetic syndromes including tuberous sclerosis complex, Rett syndrome, Angelman syndrome, and others. There is an increasing number of single-gene causes or susceptibility factors associated with several epilepsy syndromes, including the early-onset epileptic encephalopathies, benign neonatal/infantile seizures, progressive myoclonus epilepsies, genetic generalized and benign focal epilepsies, epileptic aphasias, and familial focal epilepsies. Molecular mechanisms are diverse, and a single gene can be associated with a broad range of phenotypes. Additional features, such as dysmorphisms, head size, movement disorders, and family history may provide clues to a genetic diagnosis. Genetic testing can impact medical care and counseling. We discuss genetic mechanisms of epilepsy and other paroxysmal disorders, tools and indications for genetic testing, known genotype-phenotype associations, the importance of genetic counseling, and a look toward the future of epilepsy genetics.

Mapping pathological phenotypes in a mouse model of CDKL5 disorder

Mutations in cyclin-dependent kinase-like 5 (CDKL5) cause early-onset epileptic encephalopathy, a neurodevelopmental disorder with similarities to Rett Syndrome. Here we describe the physiological, molecular, and behavioral phenotyping of a Cdkl5 conditional knockout mouse model of CDKL5 disorder. Behavioral analysis of constitutive Cdkl5 knockout mice revealed key features of the human disorder, including limb clasping, hypoactivity, and abnormal eye tracking. Anatomical, physiological, and molecular analysis of the knockout uncovered potential pathological substrates of the disorder, including reduced dendritic arborization of cortical neurons, abnormal electroencephalograph (EEG) responses to convulsant treatment, decreased visual evoked responses (VEPs), and alterations in the Akt/rpS6 signaling pathway. Selective knockout of Cdkl5 in excitatory and inhibitory forebrain neurons allowed us to map the behavioral features of the disorder to separable cell-types. These findings identify physiological and molecular deficits in specific forebrain neuron populations as possible pathological substrates in CDKL5 disorder.

Clinical features and gene mutational spectrum of CDKL5-related diseases in a cohort of Chinese patients

BACKGROUND

Mutations in the cyclin-dependent kinase-like 5 (CDKL5) (NM_003159.2) gene have been associated with early-onset epileptic encephalopathies or Hanefeld variants of RTT(Rett syndrome). In order to clarify the CDKL5 genotype-phenotype correlations in Chinese patients, CDKL5 mutational screening in cases with early-onset epileptic encephalopathies and RTT without MECP2 mutation were performed.

METHODS

The detailed clinical information including clinical manifestation, electroencephalogram (EEG), magnetic resonance imaging (MRI), blood, urine amino acid and organic acid screening of 102 Chinese patients with early-onset epileptic encephalopathies and RTT were collected. CDKL5 gene mutations were analyzed by PCR, direct sequencing and multiplex ligation-dependent probe amplification (MLPA). The patterns of X-chromosome inactivation (XCI) were studied in the female patients with CDKL5 gene mutation.

RESULTS

De novo CDKL5 gene mutations were found in ten patients including one missense mutation (c.533G > A, p.R178Q) which had been reported, two splicing mutations (ISV6 + 1A > G, ISV13 + 1A > G), three micro-deletions (c.1111delC, c.2360delA, c.234delA), two insertions (c.1791 ins G, c.891_892 ins TT in a pair of twins) and one nonsense mutation (c.1375C > T, p.Q459X). Out of ten patients, 7 of 9 females with Hanefeld variants of RTT and the remaining 2 females with early onset epileptic encephalopathy, were detected while only one male with infantile spasms was detected. The common features of all female patients with CDKL5 gene mutations included refractory seizures starting before 4 months of age, severe psychomotor retardation, Rett-like features such as hand stereotypies, deceleration of head growth after birth and poor prognosis. In contrast, the only one male patient with CDKL5 mutation showed no obvious Rett-like features as females in our cohort. The X-chromosome inactivation patterns of all the female patients were random.

CONCLUSIONS

Mutations in CDKL5 gene are responsible for 7 with Hanefeld variants of RTT and 2 with early-onset epileptic encephalopathy in 71 girls as well as for 1 infantile spasms in 31 males. There are some differences in the phenotypes among genders with CDKL5 gene mutations and CDKL5 gene mutation analysis should be considered in both genders.

Structural characterization of the cyclin-dependent protein kinase family

Structural studies of members of the CDK (cyclin-dependent protein kinase) family have made a significant contribution to our understanding of the regulation of protein kinases. The structure of monomeric unphosphorylated CDK2 was the first of an inactive protein kinase to be determined and, since then, structures of other members of the CDK family, alone, in complex with regulatory proteins and in differing phosphorylation states, have enhanced our understanding of the molecular mechanisms regulating protein kinase activity. Recently, our knowledge of the structural biology of the CDK family has been extended by determination of structures for members of the transcriptional CDK and CDK-like kinase branches of the extended family. We include these recent structures in the present review and consider them in the light of current models for CDK activation and regulation.