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

Exploring quality of life in individuals with a severe developmental and epileptic encephalopathy, CDKL5 Deficiency Disorder

BACKGROUND

CDKL5 Deficiency Disorder (CDD) is a rare genetic disorder caused by a mutation in the cyclin-dependent kinase-like 5 (CDKL5) gene. It is now considered to be a developmental and epileptic encephalopathy because of the early onset of seizures in association with severe global delay. Other features include cortical visual impairment, sleep and gastro-intestinal problems. Progress in clinical understanding, especially regarding the spectrum of functional ability, seizure patterns, and other comorbidities was initially slow but accelerated in 2012 with the establishment of the International CDKL5 Database (ICDD). Our aim was to use this data source to investigate quality of life (QOL) and associated factors in this disorder.

METHOD

A follow-up questionnaire was administered in 2018 to parents of children registered with the ICDD who had a pathogenic CDKL5 variant. QOL was assessed using QI Disability, an instrument, specifically developed to measure total and specific domains of QOL (physical health, positive emotions, negative emotions, social interaction, leisure and the outdoors (leisure) and independence) in children with intellectual disability. Associations with functional abilities, physical health, mental health and family factors were investigated, initially using univariate analyses followed by multivariate analyses for each of these groups with a final composite model which included the important variables identified from previous models.

RESULTS

Questionnaires were returned by 129/160 families with a child aged >3 years. Functional impairment, including lack of ability to sit, use hands and communicate had the greatest adverse impact on QOL. There were also some relationships with major genotype groupings. Individuals using three or more anti-epileptic medications had poorer QOL than those on one or no medication, particularly in the physical health domain. There was also variation by geographical region with those living in North America typically having the best QOL and those living in middle or lower income countries poorer QOL.

CONCLUSION

Although lower functional abilities were associated with poorer quality of life further research is needed to understand how environmental supports might mitigate this deficit. Comprehensive care and support for both the child and family have important roles to play in helping families to thrive despite the severity of CDD.

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

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

Aged heterozygous Cdkl5 mutant mice exhibit spontaneous epileptic spasms

CDKL5 deficiency disorder (CDD) is a devastating neurodevelopmental disorder characterized by early-onset epilepsy, severe intellectual disability, cortical visual impairment and motor disabilities. Epilepsy is a central feature of CDD, with most patients having intractable seizures, but seizure frequency and severity can vary. Clinical reports demonstrate a diversity in seizure semiology and electrographic features, with no pattern diagnostic of CDD. Although animal models of CDD have shown evidence of hyperexcitability, spontaneous seizures have not been previously reported. Here, we present the first systematic study of spontaneous seizures in mouse models of CDD. Epileptic spasms, the most frequent and persistent seizure type in CDD patients, were recapitulated in two mouse models of CDD carrying heterozygous mutations, Cdkl5^R59X and Cdkl5^KO. Spasm-like events were present in a significant proportion of aged heterozygous female mice carrying either of the two Cdkl5 mutations with significant variability in seizure burden. Electrographically, spasms were most frequently associated with generalized slow-wave activity and tended to occur in clusters during sleep. CDD mice also showed interictal and background abnormalities, characterized by high-amplitude spiking and altered power in multiple frequency bands. These data demonstrate that aged female heterozygous Cdkl5 mice recapitulate multiple features of epilepsy in CDD and can serve to complement existing models of epileptic spasms in future mechanistic and translational studies.

Cyclin-Dependent Kinase-Like 5 (CDKL5): Possible Cellular Signalling Targets and Involvement in CDKL5 Deficiency Disorder

Cyclin-dependent kinase-like 5 (CDKL5, also known as STK9) is a serine/threonine protein kinase originally identified in 1998 during a transcriptional mapping project of the human X chromosome. Thereafter, a mutation in CDKL5 was reported in individuals with the atypical Rett syndrome, a neurodevelopmental disorder, suggesting that CDKL5 plays an important regulatory role in neuronal function. The disease associated with CDKL5 mutation has recently been recognised as CDKL5 deficiency disorder (CDD) and has been distinguished from the Rett syndrome owing to its symptomatic manifestation. Because CDKL5 mutations identified in patients with CDD cause enzymatic loss of function, CDKL5 catalytic activity is likely strongly associated with the disease. Consequently, the exploration of CDKL5 substrate characteristics and regulatory mechanisms of its catalytic activity are important for identifying therapeutic target molecules and developing new treatment. In this review, we summarise recent findings on the phosphorylation of CDKL5 substrates and the mechanisms of CDKL5 phosphorylation and dephosphorylation. We also discuss the relationship between changes in the phosphorylation signalling pathways and the Cdkl5 knockout mouse phenotype and consider future prospects for the treatment of mental and neurological disease associated with CDKL5 mutations.

The Genetic Landscape of Epilepsy of Infancy with Migrating Focal Seizures

OBJECTIVE

Epilepsy of infancy with migrating focal seizures (EIMFS) is one of the most severe developmental and epileptic encephalopathies. We delineate the genetic causes and genotype-phenotype correlations of a large EIMFS cohort.

METHODS

Phenotypic and molecular data were analyzed on patients recruited through an international collaborative study.

RESULTS

We ascertained 135 patients from 128 unrelated families. Ninety-three of 135 (69%) had causative variants (42/55 previously reported) across 23 genes, including 9 novel EIMFS genes: de novo dominant GABRA1, GABRB1, ATP1A3; X-linked CDKL5, PIGA; and recessive ITPA, AIMP1, KARS, WWOX. The most frequently implicated genes were KCNT1 (36/135, 27%) and SCN2A (10/135, 7%). Mosaicism occurred in 2 probands (SCN2A, GABRB3) and 3 unaffected mothers (KCNT1). Median age at seizure onset was 4 weeks, with earlier onset in the SCN2A, KCNQ2, and BRAT1 groups. Epileptic spasms occurred in 22% patients. A total of 127 patients had severe to profound developmental impairment. All but 7 patients had ongoing seizures. Additional features included microcephaly, movement disorders, spasticity, and scoliosis. Mortality occurred in 33% at median age 2 years 7 months.

INTERPRETATION

We identified a genetic cause in 69% of patients with EIMFS. We highlight the genetic heterogeneity of EIMFS with 9 newly implicated genes, bringing the total number to 33. Mosaicism was observed in probands and parents, carrying critical implications for recurrence risk. EIMFS pathophysiology involves diverse molecular processes from gene and protein regulation to ion channel function and solute trafficking. ANN NEUROL 2019;86:821-831.

Gene replacement ameliorates deficits in mouse and human models of cyclin-dependent kinase-like 5 disorder

Cyclin-dependent kinase-like 5 disorder is a severe neurodevelopmental disorder caused by mutations in the X-linked cyclin-dependent kinase-like 5 (CDKL5) gene. It predominantly affects females who typically present with severe early epileptic encephalopathy, global developmental delay, motor dysfunction, autistic features and sleep disturbances. To develop a gene replacement therapy, we initially characterized the human CDKL5 transcript isoforms expressed in the brain, neuroblastoma cell lines, primary astrocytes and embryonic stem cell-derived cortical interneurons. We found that the isoform 1 and to a lesser extent the isoform 2 were expressed in human brain, and both neuronal and glial cell types. These isoforms were subsequently cloned into recombinant adeno-associated viral (AAV) vector genome and high-titre viral vectors were produced. Intrajugular delivery of green fluorescence protein via AAV vector serotype PHP.B in adult wild-type male mice transduced neurons and astrocytes throughout the brain more efficiently than serotype 9. Cdkl5 knockout male mice treated with isoform 1 via intrajugular injection at age 28–30 days exhibited significant behavioural improvements compared to green fluorescence protein-treated controls (1012 vg per animal, n = 10 per group) with PHP.B vectors. Brain expression of the isoform 1 transgene was more abundant in hindbrain than forebrain and midbrain. Transgene brain expression was sporadic at the cellular level and most prominent in hippocampal neurons and cerebellar Purkinje cells. Correction of postsynaptic density protein 95 cerebellar misexpression, a major fine cerebellar structural abnormality in Cdkl5 knockout mice, was found in regions of high transgene expression within the cerebellum. AAV vector serotype DJ efficiently transduced CDKL5-mutant human induced pluripotent stem cell-derived neural progenitors, which were subsequently differentiated into mature neurons. When treating CDKL5-mutant neurons, isoform 1 expression led to an increased density of synaptic puncta, while isoform 2 ameliorated the calcium signalling defect compared to green fluorescence protein control, implying distinct functions of these isoforms in neurons. This study provides the first evidence that gene therapy mediated by AAV vectors can be used for treating CDKL5 disorder.

CDKL5 Deficiency Disorder-A Complex Epileptic Encephalopathy

CDKL5 deficiency disorder (CDD) is a complex of clinical symptoms resulting from the presence of non-functional CDKL5 protein, i.e., serine-threonine kinase (previously referred to as STK9), or its complete absence. The clinical picture is characterized by epileptic seizures (that start within the first three months of life and most often do not respond to pharmacological treatment), epileptic encephalopathy secondary to seizures, and retardation of psychomotor development, which are often observed already in the first months of life. Due to the fact that CDKL5 is located on the X chromosome, the prevalence of CDD among women is four times higher than in men. However, the course is usually more severe among male patients. Recently, many clinical centers have analyzed this condition and provided knowledge on the function of CDKL5 protein, the natural history of the disease, therapeutic options, and their effectiveness and prognosis. The International CDKL5 Disorder Database was established in 2012, which focuses its activity on expanding knowledge related to this condition and disseminating such knowledge to the families of patients.

Seizures in Mouse Models of Rare Neurodevelopmental Disorders

Genetic neurodevelopmental disorders - that often include epilepsy as part of their phenotype - are a heterogeneous and clinically challenging spectrum of disorders in children. Although seizures often contribute significantly to morbidity in these affected populations, the mechanisms of epileptogenesis in these conditions remain poorly understood. Different model systems have been developed to aid in unraveling these mechanisms, which include a number of specific mutant mouse lines which genocopy specific general types of mutations present in patients. These mouse models have not only allowed for assessments of behavioral and electrographic seizure phenotypes to be ascertained, but also have allowed effects on the neurodevelopmental alterations and cognitive impairments associated with these disorders to be examined. In addition, these models play a role in advancing our understanding of these epileptic processes and developing preclinical therapeutics. The concordance of seizure phenotypes - in a select group of rare, genetic, neurodevelopmental disorders and epileptic encephalopathies - found between human patients and their model counterparts will be summarized. This review aims to assess whether models of Rett syndrome, CDKL5 deficiency disorder, Fragile-X syndrome, Dravet syndrome, and Ohtahara syndrome phenocopy the seizures seen in human patients.

Increased DNA Damage and Apoptosis in CDKL5-Deficient Neurons

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

Rodent genetic models of neurodevelopmental disorders and epilepsy

Neurodevelopmental disorders (NDDs) are characterised by cognitive, social and motor deficits and are highly comorbid with intractable epilepsies. Through advances in genetic sequencing technologies a vast number of genes have been implicated in NDDs. State-of-the-art gene-editing techniques have led to the generation of hundreds of mouse models of NDDs. As an example, rodent models of Rett and Dravet syndromes as well as the syndromes caused by mutations in CDKL5 and Syngap1 display cognitive deficits in conjunction with seizure phenotypes. These models allow researchers to understand the underlying mechanisms as well as develop novel treatment strategies that can potentially be translated to the clinic. Furthermore, it may be possible to gain insights into the contribution of epilepsy to the progression of cognitive, social and motor phenotypes in NDDs.

Clinical features of early myoclonic encephalopathy caused by a CDKL5 mutation

BACKGROUND

CDKL5 deficiency is caused by mutations in the cyclin-dependent kinase-like 5 (CDKL5) gene and clinically manifests often in females as drug-resistant intractable epilepsy and severe psychomotor retardation.

CASE REPORT

We report the case of a girl with a CDKL5 mutation born at 39 weeks without neonatal asphyxia. She developed epilepsy at age 1 month with myoclonus of the face and limbs, and non-rhythmic and irregular opsoclonus. She developed tonic seizures and epileptic spasms at 6 months of age and was diagnosed with symptomatic West syndrome and underwent adrenocorticotropic hormone therapy but her seizures were refractory. At the age of 4, she was introduced to our hospital and development was at 2 months of age. We diagnosed her with early myoclonic encephalopathy (EME) due to the remaining suppression-burst pattern observed on an electroencephalogram and her symptoms since onset were mainly myoclonus. At 14 years of age, mutational analysis revealed a CDKL5 mutation (c.380A > G:p.His127Arg). She was diagnosed with epileptic encephalopathy exhibiting clinical features of early myoclonic epilepsy caused by CDKL5 deficiency.

CONCLUSIONS

Early onset epilepsy with severe psychomotor retardation without a known etiology may be caused by a mutation in CDKL5. More research investigating a genotype-phenotype correlation of CDKL5 mutations is necessary because clinical severity may be associated with the location and type of mutations.

Rett Syndrome and CDKL5 Deficiency Disorder: From Bench to Clinic

Rett syndrome (RTT) and CDKL5 deficiency disorder (CDD) are two rare X-linked developmental brain disorders with overlapping but distinct phenotypic features. This review examines the impact of loss of methyl-CpG-binding protein 2 (MeCP2) and cyclin-dependent kinase-like 5 (CDKL5) on clinical phenotype, deficits in synaptic- and circuit-homeostatic mechanisms, seizures, and sleep. In particular, we compare the overlapping and contrasting features between RTT and CDD in clinic and in preclinical studies. Finally, we discuss lessons learned from recent clinical trials while reviewing the findings from pre-clinical studies.

Comparative psychopharmacology of autism and psychotic-affective disorders suggests new targets for treatment

The first treatments showing effectiveness for some psychiatric disorders, such as lithium for bipolar disorder and chlorpromazine for schizophrenia, were discovered by accident. Currently, psychiatric drug design is seen as a scientific enterprise, limited though it remains by the complexity of brain development and function. Relatively few novel and effective drugs have, however, been developed for many years. The purpose of this article is to demonstrate how evolutionary biology can provide a useful framework for psychiatric drug development. The framework is based on a diametrical nature of autism, compared with psychotic-affective disorders (mainly schizophrenia, bipolar disorder and depression). This paradigm follows from two inferences: (i) risks and phenotypes of human psychiatric disorders derive from phenotypes that have evolved along the human lineage and (ii) biological variation is bidirectional (e.g. higher vs lower, faster vs slower, etc.), such that dysregulation of psychological traits varies in two opposite ways. In this context, the author review the evidence salient to the hypothesis that autism and psychotic-affective disorders represent diametrical disorders in terms of current, proposed and potential psychopharmacological treatments. Studies of brain-derived neurotrophic factor, the PI3K pathway, the NMDA receptor, kynurenic acid metabolism, agmatine metabolism, levels of the endocannabinoid anandamide, antidepressants, anticonvulsants, antipsychotics, and other treatments, demonstrate evidence of diametric effects in autism spectrum disorders and phenotypes compared with psychotic-affective disorders and phenotypes. These findings yield insights into treatment mechanisms and the development of new pharmacological therapies, as well as providing an explanation for the longstanding puzzle of antagonism between epilepsy and psychosis. Lay Summary: Consideration of autism and schizophrenia as caused by opposite alterations to brain development and function leads to novel suggestions for pharmacological treatments.

Severity Assessment in CDKL5 Deficiency Disorder

BACKGROUND

Pathologic mutations in cyclin-dependent kinase-like 5 cause CDKL5 deficiency disorder, a genetic syndrome associated with severe epilepsy and cognitive, motor, visual, and autonomic disturbances. This disorder is a relatively common genetic cause of early-life epilepsy. A specific severity assessment is lacking, required to monitor the clinical course and needed to define the natural history and for clinical trial readiness.

METHODS

A severity assessment was developed based on clinical and research experience from the International Foundation for CDKL5 Research Centers of Excellence consortium and the National Institutes of Health Rett and Rett-Related Disorders Natural History Study consortium. An initial draft severity assessment was presented and reviewed at the annual CDKL5 Forum meeting (Boston, 2017). Subsequently it was iterated through four cycles of a modified Delphi process by a group of clinicians, researchers, industry, patient advisory groups, and parents familiar with this disorder until consensus was achieved. The revised version of the severity assessment was presented for review, comment, and piloting to families at the International Foundation for CDKL5 Research-sponsored family meeting (Colorado, 2018). Final revisions were based on this additional input.

RESULTS

The final severity assessment comprised 51 items that comprehensively describe domains of epilepsy; motor; cognition, behavior, vision, and speech; and autonomic functions. Parental ratings of therapy effectiveness and child and family functioning are also included.

CONCLUSIONS

A severity assessment was rapidly developed with input from multiple stakeholders. Refinement through ongoing validation is required for future clinical trials. The consensus methods employed for the development of severity assessment may be applicable to similar rare disorders.

CDKL5 deficiency disorder: Relationship between genotype, epilepsy, cortical visual impairment, and development

OBJECTIVE

The cyclin-dependent kinase like 5 (CDKL5) gene is a known cause of early onset developmental and epileptic encephalopathy, also known as CDKL5 deficiency disorder (CDD). We sought to (1) provide a description of seizure types in patients with CDD, (2) provide an assessment of the frequency of seizure-free periods and cortical visual impairment (CVI), (3) correlate these features with genotype and gender, and (4) correlate these features with developmental milestones.

METHODS

This is a cohort study of patients with CDD. Phenotypic features were explored and correlated with gene variant grouping and gender. A developmental score was created based on achieving seven primary milestones. Phenotypic variables were correlated with the developmental score to explore markers of better developmental outcomes. Multivariate linear regression was used to account for age at last visit.

RESULTS

Ninety-two patients with CDD were seen during the enrollment period. Eighteen were male (19%); median age at last visit was 5 years (interquartile range = 2.0-11.0). Eighty-one percent of patients developed epileptic spasms, but only 47% of those also had hypsarrhythmia. Previously described hypermotor-tonic-spasms sequence was seen in only 24% of patients, but 56% of patients had seizures with multiple phases (often tonic and spasms). Forty-three percent of patients experienced a seizure-free period ranging from 1 to >12 months, but only 6% were still seizure-free at the last visit. CVI was present in 75% of all CDD patients. None of these features was associated with genotype group or gender. CVI was correlated with reduced milestone achievement after adjusting for age at last visit and a history of hypsarrhythmia.

SIGNIFICANCE

The most common seizure types in CDD are epileptic spasms (often without hypsarrhythmia) and tonic seizures that may cluster together. CVI is a common feature in CDD and is correlated with achieving fewer milestones.

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

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

Cannabis for refractory epilepsy in children: A review focusing on CDKL5 Deficiency Disorder

Severe paediatric epilepsies such as CDKL5 Deficiency Disorder (CDD) are extremely debilitating, largely due to the early-onset and refractory nature of the seizures. Existing treatment options are often ineffective and associated with a host of adverse effects, causing those that are affected to seek alternative treatments. Cannabis based products have attracted significant attention over recent years, primarily driven by reports of miraculous cures and a renewed public preference for 'natural' therapies, thus placing intense pressure on health professionals and the government for regulatory change. This study provides a comprehensive overview of the potential role for cannabis in the treatment of CDD. Key areas discussed include the history, mechanism of action, efficacy and safety of cannabis based preparations as well as the burden related to CDD. The evidence supports the use of cannabinoids, especially cannabidiol, in similar forms of refractory epilepsy including Dravet and Lennox-Gastaut syndromes. Evidence for cannabinoids specifically in CDD is limited but growing, with multiple anecdotal reports and an open-label trial showing cannabidiol to be associated with a significant reduction in seizure activity. This review provides the first comprehensive overview of the potential role for cannabis based preparations in the treatment of CDD and provides justification for further clinical and observational research.

Genetics of neonatal-onset epilepsies

Although the majority of seizures in neonates are related to acute brain injury, a substantial minority are the first symptom of a neonatal-onset epilepsy often linked to a pathogenic genetic variant. Historically, studies on neonatal seizures including treatment response and long-term consequences have lumped all etiologies together. However, etiology has been consistently shown to be the most important determinant of outcome. In the past few years, an increasing number of monogenic disorders have been described and might explain up to a third of neonatal-onset epilepsy syndromes previously included under the umbrella of Ohtahara syndrome and early myoclonic encephalopathy. In this chapter, we define the concept of genetic epilepsy and review the classification. Then, we review the most relevant monogenic neonatal-onset epilepsies, detail their underlying pathophysiologic mechanisms, and present their electroclinical phenotypes. We highlight that, in some cases, such as neonates with KCNQ2 or KCNT1 gene mutations, the early recognition of the electroclinical phenotype can lead to targeted diagnostic testing and precision medicine treatment, enabling the possibility of improved outcome.

Impact of biobanks on research outcomes in rare diseases: a systematic review

Background

Alleviating the burden of rare diseases requires research into new diagnostic and therapeutic strategies. We undertook a systematic review to identify and compare the impact of stand-alone registries, registries with biobanks, and rare disease biobanks on research outcomes in rare diseases.

Methods

A systematic review and meta-aggregation was conducted using the preferred reporting items for systematic reviews and meta-analyses (the PRISMA statement). English language publications were sourced from PubMed, Medline, Scopus, and Web of Science. Original research papers that reported clinical, epidemiological, basic or translational research findings derived from data contained in stand-alone registries, registries with biobanks, and rare disease biobanks were considered. Articles selected for inclusion were assessed using the critical appraisal instruments by JBI-QARI. Each article was read in its entirety and findings were extracted using the online data extraction software from JBI-QARI.

Results

Thirty studies including 28 rare disease resources were included in the review. Of those, 14 registries were not associated to biobank infrastructure, 9 registries were associated with biobank infrastructure, and 6 were rare disease biobank resources. Stand-alone registries had the capacity to uncover the natural history of disease and contributed to evidence-based practice. When annexed to biobank infrastructure, registries could also identify and validate biomarkers, uncover novel genes, elucidate pathogenesis at the Omics level, and develop new therapeutic strategies. Rare disease biobanks in this review had similar capacity for biological investigations, but in addition, had far greater sample numbers and higher quality laboratory techniques for quality assurance processes.

Discussion

We examined the research outcomes of three specific populations: stand-alone registries, registries with biobanks, and stand-alone rare disease biobanks and demonstrated that there are key differences among these resources. These differences are a function of the resources’ design, aims, and objectives, with each resource having a distinctive and important role in contributing to the body of knowledge for rare disease research. Whilst stand-alone registries had the capacity to uncover the natural history of disease, develop best practice, replace clinical trials, and improve patient outcomes, they were limited in their capacity to conduct basic research. The role of basic research in rare disease research is vital; scientists must first understand the pathways of disease before they can develop appropriate interventions. Rare disease biobanks, on the other hand (particularly larger biobanks), had the key infrastructure required to conduct basic research, making novel Omics discoveries, identify and validate biomarkers, uncover novel genes, and develop new therapeutic strategies. However, these stand-alone rare disease biobanks did not collect comprehensive data or impact on clinical observations like a rare disease registry.

Rare disease research is important not only for rare diseases, but also for also common diseases. For example, research of low-density lipoprotein (LDL)-receptors in the rare disease known as familial hypercholesterolemia led to the discovery of statins, a drug therapy that is now used routinely to prevent heart disease.

Conclusions

Rare diseases are still under-researched worldwide. This review made the important observation that registries with biobanks had the function of both stand-alone registries (the capacity to collect comprehensive clinical and epidemiological data) and stand-alone rare disease biobanks (the ability to contribute to Omics research). We found registries with biobanks offer a unique, practical, cost-effective, and impactful solution for rare disease research. Linkage of stand-alone registries to rare disease biobanks will provide the appropriate resources required for the effective translation of basic research into clinical practice. Furthermore, facilitators such as collaboration, engagement, blended recruitment, pro-active marketing, broad consent, and “virtual biobank” online catalogues will, if utilised, add to the success of these resources. These important observations can serve to direct future rare diseases research efforts, ultimately improve patient outcomes and alleviate the significant burden associated with rare disease for clinicians, hospitals, society, and most importantly, the patients and their families.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0942-z) contains supplementary material, which is available to authorized users.

Molecular and Synaptic Bases of CDKL5 Disorder

The X-linked gene cyclin-dependent kinase-like 5 (CDKL5) encodes a serine/threonine kinase abundantly expressed in the brain. Mutations in CDKL5 have been associated with neurodevelopmental disorders characterized by early-onset epileptic encephalopathy and severe intellectual disability, suggesting that CDKL5 plays important roles in brain development and function. Recent studies using cultured neurons, knockout mice, and human iPSC-derived neurons have demonstrated that CDKL5 regulates axon outgrowth, dendritic morphogenesis, and synapse formation. The role of CDKL5 in maintaining synaptic function in the mature brain has also begun to emerge. Moreover, mouse models that are deficient for CDKL5 recapitulate some of the key clinical phenotypes in human patients. Here we review these findings related to the function of CDKL5 in the brain and discuss the underlying molecular and cellular mechanisms.

Chemical genetic identification of CDKL5 substrates reveals its role in neuronal microtubule dynamics

Loss‐of‐function mutations in CDKL5 kinase cause severe neurodevelopmental delay and early‐onset seizures. Identification of CDKL5 substrates is key to understanding its function. Using chemical genetics, we found that CDKL5 phosphorylates three microtubule‐associated proteins: MAP1S, EB2 and ARHGEF2, and determined the phosphorylation sites. Substrate phosphorylations are greatly reduced in CDKL5 knockout mice, verifying these as physiological substrates. In CDKL5 knockout mouse neurons, dendritic microtubules have longer EB3‐labelled plus‐end growth duration and these altered dynamics are rescued by reduction of MAP1S levels through shRNA expression, indicating that CDKL5 regulates microtubule dynamics via phosphorylation of MAP1S. We show that phosphorylation by CDKL5 is required for MAP1S dissociation from microtubules. Additionally, anterograde cargo trafficking is compromised in CDKL5 knockout mouse dendrites. Finally, EB2 phosphorylation is reduced in patient‐derived human neurons. Our results reveal a novel activity‐dependent molecular pathway in dendritic microtubule regulation and suggest a pathological mechanism which may contribute to CDKL5 deficiency disorder.

Open-label use of highly purified CBD (Epidiolex®) in patients with CDKL5 deficiency disorder and Aicardi, Dup15q, and Doose syndromes

OBJECTIVE

We studied our collective open-label, compassionate use experience in using cannabidiol (CBD) to treat epilepsy in patients with CDKL5 deficiency disorder and Aicardi, Doose, and Dup15q syndromes.

METHODS

We included patients aged 1-30 years with severe childhood-onset epilepsy who received CBD for ≥10 weeks as part of multiple investigator-initiated expanded access or state access programs for a compassionate prospective interventional study: CDKL5 deficiency disorder (n = 20), Aicardi syndrome (n = 19), Dup15q syndrome (n = 8), and Doose syndrome (n = 8). These patients were treated at 11 institutions from January 2014 to December 2016.

RESULTS

The percent change in median convulsive seizure frequency for all patients taking CBD in the efficacy group decreased from baseline [n = 46] to week 12 (51.4% [n = 35], interquartile range (IQR): 9-85%) and week 48 (59.1% [n = 27], IQR: 14-86%). There was a significant difference between the percent changes in monthly convulsive seizure frequency during baseline and week 12, χ²(2) = 22.9, p = 0.00001, with no difference in seizure percent change between weeks 12 and 48. Of the 55 patients in the safety group, 15 (27%) withdrew from extended observation by week 144: 4 due to adverse effects, 9 due to lack of efficacy, 1 withdrew consent, and 1 was lost to follow-up.

SIGNIFICANCE

This open-label drug trial provides class III evidence for the long-term safety and efficacy of CBD administration in patients with treatment-resistant epilepsy (TRE) associated with CDKL5 deficiency disorder and Aicardi, Dup15q, and Doose syndromes. Adjuvant therapy with CBD showed similar safety and efficacy for these four syndromes as reported in a diverse population of TRE etiologies. This study extended analysis of the prior report from 12 weeks to 48 weeks of efficacy data and suggested that placebo-controlled randomized trials should be conducted to formally assess the safety and efficacy of CBD in these epileptic encephalopathies.

Infantile Epileptic Encephalopathy With Multiple Genetic Mutations: How Important are Variants of Undetermined Significance?

The importance of so called variants of undetermined significance in the development of Infantile Epileptic Encephalopathy is discussed and an illustrative case is presented.

Kinases in synaptic development and neurological diseases

Neuronal morphogenesis and synapse development is essential for building a functioning nervous system, and defects in these processes are associated with neurological disorders. Our understanding of molecular components and signalling events that contribute to neuronal development and pathogenesis is limited. Genes associated with neurodevelopmental and neurodegenerative diseases provide entry points for elucidating molecular events that contribute to these conditions. Several protein kinases, enzymes that regulate protein function by phosphorylating their substrates, are genetically linked to neurological disorders. Identifying substrates of these kinases is key to discovering their function and providing insight for possible therapies. In this review, we describe how various methods for kinase-substrate identification helped elucidate kinase signalling pathways important for neuronal development and function. We describe recent advances on roles of kinases TAOK2, TNIK and CDKL5 in neuronal development and the converging pathways of LRRK2, PINK1 and GAK in Parkinson's Disease.

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.

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.