Cyclin-dependent Kinase-like 5 Mutations Research Articles

Clinical Phenotype of 5 Females With a CDKL5 Mutation

Mutations in the X-linked cyclin dependent kinase like 5 (CDKL5) gene have been reported in approximately 80 patients since the first description in 2003. The clinical presentation partly corresponds with Rett syndrome, considering clinical features as intellectual disability, hypotonia, and poor visual, language, and motor development. However, these patients do not meet the consensus criteria for Rett syndrome since they lack the clear period of regression. Furthermore, in contrast to Rett syndrome, patients with CDKL5 mutations, have seizures or infantile spasms starting in the first weeks of life. We present clinical phenotype of 5 girls having a mutation in the CDKL5 gene. All mutations are novel and are pathogenic since they either lead to a frameshift in the reading frame or affect a consensus splice site. Four of the mutations are detected de novo in the affected girl.

A distinctive seizure type in patients with CDKL5 mutations: Hypermotor-tonic-spasms sequence

Recent recognition of the encephalopathy associated with CDKL5 (cyclin-dependent kinase-like 5) mutations has led to molecular diagnosis in affected girls. A characteristic progressive 3 stage electroclinical epilepsy course occurs with onset by 3 months of age.1,2 After we observed unusual prolonged seizures in a girl with CDKL5 mutations, we sought to determine if CDKL5 mutations were associated with a distinctive electroclinical seizure type. ### Methods. We reviewed the video-EEG monitoring (VEM) and clinical details of all girls with CDKL5 abnormalities recruited into our epilepsy genetics research studies. Details of the molecular methods are described elsewhere.2 In one subject a deletion of CDKL5 was revealed by an Agilent aCGH 44K array and confirmed by quantitative PCR. #### Standard protocol approvals, registrations, and patient consents. The study was approved by the Human Research Ethics Committee of all participating institutions. Signed informed consent for study participation and publication of the videos was obtained from the participants' parents. ### Results. Four of 5 girls with CDKL5 mutations had the distinctive seizure type. The clinical and molecular details are reported (table e-1 on the Neurology ® Web site at www.neurology.org, molecular data previously reported for patients 1, 3, and 43). Table 1 describes the electroclinical features of the seizure type captured during VEM …

CDKL5 gene‐related epileptic encephalopathy: electroclinical findings in the first year of life

Cyclin-dependent kinase-like 5 (CDKL5) gene abnormalities cause an early-onset epileptic encephalopathy. We performed video-electroencephalography (video-EEG) monitoring early in the course of CDKL5-related epileptic encephalopathy in order to examine the early electroclinical characteristics of the condition. We used video-EEG to monitor six infants (five females, one male) with CDKL5-related epileptic encephalopathy (five mutations; one deletion), at ages 45 days to 12 months and followed them up to the ages of 14 months to 5 years (mean age 23 mo). We focused our analysis on the first year of life. The results were evaluated against those of a comparison group of nine infants (aged below 1y) with epileptic encephalography who had tested negative for CDKL5 mutations and deletions. One infant exhibited normal background activity, three exhibited moderate slowing, and two exhibited a suppression burst pattern. Two participants had epileptic spasms and four had a stereotyped complex seizure pattern, which we defined as a 'prolonged' generalized tonic-clonic event consisting of a tonic-tonic/vibratory contraction, followed by a clonic phase with series of spasms, gradually translating into repetitive distal myoclonic jerks. Seizure duration ranged from 2 to 4 minutes. The EEG correlate of each clinical phase included an initial electrodecremental event (tonic vibratory phase), irregular series of sharp waves and spike slow waves (clonic phase with series of spasms), and bilateral rhythmic sharp waves (time locked with myoclonus). Infants with CDKL5-related early epileptic encephalopathy can present in the first year of life with an unusual electroclinical pattern of 'prolonged' generalized tonic-clonic seizures.

CDKL5 gene‐related epileptic encephalopathy: electroclinical findings in the first year of life

Aim Cyclin-dependent kinase-like 5 (CDKL5) gene abnormalities cause an early-onset epileptic encephalopathy. We performed video-electroencephalography (video-EEG) monitoring early in the course of CDKL5-related epileptic encephalopathy in order to examine the early electroclinical characteristics of the condition. Method We used video-EEG to monitor six infants (five females, one male) with CDKL5-related epileptic encephalopathy (five mutations; one deletion), at ages 45 days to 12 months and followed them up to the ages of 14 months to 5 years (mean age 23mo). We focused our analysis on the first year of life. The results were evaluated against those of a comparison group of nine infants (aged below 1y) with epileptic encephalography who had tested negative for CDKL5 mutations and deletions. Results One infant exhibited normal background activity, three exhibited moderate slowing, and two exhibited a suppression burst pattern. Two participants had epileptic spasms and four had a stereotyped complex seizure pattern, which we defined as a ‘prolonged’ generalized tonic–clonic event consisting of a tonic–tonic/vibratory contraction, followed by a clonic phase with series of spasms, gradually translating into repetitive distal myoclonic jerks. Seizure duration ranged from 2 to 4 minutes. The EEG correlate of each clinical phase included an initial electrodecremental event (tonic vibratory phase), irregular series of sharp waves and spike slow waves (clonic phase with series of spasms), and bilateral rhythmic sharp waves (time locked with myoclonus). Interpretation Infants with CDKL5-related early epileptic encephalopathy can present in the first year of life with an unusual electroclinical pattern of ‘prolonged’ generalized tonic–clonic seizures.

Analysis of Hungarian patients with Rett syndrome phenotype for MECP2, CDKL5 and FOXG1 gene mutations

Rett syndrome (RTT) is characterized by a relatively specific clinical phenotype. We screened 152 individuals with RTT phenotype. A total of 22 different known MECP2 mutations were identified in 42 subjects (27.6%). Of the 22 mutations, we identified 7 (31.8%) frameshift-causing deletions, 4 (18.2%) nonsense, 10 (45.5%) missense mutations and one insertion (4.5%). The most frequent pathologic changes were: p.Thr158Met (14.2%) and p.Arg133Cys (11.9%) missense, and p.Arg255Stop (9.5%) and p.Arg294Stop (9.5%) nonsense mutations. We also detected the c.925C >T (p.Arg309Trp) mutation in an affected patient, whose role in RTT pathogenesis is still unknown. Patients without detectable MECP2 defects were screened for mutations of cyclin-dependent kinase-like 5 (CDKL5) gene, responsible for the early-onset variant of RTT. We discovered two novel mutations: c.607G >T resulting in a termination codon at aa203, disrupting the catalytic domain, and c.1708G >T leading to a stop at aa570 of the C terminus. Both patients with CDKL5 mutation presented therapy-resistant epilepsy and a phenotype fitting with the diagnosis of early-onset variant of RTT. No FOXG1 mutation was detected in any of the remaining patients. A total of 110 (72.5%) patients remained without molecular genetic diagnosis that necessitates further search for novel gene mutations in this phenotype. Our results also suggest the need of screening for CDKL5 mutations in patients with Rett phenotype tested negative for MECP2 mutations.

Cyclin-Dependent Kinase-Like 5 (CDKL5) Mutation Screening in Rett Syndrome and Related Disorders

Rett syndrome (RTT) is a severe neurodevelopmental disorder affecting females almost exclusively and is characterized by a wide spectrum of clinical manifestations. Mutations in the X-linked methyl-CpG-binding protein 2 (MECP2) gene have been found in up to 95% of classical RTT cases and a lesser proportion of atypical cases. Recently, mutations in another X-linked gene, CDKL5 (cyclin-dependent kinase-like 5) have been found to cause atypical RTT, in particular the early onset seizure (Hanefeld variant) and one female with autism. In this study we screened several cohorts of children for CDKL5 mutations, totaling 316 patients, including individuals with a clinical diagnosis of RTT but who were negative for MECP2 mutations (n=102), males with X-linked mental retardation (n=9), patients with West syndrome (n=52), patients with autism (n=59), patients with epileptic encephalopathy (n=33), patients with Aicardi syndrome (n=7) and other patients with intellectual disability with or without seizures (n=54). In all, seven polymorphic variations and four de novo mutations (c.586C>T [p.S196L]; c.58G>C [p.G20R]; c.2504delC [p.P835fs]; deletion of exons 1-3) were identified, and in all instances of the latter the clinical phenotype was that of an epileptic encephalopathy. These results suggest that pathogenic CDKL5 mutations are unlikely to be identified in the absence of severe early-onset seizures and highlight the importance of screening for large intragenic and whole gene deletions.

Xp22.3 genomic deletions involving the CDKL5 gene in girls with early onset epileptic encephalopathy

Mutations of the X-linked gene cyclin-dependent kinase-like 5 (CDKL5) cause an X-linked encephalopathy with early onset intractable epilepsy, including infantile spasms and other seizure types, and a Rett syndrome (RTT)-like phenotype. Very limited information is available on the frequency and phenotypic spectrum associated with CDKL5 deletions/duplications. We investigated the role of CDKL5 deletions/duplications in causing early onset intractable epilepsy of unknown etiology in girls. We studied 49 girls with early onset intractable epilepsy, with or without infantile spasms, and developmental impairment, for whom no etiologic factors were obvious after clinical examination, brain magnetic resonance imaging (MRI) and expanded screening for inborn errors of metabolism. We performed CDKL5 gene mutation analysis in all and multiplex ligation dependent probe amplification assay (MLPA) in those who were mutation negative. Custom Array-comparative genomic hybridization (CGH), breakpoint polymerase chain reaction (PCR) analysis, and X-inactivation studies were performed in patients in whom MLPA uncovered a genomic alteration. We found CDKL5 mutations in 8.2% (4 of 49) of patients and genomic deletions in 8.2% (4 of 49). Overall, abnormalities of the CDKL5 gene accounted for 16.3% (8 of 49) of patients. CDKL5 gene deletions are an under-ascertained cause of early onset intractable epilepsy in girls. Genetic testing of CDKL5, including both mutation and deletion/duplication analysis, should be considered in this clinical subgroup.

CDKL5 Expression Is Modulated during Neuronal Development and Its Subcellular Distribution Is Tightly Regulated by the C-terminal Tail

Mutations in the human X-linked cyclin-dependent kinase-like 5 (CDKL5) gene have been identified in patients with Rett syndrome (RTT), West syndrome, and X-linked infantile spasms, sharing the common feature of mental retardation and early seizures. CDKL5 is a rather uncharacterized kinase, but its involvement in RTT seems to be explained by the fact that it works upstream of MeCP2, the main cause of Rett syndrome. To understand the role of this kinase for nervous system functions and to address if molecular mechanisms are involved in regulating its distribution and activity, we studied the ontogeny of CDKL5 expression in developing mouse brains by immunostaining and Western blotting. The expression profile of CDKL5 was compared with that of MeCP2. The two proteins share a general expression profile in the adult mouse brain, but CDKL5 levels appear to be highly modulated at the regional level. Its expression is strongly induced in early postnatal stages, and in the adult brain CDKL5 is present in mature neurons, but not in astroglia. Interestingly, the presence of CDKL5 in the cell nucleus varies at the regional level of the adult brain and is developmentally regulated. CDKL5 shuttles between the cytoplasm and the nucleus and the C-terminal tail is involved in localizing the protein to the cytoplasm in a mechanism depending on active nuclear export. Accordingly, Rett derivatives containing disease-causing truncations of the C terminus are constitutively nuclear, suggesting that they might act as gain of function mutations in this cellular compartment.

Key clinical features to identify girls with CDKL5 mutations

Mutations in the human X-linked cyclin-dependent kinase-like 5 (CDKL5) gene have been shown to cause infantile spasms as well as Rett syndrome (RTT)-like phenotype. To date, less than 25 different mutations have been reported. So far, there are still little data on the key clinical diagnosis criteria and on the natural history of CDKL5-associated encephalopathy. We screened the entire coding region of CDKL5 for mutations in 183 females with encephalopathy with early seizures by denaturing high liquid performance chromatography and direct sequencing, and we identified in 20 unrelated girls, 18 different mutations including 7 novel mutations. These mutations were identified in eight patients with encephalopathy with RTT-like features, five with infantile spasms and seven with encephalopathy with refractory epilepsy. Early epilepsy with normal interictal EEG and severe hypotonia are the key clinical features in identifying patients likely to have CDKL5 mutations. Our study also indicates that these patients clearly exhibit some RTT features such as deceleration of head growth, stereotypies and hand apraxia and that these RTT features become more evident in older and ambulatory patients. However, some RTT signs are clearly absent such as the so called RTT disease profile (period of nearly normal development followed by regression with loss of acquired fine finger skill in early childhood and characteristic intensive eye communication) and the characteristic evolution of the RTT electroencephalogram. Interestingly, in addition to the overall stereotypical symptomatology (age of onset and evolution of the disease) resulting from CDKL5 mutations, atypical forms of CDKL5-related conditions have also been observed. Our data suggest that phenotypic heterogeneity does not correlate with the nature or the position of the mutations or with the pattern of X-chromosome inactivation, but most probably with the functional transcriptional and/or translational consequences of CDKL5 mutations. In conclusion, our report show that search for mutations in CDKL5 is indicated in girls with early onset of a severe intractable seizure disorder or infantile spasms with severe hypotonia, and in girls with RTT-like phenotype and early onset seizures, though, in our cohort, mutations in CDKL5 account for about 10% of the girls affected by these disorders.

The three stages of epilepsy in patients with CDKL5 mutations

Mutations in the X-linked cyclin-dependent kinase-like 5 (CDKL5) gene are responsible for a severe encephalopathy with early epilepsy. So far, the electroclinical phenotype remains largely unknown and no clear genotype-phenotype correlations have been established. To characterize the epilepsy associated with CDKL5 mutations and to look for a relationship between the genotype and the course of epilepsy. We retrospectively analyzed the electroclinical phenotypes of 12 patients aged from 2.5 to 19 years diagnosed with pathogenic CDKL5 mutations and one patient with a novel intronic sequence variation of uncertain pathogenicity and examined whether the severity of the epilepsy was linked to the type and location of mutations. The epilepsy course reveals three successive stages: (Stage I) early epilepsy (onset 1-10 weeks) with normal interictal electroencephalogram (EEG) (10/13) despite frequent convulsive seizures; (Stage II) epileptic encephalopathy with infantile spasms (8/8) and hypsarrhythmia (8/8). At the age of evaluation, seven patients were seizure free and six had developed refractory epilepsy (stage III) with tonic seizures and myoclonia (5/6). Interestingly, the patients carrying a CDKL5 mutations causing a truncation of the catalytic domain tended to develop a more frequent refractory epilepsy than patients with mutations located downstream (4/6, 66.6% versus 1/6, 16%) although, these trends are not yet significant. Our data contribute to a better definition of the epileptic phenotype in CDKL5 mutations, and might give some clues to a potential relationship between the phenotype and the genotype in these patients.

Clinical and electroencephalographic features in patients with CDKL5 mutations: Two new Italian cases and review of the literature

Clinical features and electroencephalographic findings of two patients affected by a previously unreported cyclin-dependent kinase-like 5 (CDKL5) gene mutation are described. Both patients had the Hanefeld variant phenotype with early-onset seizures, but different degrees of clinical severity. In fact, patient 1 was not drug-resistant and is responding to a single drug. On the contrary, patient 2, like most reported cases, has severe epilepsy, exhibits electroencephalographic changes, and is drug resistant. We suggest that the pseudoperiodic patterns observed on the EEGs for these cases represent this genetic form of epilepsy, though differing in frequency, voltage, and associated patterns. This is in agreement with data reported by other authors indicating that no unique pattern can be identified in subjects with CDKL5 mutations. Thus, a CDKL5 investigation should be performed in developmentally delayed patients with early-onset seizures, including drug-resistant subjects with severe EEG changes, as well as in patients with milder, drug-responsive forms of epilepsy.

Impairment of CDKL5 nuclear localisation as a cause for severe infantile encephalopathy

Mutations in the human X-linked cyclin-dependent kinase-like 5 (CDKL5) gene have been shown to cause infantile spasms as well as Rett syndrome-like phenotype. To date, fewer than 20 different mutations...

Seizures and electroencephalographic findings in CDKL5 mutations: Case report and review

Mutations in the X-linked gene cyclin-dependent kinase-like 5 (CDKL5) have been detected in patients presenting with seizures in the first few months of life and Rett syndrome features. Twenty-seven cases have been detected to date. Generalized intractable seizures, as infantile spasms, and generalized tonic–clonic seizures and myoclonic seizures characterize the clinical picture of CDKL5 mutations. Here we report on a patient who presented with sleep-related hyperkinetic seizures. Our observation and review of the literature suggest that a broader polymorphic electroclinical pattern with both generalized and focal seizures may occur in patients with CDKL5 mutations. A screen for CDKL5 mutations is useful in patients, mainly females, with a history of early onset intractable seizures and becomes mandatory when idiopathic infantile spasms and/or atypical Rett syndrome features are also present.

Functional Consequences of Mutations in CDKL5, an X-linked Gene Involved in Infantile Spasms and Mental Retardation

Functional Consequences of Mutations in CDKL5, an X-linked Gene Involved in Infantile Spasms and Mental Retardation