Neurologic aspects of MECP2 gene duplication in male patients

X-Linked Epilepsies: A Narrative Review

X-linked epilepsies are a heterogeneous group of epileptic conditions, which often overlap with X-linked intellectual disability. To date, various X-linked genes responsible for epilepsy syndromes and/or developmental and epileptic encephalopathies have been recognized. The electro-clinical phenotype is well described for some genes in which epilepsy represents the core symptom, while less phenotypic details have been reported for other recently identified genes. In this review, we comprehensively describe the main features of both X-linked epileptic syndromes thoroughly characterized to date (PCDH19-related DEE, CDKL5-related DEE, MECP2-related disorders), forms of epilepsy related to X-linked neuronal migration disorders (e.g., ARX, DCX, FLNA) and DEEs associated with recently recognized genes (e.g., SLC9A6, SLC35A2, SYN1, ARHGEF9, ATP6AP2, IQSEC2, NEXMIF, PIGA, ALG13, FGF13, GRIA3, SMC1A). It is often difficult to suspect an X-linked mode of transmission in an epilepsy syndrome. Indeed, different models of X-linked inheritance and modifying factors, including epigenetic regulation and X-chromosome inactivation in females, may further complicate genotype-phenotype correlations. The purpose of this work is to provide an extensive and updated narrative review of X-linked epilepsies. This review could support clinicians in the genetic diagnosis and treatment of patients with epilepsy featuring X-linked inheritance.

IRAK1 Duplication in MECP2 Duplication Syndrome Does Not Increase Canonical NF-κB-Induced Inflammation

PURPOSE

Besides their developmental and neurological phenotype, most patients with MECP2/IRAK1 duplication syndrome present with recurrent and severe infections, accompanied by strong inflammation. Respiratory infections are the most common cause of death. Standardized pneumological diagnostics, targeted anti-infectious treatment, and knowledge of the underlying pathomechanism that triggers strong inflammation are unmet clinical needs. We investigated the influence of IRAK1 overexpression on the canonical NF-κB signaling as a possible cause for excessive inflammation in these patients.

METHODS

NF-κB signaling was examined by measuring the production of proinflammatory cytokines and evaluating the IRAK1 phosphorylation and degradation as well as the IκBα degradation upon stimulation with IL-1β and TLR agonists in SV40-immortalized fibroblasts, PBMCs, and whole blood of 9 patients with MECP2/IRAK1 duplication syndrome, respectively.

RESULTS

Both, MECP2/IRAK1-duplicated patients and healthy controls, showed similar production of IL-6 and IL-8 upon activation with IL-1β and TLR2/6 agonists in immortalized fibroblasts. In PBMCs and whole blood, both patients and controls had a similar response of cytokine production after stimulation with IL-1β and TLR4/2/6 agonists. Patients and controls had equivalent patterns of IRAK1 phosphorylation and degradation as well as IκBα degradation upon stimulation with IL-1β.

CONCLUSION

Patients with MECP2/IRAK1 duplication syndrome do not show increased canonical NF-κB signaling in immortalized fibroblasts, PBMCs, and whole blood. Therefore, we assume that these patients do not benefit from a therapeutic suppression of this pathway.

A brief history of MECP2 duplication syndrome: 20-years of clinical understanding

MECP2 duplication syndrome (MDS) is a rare, X-linked, neurodevelopmental disorder caused by a duplication of the methyl-CpG-binding protein 2 (MECP2) gene-a gene in which loss-of-function mutations lead to Rett syndrome (RTT). MDS has an estimated live birth prevalence in males of 1/150,000. The key features of MDS include intellectual disability, developmental delay, hypotonia, seizures, recurrent respiratory infections, gastrointestinal problems, behavioural features of autism and dysmorphic features-although these comorbidities are not yet understood with sufficient granularity. This review has covered the past two decades of MDS case studies and series since the discovery of the disorder in 1999. After comprehensively reviewing the reported characteristics, this review has identified areas of limited knowledge that we recommend may be addressed by better phenotyping this disorder through an international data collection. This endeavour would also serve to delineate the clinical overlap between MDS and RTT.

Electroclinical Features in MECP2 Duplication Syndrome: Pediatric Case Series

OBJECTIVE

MECP2 duplication syndrome (MECP2DS) is an x-linked recessive syndrome characterized by infantile hypotonia, severe neurodevelopmental delay, intellectual disability, progressive spasticity, recurrent infections, and seizures. More than 50% of cases have been associated with epilepsy. Seizure semiology and electroencephalogram (EEG) findings in these patients are poorly described.

METHODS

In this case series, the authors describe the electroclinical features of children with MECP2DS presenting to their institution. In addition, they reviewed seizure types and therapies used.

RESULTS

Eight out of 9 patients with MECP2DS developed epilepsy, with 56% having normal initial EEG. Generalized slowing with generalized and focal/multifocal discharges was the most common EEG pattern which is consistent with prior studies. Atonic seizure was the most common semiology. Majority were pharmacoresistant (63%).

CONCLUSION

The goal of this case series is to better define the clinical and electrophysiological aspects of the epilepsy associated with MECP2 duplication syndrome and provide practical guidance regarding management.

MECP2-Related Disorders in Males

Methyl CpG binding protein 2 (MECP2) is located at Xq28 and is a multifunctional gene with ubiquitous expression. Loss-of-function mutations in MECP2 are associated with Rett syndrome (RTT), which is a well-characterized disorder that affects mainly females. In boys, however, mutations in MECP2 can generate a wide spectrum of clinical presentations that range from mild intellectual impairment to severe neonatal encephalopathy and premature death. Thus, males can be more difficult to classify and diagnose than classical RTT females. In addition, there are some variants of unknown significance in MECP2, which further complicate the diagnosis of these children. Conversely, the entire duplication of the MECP2 gene is related to MECP2 duplication syndrome (MDS). Unlike in RTT, in MDS, males are predominantly affected. Usually, the duplication is inherited from an apparently asymptomatic carrier mother. Both syndromes share some characteristics, but also differ in some aspects regarding the clinical picture and evolution. In the following review, we present a thorough description of the different types of MECP2 variants and alterations that can be found in males, and explore several genotype-phenotype correlations, although there is still a lot to understand.

Visualization and correction of social abnormalities-associated neural ensembles in adult MECP2 duplication mice

Duplications of MECP2-containing genomic segments led to severe autistic symptoms in male. Transgenic mice overexpressing the human MECP2 gene exhibit autistic-like behaviors. Neural circuits underlying social defects in MECP2 transgenic (MECP2-TG) mice remain unknown. To observe neural activity of MECP2-TG mice in vivo, we performed calcium imaging by implantation of microendoscope in the hippocampal CA1 regions of MECP2-TG and wild type (WT) mice. We identified neurons whose activities were tightly associated with social interaction, which activity patterns were compromised in MECP2-TG mice. Strikingly, we rescued the social-related neural activity in CA1 and social defects in MECP2-TG mice by deleting the human MECP2 transgene using the CRISPR/Cas9 method during adulthood. Our data points to the neural circuitry responsible for social interactions and provides potential therapeutic targets for autism in adulthood.

Electroencephalographic and epilepsy findings in mecp2 duplication syndrome. A family study

MECP2 duplication syndrome (MECP2 DS) is an X-linked disorder characterized by early-onset hypotonia, poor speech development, recurrent respiratory infections, epilepsy and progressive spasticity. Epilepsy occurs in more than 50% of the affected patients. Generalized tonic-clonic seizures (GTCS) are the most common seizure-type described but atonic seizures, absences and myoclonic seizures have also been reported. Electroencephalographic (EEG) and seizure types occurring in MECP2 DS have been poorly investigated. Here we report on two male siblings carrying a maternally-inherited MECP2 duplication. Patients underwent several EEG recordings and long-lasting video-EEG monitoring. The most represented seizure types were myoclonic and atonic seizures. GTCS were rarely observed. In patients, we found a slowing of the background activity with multifocal paroxysmal activity, prominent on the frontal areas. In conclusion, our observations seem to suggest that MECP2 syndrome seem to have a peculiar epileptic pattern mainly characterized by the occurrence of myoclonic seizures, the recognition of which is important in order to undertake an appropriate treatment.

Successful corpus callosotomy for post-encephalopathic refractory epilepsy in a patient with MECP2 duplication syndrome

BACKGROUND

Patients with MECP2 duplication syndrome present with distinct facial anomalies and clinical features such as global developmental delay, recurrent respiratory infections, and epileptic seizures. Approximately half of all patients develop epileptic seizures which are refractory in most cases despite active medical management. Furthermore, no previous reports have discussed the efficacy of surgical treatment for seizures in patients with MECP2 duplication syndrome.

CASE REPORT

In the present report, we describe a case of MECP2 duplication syndrome in a 15-year-old boy who developed epileptic seizures following influenza-associated acute encephalitis. His frequent epileptic spasms, tonic, atonic, and partial seizures were refractory to multiple antiepileptic medications. Electroencephalography revealed continuous diffuse epileptic discharge, resulting in regression. A total corpus callosotomy (CC) was performed at the age of 14 years and 7 months. His seizures markedly decreased following CC, although he continued to experience brief partial seizures approximately once per month. Post-operative examination revealed that his epileptic discharges had disappeared, and that his developmental state had returned to pre-encephalopathy levels.

CONCLUSION

Our findings indicate that CC may represent a valuable surgical option for children with medically refractory generalized seizures following acute encephalopathy, irrespective of genetic disorders such as MECP2 duplication syndrome.

Spectrum and time course of epilepsy and the associated cognitive decline in MECP2 duplication syndrome

OBJECTIVE

We characterized the epilepsy features and contribution to cognitive regression in 47 patients with MECP2 duplication syndrome (MDS) and reviewed these characteristics in over 280 MDS published cases.

METHODS

The institutional review board approved this retrospective review of medical records and case histories of patients with MDS.

RESULTS

The average age at enrollment was 10 ± 7 years. Patients with epilepsy were older (13 ± 7 years vs 8 ± 5 years, p = 0.004) and followed for a longer time (11.8 ± 6.5 years vs 6.3 ± 4.2 years, p = 0.003) than patients without a seizure disorder. Epilepsy affected 22/47 (47%) patients with MDS. It was treatment-refractory and consistent with epileptic encephalopathy in 18/22 (82%) cases. Lennox-Gastaut syndrome (LGS) was present in 12/22 (55%) patients and manifested between late childhood and adulthood in 83% of cases. The emergence of neurologic regression coincided with the onset of epilepsy. The MECP2 duplication size and gene content did not correlate with epilepsy presence, type, age at onset, or treatment responsiveness.

CONCLUSION

Epilepsy in MDS is common, often severe, and medically refractory. LGS occurs frequently and may have a late onset. Developmental regression often follows the onset of epilepsy. The MECP2 duplication extent and gene content do not discriminate between patients with or without epilepsy. Our findings inform clinical care and family counseling with respect to early epilepsy recognition, diagnosis, specialty referral, and implementation of aggressive seizure therapy to minimize detrimental effect of uncontrolled seizures on cognitive functions or preexisting neurologic deficits.

Further delineation of the MECP2 duplication syndrome phenotype in 59 French male patients, with a particular focus on morphological and neurological features

The Xq28 duplication involving the MECP2 gene (MECP2 duplication) has been mainly described in male patients with severe developmental delay (DD) associated with spasticity, stereotypic movements and recurrent infections. Nevertheless, only a few series have been published. We aimed to better describe the phenotype of this condition, with a focus on morphological and neurological features. Through a national collaborative study, we report a large French series of 59 affected males with interstitial MECP2 duplication. Most of the patients (93%) shared similar facial features, which evolved with age (midface hypoplasia, narrow and prominent nasal bridge, thick lower lip, large prominent ears), thick hair, livedo of the limbs, tapered fingers, small feet and vasomotor troubles. Early hypotonia and global DD were constant, with 21% of patients unable to walk. In patients able to stand, lower limbs weakness and spasticity led to a singular standing habitus: flexion of the knees, broad-based stance with pseudo-ataxic gait. Scoliosis was frequent (53%), such as divergent strabismus (76%) and hypermetropia (54%), stereotypic movements (89%), without obvious social withdrawal and decreased pain sensitivity (78%). Most of the patients did not develop expressive language, 35% saying few words. Epilepsy was frequent (59%), with a mean onset around 7.4 years of age, and often (62%) drug-resistant. Other medical issues were frequent: constipation (78%), and recurrent infections (89%), mainly lung. We delineate the clinical phenotype of MECP2 duplication syndrome in a large series of 59 males. Pulmonary hypertension appeared as a cause of early death in these patients, advocating its screening early in life.

Expanding the clinical picture of the MECP2 Duplication syndrome

Individuals with two or more copies of the MECP2 gene, located at Xq28, share clinical features and a distinct facial phenotype known as MECP2 Duplication syndrome. We have examined perinatal characteristics, early childhood development and medical co-morbidities in this disorder. The International Rett Syndrome Phenotype Database (InterRett), which collects information from caregivers and clinicians on individuals with Rett syndrome and MECP2 associated disorders, was used as the data source. Data were available on 56 cases (49 males and 7 females) with MECP2 Duplication syndrome. Median age at ascertainment was 7.9 years (range: 1.2-37.6 years) and at diagnosis 3.0 years (range: 3 weeks-37 years). Less than a third (29%) learned to walk. Speech deterioration was reported in 34% and only 20% used word approximations or better at ascertainment. Over half (55%) had been hospitalised for respiratory infections in the first 2 years of life. Just under half (44%) had seizures, occurring daily in nearly half of this group. The majority (89%) had gastrointestinal problems and a third had a gastrostomy. Following the recent demonstration of phenotype reversal in a mouse model of MECP2 Duplication, a clear understanding of the natural history is crucial to the design and implementation of future therapeutic strategies.

Infectious and immunologic phenotype of MECP2 duplication syndrome

MECP2 (methyl CpG binding protein 2) duplication causes syndromic intellectual disability. Patients often suffer from life-threatening infections, suggesting an additional immunodeficiency. We describe for the first time the detailed infectious and immunological phenotype of MECP2 duplication syndrome. 17/27 analyzed patients suffered from pneumonia, 5/27 from at least one episode of sepsis. Encapsulated bacteria (S.pneumoniae, H.influenzae) were frequently isolated. T-cell immunity showed no gross abnormalities in 14/14 patients and IFNy-secretion upon ConA-stimulation was not decreased in 6/7 patients. In 6/21 patients IgG₂-deficiency was detected – in 4/21 patients accompanied by IgA-deficiency, 10/21 patients showed low antibody titers against pneumococci. Supra-normal IgG₁-levels were detected in 11/21 patients and supra-normal IgG₃-levels were seen in 8/21 patients – in 6 of the patients as combined elevation of IgG₁ and IgG₃. Three of the four patients with IgA/IgG₂-deficiency developed multiple severe infections. Upon infections pronounced acute-phase responses were common: 7/10 patients showed CRP values above 200 mg/l. Our data for the first time show systematically that increased susceptibility to infections in MECP2 duplication syndrome is associated with IgA/IgG₂-deficiency, low antibody titers against pneumococci and elevated acute-phase responses. So patients with MECP2 duplication syndrome and low IgA/IgG₂ may benefit from prophylactic substitution of sIgA and IgG.

Late onset epileptic spasms is frequent in MECP2 gene duplication: electroclinical features and long-term follow-up of 8 epilepsy patients

Mutation of the X-linked methyl CpG binding protein 2 (MECP2) has been first identified as the cause of Rett syndrome. More recently, MECP2 gene duplication syndrome has been identified in males. The MECP2 duplication syndrome is characterized by severe mental retardation, infantile hypotonia, progressive spasticity and recurrent infections. Epileptic seizures are inconstant but poorly described. The aim of the study is to describe the electroclinical features of epilepsy in MECP2 duplication patients in order to refine the epilepsy phenotype and its evolution.

METHODS

We conducted a retrospective study in four child neurology departments in France. Eight boys with a MECP2 gene duplication and epilepsy were retrospectively studied. We evaluated both clinical and electroencephalographic data before seizure onset, at seizure onset and during the follow-up.

RESULTS

The patients started seizures at the median age of 6 years (range: 2.5-17 years). Half exhibits late onset epileptic spasms while the other exhibit either focal epilepsy or unclassified generalized epilepsy. Before seizure onset, EEGs were abnormal in all patients showing a slowing of the background or a normal background with fast activities, while EEG performed in epileptic patients, showed a slowing of the background in 6/8 and localized slow or sharp waves in 7/8. Most patients (6/8) have evolved to drug resistant epilepsy.

CONCLUSION

Although late onset epileptic spasms are common in patients with MECP2 duplication, no specific electroclinical phenotype emerges, probably due to genetic heterogeneity of the syndrome. Further studies are needed to individualize specific epileptic subtype in larger cohort of patients.

MECP2 duplication phenotype in symptomatic females: report of three further cases

Background

Xq28 duplications, including MECP2 (methyl CpG-binding protein 2; OMIM 300005), have been identified in approximately 140 male patients presenting with hypotonia, severe developmental delay/intellectual disability, limited or absent speech and ambulation, and recurrent respiratory infections. Female patients with Xq28 duplication have been rarely reported and are usually asymptomatic. Altogether, only fifteen symptomatic females with Xq28 duplications including MECP2 have been reported so far: six of them had interstitial duplications while the remaining had a duplication due to an unbalanced X;autosome translocation. Some of these females present with unspecific mild to moderate intellectual disability whereas a more complex phenotype is reported for females with unbalanced X;autosome translocations.

Findings

Here we report on the clinical features of three other adolescent to adult female patients with Xq28 interstitial duplications of variable size, all including MECP2 gene.

Conclusions

Mild to moderate cognitive impairment together with learning difficulties and speech delay were evident in each of our patients. Moreover, early inadequate behavioral patterns followed by persistent difficulties in the social and communication domains, as well as the occurrence of mild psychiatric disturbances, are common features of these three patients.

MECP2 duplication: possible cause of severe phenotype in females

MECP2 duplication syndrome, originally described in 2005, is an X-linked neurodevelopmental disorder comprising infantile hypotonia, severe to profound intellectual disability, autism or autistic-like features, spasticity, along with a variety of additional features that are not always clinically apparent. The syndrome is due to a duplication (or triplication) of the gene methyl CpG binding protein 2 (MECP2). To date, the disorder has been described almost exclusively in males. Female carriers of the duplication are thought to have no or mild phenotypic features. Recently, a phenotype for females began emerging. We describe a family with ∼290 kb duplication of Xq28 region that includes the MECP2 gene where the proposita and affected family members are female. Twin sisters, presumed identical, presented early with developmental delay, and seizures. Evaluation of the proposita at 25 years of age included microarray comparative genomic hybridization (aCGH) which revealed the MECP2 gene duplication. The same duplication was found in the proposita's sister, who is more severely affected, and the proband's mother who has mild intellectual disability and depression. X-chromosome inactivation studies showed significant skewing in the mother, but was uninformative in the twin sisters. We propose that the MECP2 duplication caused for the phenotype of the proband and her sister. These findings support evidence for varied severity in some females with MECP2 duplications.

MECP2 duplication syndrome in both genders

BACKGROUND

Duplications involving the methyl-CpG-binding protein 2 gene (MECP2) locus at Xq28 have been frequently identified in male patients who exhibit a phenotype unique from that of Rett syndrome, which is mainly characterized by severe mental retardation, recurrent infections, and epilepsy. This combination of features is recognized as MECP2 duplication syndrome.

METHODS

Genomic copy number was investigated for patients with unexplained mental retardation, and phenotypic features of the patients having interstitial duplications including MECP2 were analyzed.

RESULTS

Three male and one female patients with MECP2 duplication were identified. The phenotypic features of all the four patients were compatible with MECP2 duplication syndrome. The X-chromosome inactivation (XCI) pattern was analyzed in the female patient, identifying a skewed XCI that activated the X-chromosome containing the MECP2 duplication. Her mother possessed the same MECP2 duplication and a random XCI pattern but exhibited no phenotypic features, indicating a nonsymptomatic carrier. The brain magnetic resonance imaging revealed periventricular cystic lesions in all four patients, including the female patient.

CONCLUSION

This study suggested clinical implications of the MECP2 duplication syndrome not only in the male but also in female patients with unexplained mental retardation.

Copy number variants in adult patients with Lennox-Gastaut syndrome features

PURPOSE

Lennox-Gastaut syndrome (LGS) is a severe epileptic encephalopathy with complex etiology. To explore possible genetic predispositions and causes of LGS, we have searched for copy number variants (CNVs).

METHODS

We studied 21 patients with LGS or LGS-like epilepsy for CNVs using whole-genome array comparative genomic hybridization (aCGH).

KEY FINDINGS

Eight patients (38%) carried rare CNVs that might contribute to their phenotype. The pathogenicity could be questioned in some of them, but in four patients (19%) a causative role was considered highly probable. Three had CNVs and clinical features consistent with known genetic syndromes: 22q13.3 deletion, 2q23.1 deletion, and MECP2 duplication.

SIGNIFICANCE

There is a high frequency of rare CNVs in adult patients with LGS-like epilepsy. The phenotypes of these background disorders may be obscured by the effects of intractable seizures and massive antiepileptic drug treatment. Previously, syndromic disorders were primarily identified by their clinical features; however, a genome wide approach with identification of the genotype might shed light on the phenotype.

Epilepsy in Rett syndrome, and CDKL5- and FOXG1-gene-related encephalopathies

Rett syndrome is an X-linked neurodevelopmental disorder that manifests in early childhood with developmental stagnation, and loss of spoken language and hand use, with the development of distinctive hand stereotypies, severe cognitive impairment, and autistic features. About 60% of patients have epilepsy. Seizure onset before the age of 3 years is unlikely, and onset after age 20 is rare. Diagnosis of Rett syndrome is based on key clinical elements that identify "typical" Rett syndrome but also "variant" or "atypical" forms. Diagnostic criteria have been modified only slightly over time, even after discovering that MECP2 gene alterations are present in >90% of patients with typical Rett syndrome but only in 50-70% of atypical cases. Over the last several years, intragenic or genomic alterations of the CDKL5 and FOXG1 genes have been associated with severe cognitive impairment, early onset epilepsy and, often, dyskinetic movement disorders, which have variably been defined as Rett variants. It is now clearly emerging that epilepsy has distinctive characteristics in typical Rett syndrome and in the different syndromes caused by CDKL5 and FOXG1 gene alterations. The progressive parting of CDKL5- and FOXG1-gene-related encephalopathies from the core Rett syndrome is reflected by the effort to produce clearer diagnostic criteria for typical and atypical Rett syndrome. Efforts to characterize the molecular pathology underlying these developmental encephalopathies are pointing to abnormalities of telencephalic development, neuronal morphogenesis, maturation and maintenance, and dendritic arborization.

A case report of Chinese brothers with inherited MECP2-containing duplication: autism and intellectual disability, but not seizures or respiratory infections

Background

Autistic spectrum disorders (ASDs) are a family of neurodevelopmental disorders with strong genetic components. Recent studies have shown that copy number variations in dosage sensitive genes can contribute significantly to these disorders. One such gene is the transcription factor MECP2, whose loss of function in females results in Rett syndrome, while its duplication in males results in developmental delay and autism.

Case presentation

Here, we identified a Chinese family with two brothers both inheriting a 2.2 Mb MECP2-containing duplication (151,369,305 – 153,589,577) from their mother. In addition, both brothers also had a 213.7 kb duplication on Chromosome 2, inherited from their father. The older brother also carried a 48.4 kb duplication on Chromosome 2 inherited from the mother, and a 8.2 kb deletion at 11q13.5 inherited from the father. Based on the published literature, MECP2 is the most autism-associated gene among the identified CNVs. Consistently, the boys displayed clinical features in common with other patients carrying MECP2 duplications, including intellectual disability, autism, lack of speech, slight hypotonia and unsteadiness of movement. They also had slight dysmorphic features including a depressed nose bridge, large ears and midface hypoplasia. Interestingly, they did not exhibit other clinical features commonly observed in American-European patients with MECP2 duplication, including recurrent respiratory infections and epilepsy.

Conclusions

To our knowledge, this is the first identification and characterization of Chinese Han patients with MECP2-containing duplications. Further cases are required to determine if the above described clinical differences are due to individual variations or related to the genetic background of the patients.

A partial MECP2 duplication in a mildly affected adult male: a putative role for the 3' untranslated region in the MECP2 duplication phenotype

Background

Duplications of the X-linked MECP2 gene are associated with moderate to severe intellectual disability, epilepsy, and neuropsychiatric illness in males, while triplications are associated with a more severe phenotype. Most carrier females show complete skewing of X-inactivation in peripheral blood and an apparent susceptibility to specific personality traits or neuropsychiatric symptoms.

Methods

We describe the clinical phenotype of a pedigree segregating a duplication of MECP2 found on clinical array comparative genomic hybridization. The position, size, and extent of the duplication were delineated in peripheral blood samples from affected individuals using multiplex ligation-dependent probe amplification and fluorescence in situ hybridization, as well as targeted high-resolution oligonucleotide microarray analysis and long-range PCR. The molecular consequences of the rearrangement were studied in lymphoblast cell lines using quantitative real-time PCR, reverse transcriptase PCR, and western blot analysis.

Results

We observed a partial MECP2 duplication in an adult male with epilepsy and mild neurocognitive impairment who was able to function independently; this phenotype has not previously been reported among males harboring gains in MECP2 copy number. The same duplication was inherited by this individual’s daughter who was also affected with neurocognitive impairment and epilepsy and carried an additional copy-number variant. The duplicated segment involved all four exons of MECP2, but excluded almost the entire 3' untranslated region (UTR), and the genomic rearrangement resulted in a MECP2-TEX28 fusion gene mRNA transcript. Increased expression of MECP2 and the resulting fusion gene were both confirmed; however, western blot analysis of lysates from lymphoblast cells demonstrated increased MeCP2 protein without evidence of a stable fusion gene protein product.

Conclusion

The observations of a mildly affected adult male with a MECP2 duplication and paternal transmission of this duplication are unique among reported cases with a duplication of MECP2. The clinical and molecular findings imply a minimal critical region for the full neurocognitive expression of the MECP2 duplication syndrome, and suggest a role for the 3′ UTR in mitigating the severity of the disease phenotype.

Electroclinical pattern in MECP2 duplication syndrome: eight new reported cases and review of literature

PURPOSE

Duplications encompassing the MECP2 gene on the Xq28 region have been described in male patients with moderate to severe mental retardation, absent speech, neonatal hypotonia, progressive spasticity and/or ataxia, recurrent severe respiratory infections, gastrointestinal problems, mild facial dysmorphisms (midface hypoplasia, depressed nasal bridge, large ears) and epilepsy. Epilepsy can occur in >50% of cases, but the types of seizures and the electroclinical findings in affected male individuals have been poorly investigated up to the present. Herein we describe eight patients with MECP2 duplication syndrome and a specific clinical and electroencephalographic pattern.

METHODS

Array CGH of genomic DNA from the probands was performed, and an Xq28 duplication ranging from 209 kb to 6.36 Mb was found in each patient. Electroencephalography studies and clinical and seizure features of all the patients were analyzed.

KEY FINDINGS

We found that epilepsy tended to occur between late childhood and adolescence. Episodes of loss of tone of the head and/or the trunk were the most represented seizure types. Generalized tonic-clonic seizures were rarely observed. The typical interictal EEG pattern showed abnormal background activity, with generalized slow spike and wave asynchronous discharge with frontotemporal predominance. Sleep electroencephalography studies also demonstrated abnormal background activity; spindles and K complex were often abnormal in morphology and amplitude. Response to therapy was generally poor and drug resistance was a significant feature.

SIGNIFICANCE

Although these cases and a review of the literature indicate that epilepsy associated with MECP2 duplication syndrome cannot be considered a useful marker for early diagnosis, epilepsy is present in >90% of adolescent patients and shows a peculiar electroclinical pattern. Consequently, it should be considered a significant sign of the syndrome, and an EEG follow-up of these patients should be encouraged from early childhood. Moreover, the definition of a more specific epileptic phenotype could be useful in order to suspect MECP2 duplication syndrome in older undiagnosed patients.

Xq28 duplications including MECP2 in five females: Expanding the phenotype to severe mental retardation

Duplications leading to functional disomy of chromosome Xq28, including MECP2 as the critical dosage-sensitive gene, are associated with a distinct clinical phenotype in males, characterized by severe mental retardation, infantile hypotonia, progressive neurologic impairment, recurrent infections, bladder dysfunction, and absent speech.

Female patients with Xq duplications including MECP2 are rare. Only recently submicroscopic duplications of this region on Xq28 have been recognized in four females, and a triplication in a fifth, all in combination with random X-chromosome inactivation (XCI). Based on this small series, it was concluded that in females with MECP2 duplication and random XCI, the typical symptoms of affected boys are not present. We present clinical and molecular data on a series of five females with an Xq28 duplication including the MECP2 gene, both isolated and as the result of a translocation, and compare them with the previously reported cases of small duplications in females. The collected data indicate that the associated phenotype in females is distinct from males with similar duplications, but the clinical effects may be as severe as seen in males.

MECP2 Duplication Syndrome

Since the initial report that clearly established a causal role between duplication of the MECP2 gene and a severe syndromic form of intellectual disability, many new patients have been identified and reported, and the etiology in already published families solved. This has led to the establishment of a clinically recognizable disorder. Here, we review the clinical data of 129 reported and nonreported male patients with MECP2 duplication syndrome.

Analysis of MECP2 gene copy number in boys with autism

Autism is a severe neurodevelopmental disorder with a strong genetic basis.The methyl-CpG binding protein 2 gene (MECP2) is a dosage-sensitive gene in brain development and has been implicated as a candidate gene for autism. Duplication of the MECP2 gene has been reported in a few boys with autistic features. To further investigate the association of MECP2 duplication with autism, the authors performed real-time quantitative polymerase chain reaction (PCR) to detect copy number variations of the MECP2 gene in 82 autistic boys. No copy number variation was found in these patients, indicating that duplication of the MECP2 gene is not frequent in autistic patients. The authors consider that duplication of the MECP2 gene has no major effect on the susceptibility to autism. Replication of studies in a large-sized sample and a well-characterized subgroup of autism are warranted to further identify the association of MECP2 gene duplication with autism.

Epigenetics, copy number variation, and other molecular mechanisms underlying neurodevelopmental disabilities: new insights and diagnostic approaches

The diagnostic evaluation of children with intellectual disability (ID) and other neurodevelopmental disabilities (NDD) has become increasingly complex in recent years owing to a number of newly recognized genetic mechanisms and sophisticated methods to diagnose them. Previous studies have attempted to address the diagnostic yield of finding a genetic cause in ID. The results have varied widely from 10% to 81%, with the highest percentage being found in studies using new array comparative genomic hybridization methodology especially in autism. Although many cases of ID/NDD result from chromosomal aneuploidy or structural rearrangements, single gene disorders and new categories of genome modification, including epigenetics and copy number variation play an increasingly important role in diagnosis and testing. Epigenetic mechanisms, such as DNA methylation and modifications to histone proteins, regulate high-order DNA structure and gene expression. Aberrant epigenetic and copy number variation mechanisms are involved in several neurodevelopmental and neurodegenerative disorders including Rett syndrome, fragile X syndrome, and microdeletion syndromes. This review will describe a number of the molecular genetic mechanisms that play a role in disorders leading to ID/NDD and will discuss the categories and technologies for diagnostic testing of these conditions.

The MECP2 duplication syndrome

In this review, we detail the history, molecular diagnosis, epidemiology, and clinical features of the MECP2 duplication syndrome, including considerations for the care of patients with this X-linked neurodevelopmental disorder. MECP2 duplication syndrome is 100% penetrant in affected males and is associated with infantile hypotonia, severe to profound mental retardation, autism or autistic features, poor speech development, recurrent infections, epilepsy, progressive spasticity, and, in some cases, developmental regression. Most of the reported cases are inherited, however, de novo cases have been documented. While carrier females have been reported to be unaffected, more recent research demonstrates that despite normal intelligence, female carriers display a range of neuropsychiatric phenotypes that pre-date the birth of an affected son. Given what we know of the syndrome to date, we propose that genetic testing is warranted in cases of males with infantile hypotonia and in cases of boys with mental retardation and autistic features with or without recurrent infections, progressive spasticity, epilepsy, or developmental regression. We discuss recommendations for clinical management and surveillance as well as the need for further clinical, genotype-phenotype, and molecular studies to assist the patients and their families who are affected by this syndrome.

Progressive cerebellar degenerative changes in the severe mental retardation syndrome caused by duplication of MECP2 and adjacent loci on Xq28

Localised duplications, involving the MECP2 locus, at Xq28 have been associated with a syndrome comprising X-linked mental retardation, hypotonia and recurrent infections in males. We now present neuroradiological evidence that progressive cerebellar degenerative changes may also be a consistent feature of this syndrome, emerging in the second decade of life. We report seven affected males, from three different families who, in addition to the previously described clinical findings, have a reduction in the volume of the white matter and mild dilatation of the lateral ventricles. Three of the older patients show a consistent cerebellar degenerative phenotype. Furthermore, we describe the first female affected with the disorder. The female was mildly affected and shows X-inactivation in the ratio of 70:30, demonstrating that X-inactivation cannot be exclusively relied upon to spare the female carriers from symptoms. In conclusion, there is a radiological phenotype associated with Xq28 duplication which clearly demonstrates progressive degenerative cerebellar disease as part of the syndrome.

Elevated expression of MeCP2 in cardiac and skeletal tissues is detrimental for normal development

MeCP2 plays a critical role in interpreting epigenetic signatures that command chromatin conformation and regulation of gene transcription. In spite of MeCP2's ubiquitous expression, its functions have always been considered in the context of brain physiology. In this study, we demonstrate that alterations of the normal pattern of expression of MeCP2 in cardiac and skeletal tissues are detrimental for normal development. Overexpression of MeCP2 in the mouse heart leads to embryonic lethality with cardiac septum hypertrophy and dysregulated expression of MeCP2 in skeletal tissue produces severe malformations. We further show that MeCP2's expression in the heart is developmentally regulated; further suggesting that it plays a key role in regulating transcriptional programs in non-neural tissues.