MeCP2 mutations in children with and without the phenotype of Rett syndrome

Genetic Instability and Disease Progression of Indian Rett Syndrome Patients

Rett syndrome (RTT) is the rare neurodevelopmental disorder caused by mutations in methyl CpG binding protein 2 (MECP2) gene with a prevalence of 1:10,000 worldwide. The hallmark clinical features of RTT are developmental delay, microcephaly, repetitive behaviours, gait abnormalities, respiratory abnormalities and seizures. Still, the understanding on the diagnosis of RTT among clinicians are less. The aim of our work was to study various clinical manifestations and a spectrum of MECP2 genetic heterogeneity in RTT patients from South Indian population. We screened 208 autistic patients and diagnosed 20 RTT patients, who were further divided into classical RTT (group I; N = 11) and variant RTT (group II; N = 9). The clinical severity of RTT was measured using RSSS, RSBQ, SSI, SSS and RTT gross motor scale. The biochemical analysis showed that thyroid-stimulating hormone (TSH), plasma dopamine and cholesterol levels were higher in group I when compared to group II, whereas the level of blood pressure, calcium, ferritin and high-density lipoprotein levels were significantly decreased in both RTT groups, when compared to the control group. The genetic mutational spectrum of MECP2 mutations were found in 12/20 of RTT patients, which revealed the occurrence of 60% pathogenic mutation and 20% unknown mutation and it was correlated with the clinical finding of respiratory dysfunction, scoliosis and sleeping problems. The significant results of this study provided clinical and genetic aspects of RTT diagnosis and proposed the clinicians to screen abnormal cholesterol, calcium and TSH levels tailed with MECP2 gene mutations for early prognosis of disease severity.

A female patient with adolescent-onset progressive myoclonus epilepsy carrying a truncating MECP2 mutation

BACKGROUND

MECP2 is a well-known causative gene for Rett syndrome but other phenotypes have also been reported. Here, we report a case of a female patient with adolescent-onset progressive myoclonus epilepsy (PME) carrying a novel truncating mutation in the MECP2 gene.

CASE REPORT

The patient was a 29-year-old woman with infantile-onset intellectual disability of unspecified cause. She had demonstrated slow but steady development with moderate intellectual disability until the age of 16, when she started having epileptic seizures. Her epilepsy progressed intractably with multiple seizure types accompanied by myoclonus, tremor, and gradual regression. She is currently apathetic and requires extensive assistance in all aspects of life. After an extensive work-up for underlying diseases for PME turned out negative, whole-exome sequencing revealed a de novo 113-bp deletion and 3-bp insertion in MECP2, a variant of NM_004992.4:c.1099_1211delinsGGG, p.(His367Glyfs*32).

CONCLUSIONS

The clinical presentation of this case was inconsistent with Rett syndrome, and the rapid regression in the patient's twenties was considered characteristic. Mutations of MECP2 may result in variable neurodevelopmental phenotypes and may also be considered a causative gene for adolescent-onset PME.

Brain structural alterations in young girls with Rett syndrome: A voxel-based morphometry and tract-based spatial statistics study

Rett syndrome (RTT) is a neurodevelopmental disorder caused by loss-of-function variants in the MECP2 gene, currently with no cure. Neuroimaging is an important tool for obtaining non-invasive structural and functional information about the in vivo brain. Multiple approaches to magnetic resonance imaging (MRI) scans have been utilized effectively in RTT patients to understand the possible pathological basis. This study combined developmental evaluations with clinical severity, T1-weighted imaging, and diffusion tensor imaging, aiming to explore the structural alterations in cohorts of young girls with RTT, idiopathic autism spectrum disorder (ASD), or typical development. Voxel-based morphometry (VBM) was used to determine the voxel-wised volumetric characteristics of gray matter, while tract-based spatial statistics (SPSS) was used to obtain voxel-wised properties of white matter. Finally, a correlation analysis between the brain structural alterations and the clinical evaluations was performed. In the RTT group, VBM revealed decreased gray matter volume in the insula, frontal cortex, calcarine, and limbic/paralimbic regions; TBSS demonstrated decreased fractional anisotropy (FA) and increased mean diffusivity (MD) mainly in the corpus callosum and other projection and association fibers such as superior longitudinal fasciculus and corona radiata. The social impairment quotient and clinical severity were associated with these morphometric alterations. This monogenic study with an early stage of RTT may provide some valuable guidance for understanding the disease pathogenesis. At the same time, the pediatric-adjusted analytic pipelines for VBM and TBSS were introduced for significant improvement over classical approaches for MRI scans in children.

A transcranial magnetic stimulation study for the characterization of corticospinal pathway plasticity in children with neurological disorders

We aimed to investigate cortical and radicular TMS-evoked motor evoked potentials (MEPs) in children with neurological disorders (n = 57, mean age: 5.45 years) and agematched healthy controls (n = 46). Four TMS parameters were analyzed: MEP amplitudes, the latencies of MEP, the latency jump (cortical MEP latency at rest - cortical active-MEP latency at with slightly contracted targeted muscle), and central motor conduction time. Children with neurological disorders were categorized according to the two major types of neuronal plasticity; excessive plasticity: 29 children with cerebral palsy and impaired plasticity: 28 children with neurodegenerative diseases, stroke, and central nervous system infections. The active-MEP abnormalities (absent and prolonged latencies) were correlated with the location of cortical involvement on MRI patterns. We obtained a significantly increased rate of abnormal cortical active-MEPs in children with impaired plasticity (21/28, 75%) compared with excessive plasticity (18/29, 62%). The rate of absent MEP response is three times more in children with impaired plasticity (43%) than in children with excessive plasticity (14%). A more reduced latency jump was measured in children with impaired plasticity compared to children with excessive plasticity. TMS-evoked active-MEPs and latency jumping are valuable parameters for characterizing neuronal plasticity in children with neurological disorders.

RNA Modifications and RNA Metabolism in Neurological Disease Pathogenesis

The intrinsic cellular heterogeneity and molecular complexity of the mammalian nervous system relies substantially on the dynamic nature and spatiotemporal patterning of gene expression. These features of gene expression are achieved in part through mechanisms involving various epigenetic processes such as DNA methylation, post-translational histone modifications, and non-coding RNA activity, amongst others. In concert, another regulatory layer by which RNA bases and sugar residues are chemically modified enhances neuronal transcriptome complexity. Similar RNA modifications in other systems collectively constitute the cellular epitranscriptome that integrates and impacts various physiological processes. The epitranscriptome is dynamic and is reshaped constantly to regulate vital processes such as development, differentiation and stress responses. Perturbations of the epitranscriptome can lead to various pathogenic conditions, including cancer, cardiovascular abnormalities and neurological diseases. Recent advances in next-generation sequencing technologies have enabled us to identify and locate modified bases/sugars on different RNA species. These RNA modifications modulate the stability, transport and, most importantly, translation of RNA. In this review, we discuss the formation and functions of some frequently observed RNA modifications—including methylations of adenine and cytosine bases, and isomerization of uridine to pseudouridine—at various layers of RNA metabolism, together with their contributions to abnormal physiological conditions that can lead to various neurodevelopmental and neurological disorders.

MECP2-related conditions in males: A systematic literature review and 8 additional cases

OBJECTIVE

To present a cohort of 8 males and perform a systematic review of all published cases with a single copy of MECP2 carrying a pathogenic variant.

METHODS

We reviewed medical records of males with a single copy of MECP2 carrying a pathogenic variant. We searched in Medline (Pubmed) and Embase to collect all articles which included well-characterized males with a single copy of MECP2 carrying a pathogenic or likely pathogenic variant in MECP2 (1999-2020).

RESULTS

The literature search yielded a total of 3,185 publications, of which 58 were included in our systematic review. We were able to collect information on 27 published patients with severe neonatal encephalopathy, 47 individuals with isolated or familial mental retardation X-linked 13 (XLMR13), as well as 24 individuals with isolated or familial Pyramidal signs, parkinsonism, and macroorchidism (PPM-X). In our cohort, we met eight individuals aged 4 to 19-year-old at the last evaluation. Three MECP2-associated phenotypes were seen in male carriers of a single copy of the gene: severe neonatal encephalopathy (n = 5); X-linked intellectual deficiency 13 (n = 2); and pyramidal signs, parkinsonism, and macroorchidism (PPM-X) (n = 1). Two novel de novo variants [p.(Gly252Argfs∗7) and p.(Tyr132Cys)] were detected.

CONCLUSION

In males, the MECP2 pathogenic variants can be associated with different phenotypes, including neonatal severe encephalopathy, intellectual deficiency, or late-onset parkinsonism and spasticity. The typical RS phenotype is not expected in males, except in those with Klinefelter syndrome or somatic mosaicism for MECP2.

Sub-genic intolerance, ClinVar, and the epilepsies: A whole-exome sequencing study of 29,165 individuals

Both mild and severe epilepsies are influenced by variants in the same genes, yet an explanation for the resulting phenotypic variation is unknown. As part of the ongoing Epi25 Collaboration, we performed a whole-exome sequencing analysis of 13,487 epilepsy-affected individuals and 15,678 control individuals. While prior Epi25 studies focused on gene-based collapsing analyses, we asked how the pattern of variation within genes differs by epilepsy type. Specifically, we compared the genetic architectures of severe developmental and epileptic encephalopathies (DEEs) and two generally less severe epilepsies, genetic generalized epilepsy and non-acquired focal epilepsy (NAFE). Our gene-based rare variant collapsing analysis used geographic ancestry-based clustering that included broader ancestries than previously possible and revealed novel associations. Using the missense intolerance ratio (MTR), we found that variants in DEE-affected individuals are in significantly more intolerant genic sub-regions than those in NAFE-affected individuals. Only previously reported pathogenic variants absent in available genomic datasets showed a significant burden in epilepsy-affected individuals compared with control individuals, and the ultra-rare pathogenic variants associated with DEE were located in more intolerant genic sub-regions than variants associated with non-DEE epilepsies. MTR filtering improved the yield of ultra-rare pathogenic variants in affected individuals compared with control individuals. Finally, analysis of variants in genes without a disease association revealed a significant burden of loss-of-function variants in the genes most intolerant to such variation, indicating additional epilepsy-risk genes yet to be discovered. Taken together, our study suggests that genic and sub-genic intolerance are critical characteristics for interpreting the effects of variation in genes that influence epilepsy.

Experiences with offering pro bono medical genetics services in the West Indies: Benefits to patients, physicians, and the community

We describe our experiences with organizing pro bono medical genetics and neurology outreach programs on several different resource-limited islands in the West Indies. Due to geographic isolation, small population sizes, and socioeconomic disparities, most Caribbean islands lack medical services for managing, diagnosing, and counseling individuals with genetic disorders. From 2015 to 2019, we organized 2-3 clinics per year on various islands in the Caribbean. We also organized a week-long clinic to provide evaluations for children suspected of having autism spectrum disorder. Consultations for over 100 different individuals with suspected genetic disorders were performed in clinics or during home visits following referral by locally registered physicians. When possible, follow-up visits were attempted. When available and appropriate, clinical samples were shipped to collaborating laboratories for molecular analysis. Laboratory tests included karyotyping, cytogenomic microarray analysis, exome sequencing, triplet repeat expansion testing, blood amino acid level determination, biochemical assaying, and metabolomic profiling. We believe that significant contributions to healthcare by genetics professionals can be made even if availability is limited. Visiting geneticists may help by providing continuing medical education seminars. Clinical teaching rounds help to inform local physicians regarding the management of genetic disorders with the aim of generating awareness of genetic conditions. Even when only periodically available, a visiting geneticist may benefit affected individuals, their families, their local physicians, and the community at large.

De novo loss-of-function variants in X-linked MED12 are associated with Hardikar syndrome in females

PURPOSE

Hardikar syndrome (MIM 612726) is a rare multiple congenital anomaly syndrome characterized by facial clefting, pigmentary retinopathy, biliary anomalies, and intestinal malrotation, but with preserved cognition. Only four patients have been reported previously, and none had a molecular diagnosis. Our objective was to identify the genetic basis of Hardikar syndrome (HS) and expand the phenotypic spectrum of this disorder.

METHODS

We performed exome sequencing on two previously reported and five unpublished female patients with a clinical diagnosis of HS. X-chromosome inactivation (XCI) studies were also performed.

RESULTS

We report clinical features of HS with previously undescribed phenotypes, including a fatal unprovoked intracranial hemorrhage at age 21. We additionally report the discovery of de novo pathogenic nonsense and frameshift variants in MED12 in these seven individuals and evidence of extremely skewed XCI in all patients with informative testing.

CONCLUSION

Pathogenic missense variants in the X-chromosome gene MED12 have previously been associated with Opitz-Kaveggia syndrome, Lujan syndrome, Ohdo syndrome, and nonsyndromic intellectual disability, primarily in males. We propose a fifth, female-specific phenotype for MED12, and suggest that nonsense and frameshift loss-of-function MED12 variants in females cause HS. This expands the MED12-associated phenotype in females beyond intellectual disability.

Sleep disordered breathing and daytime hypoventilation in a male with MECP2 mutation

Rett syndrome (RTT, MIM * 312750) is an X-linked neurodevelopmental disorder caused by pathogenic variants at the Xq28 region involving the gene methyl-CpG-binding protein 2 (MECP2, MIM * 300005). The spectrum of MECP2-related phenotypes is wide and it ranges from asymptomatic female carriers to severe neonatal-onset encephalopathy in males. Abnormal breathing represents one of the leading features, but today little is known about polysomnographic features in RTT females; no data are available about males. We report the case of a male of Moroccan origins with a MECP2 pathogenic variant and a history of encephalopathy and severe breathing disturbances in the absence of dysmorphic features. For the first time we describe in detail the polysomnographic characteristics of a MECP2-mutated male and we show the relevance of severe central apneas, which may represent a new clinical clue to suggest the diagnosis. Moreover, we want to highlight the importance to maintain a high index of suspicion for MECP2-related disorders in the presence of severe hypotonia, apneic crises, and respiratory insufficiency in males to permit an earlier diagnosis and the consequent definition of recurrence risk of the family and to avoid other useless and invasive exams.

MECP2 mutation spectrum and its clinical characteristics in a Chinese cohort

The dysfunction of methyl-CpG-binding protein 2 (MeCP2) is associated with several neurological disorders, of which Rett syndrome (RTT) is the most prominent. This study focused on a Chinese patient cohort with MECP2 mutations, and analyzed the characteristics of these mutations and their clinical manifestations. In total, 666 patients were identified with 126 different MECP2 mutations, including 22 novel mutations. Over 80% of patients carried an MECP2 mutation on exon 4. Nonsense and missense mutations were the most commonly reported types. Missense mutations were mainly located on methyl-CpG-binding domain (MBD), and nonsense mutations predominantly occurred on transcription repression domain (TRD) and inter domain. The predilection site of large deletion was exon 3 and/or exon 4. Patients with p.R133C, p.R294*, p.R306C, and C-terminal domain (CTD) deletions were less severely affected. Significant differences were found in ambulation ability, hand function, and language among different mutation groups. Three female patients with MECP2 mutations (1 with p.R306P and 2 with p.R309W) only presented with intellectual disability/developmental delay (ID/DD), and no obvious RTT symptoms were reported. Eight male individuals with MECP2 mutations were also identified in this study, including 2 diagnosed with typical RTT, 3 with atypical RTT and 3 with ID/DD.

Diurnal variation in autonomic regulation among patients with genotyped Rett syndrome

BACKGROUND

Rett syndrome is a severe neurological disorder with a range of disabling autonomic and respiratory symptoms and resulting predominantly from variants in the methyl-CpG binding protein 2 gene on the long arm of the X-chromosome. As basic research begins to suggest potential treatments, sensitive measures of the dynamic phenotype are needed to evaluate the results of these research efforts. Here we test the hypothesis that the physiological fingerprint of Rett syndrome in a naturalistic environment differs from that of controls, and differs among genotypes within Rett syndrome.

METHODS

A comprehensive array of heart rate variability, cardiorespiratory coupling and cardiac repolarisation measures were evaluated from an existing database of overnight and daytime inhome ambulatory recordings in 47 cases and matched controls.

RESULTS

Differences between girls with Rett syndrome and matched controls were apparent in a range of autonomic measures, and suggest a shift towards sympathetic activation and/or parasympathetic inactivation. Daily temporal trends analysed in the context of circadian rhythms reveal alterations in amplitude and phase of diurnal patterns of autonomic balance. Further analysis by genotype class confirms a graded presentation of the Rett syndrome phenotype such that patients with early truncating mutations were most different from controls, while late truncating and missense mutations were least different from controls.

CONCLUSIONS

Comprehensive autonomic measures from extensive inhome physiological measurements can detect subtle variations in the phenotype of girls with Rett syndrome, suggesting these techniques are suitable for guiding novel therapies.

Rett Syndrome, a Neurodevelopmental Disorder, Whole-Transcriptome, and Mitochondrial Genome Multiomics Analyses Identify Novel Variations and Disease Pathways

Rett syndrome (RTT) is a severe neurodevelopmental disorder reported worldwide in diverse populations. RTT is diagnosed primarily in females, with clinical findings manifesting early in life. Despite the variable rates across populations, RTT has an estimated prevalence of ∼1 in 10,000 live female births. Among 215 Saudi Arabian patients with neurodevelopmental and autism spectrum disorders, we identified 33 patients with RTT who were subsequently examined by genome-wide transcriptome and mitochondrial genome variations. To the best of our knowledge, this is the first in-depth molecular and multiomics analyses of a large cohort of Saudi RTT cases with a view to informing the underlying mechanisms of this disease that impact many patients and families worldwide. The patients were unrelated, except for 2 affected sisters, and comprised of 25 classic and eight atypical RTT cases. The cases were screened for methyl-CpG binding protein 2 (MECP2), CDKL5, FOXG1, NTNG1, and mitochondrial DNA (mtDNA) variants, as well as copy number variations (CNVs) using a genome-wide experimental strategy. We found that 15 patients (13 classic and two atypical RTT) have MECP2 mutations, 2 of which were novel variants. Two patients had novel FOXG1 and CDKL5 variants (both atypical RTT). Whole mtDNA sequencing of the patients who were MECP2 negative revealed two novel mtDNA variants in two classic RTT patients. Importantly, the whole-transcriptome analysis of our RTT patients' blood and further comparison with previous expression profiling of brain tissue from patients with RTT revealed 77 significantly dysregulated genes. The gene ontology and interaction network analysis indicated potentially critical roles of MAPK9, NDUFA5, ATR, SMARCA5, RPL23, SRSF3, and mitochondrial dysfunction, oxidative stress response and MAPK signaling pathways in the pathogenesis of RTT genes. This study expands our knowledge on RTT disease networks and pathways as well as presents novel mutations and mtDNA alterations in RTT in a population sample that was not previously studied.

X-linked intellectual disability: Phenotypic expression in carrier females

To better understand the landscape of female phenotypic expression in X-linked intellectual disability (XLID), we surveyed the literature for female carriers of XLID gene alterations (n = 1098) and combined this with experience evaluating XLID kindreds at the Greenwood Genetic Center (n = 341) and at the University of Adelaide (n = 157). One-hundred forty-four XLID genes were grouped into nine categories based on the level of female phenotypic expression, ranging from no expression to female only expression. For each gene, the clinical presentation, gene expression in blood, X-inactivation (XI) pattern, biological pathway involved, and whether the gene escapes XI were noted. Among the XLID conditions, 88 (61.1%) exhibited female cognitive phenotypic expression only, while 56 (38.9%) had no female phenotypic expression (n = 45), phenotype expression with normal cognition in females (n = 8), or unknown status for female phenotypic expression (n = 3). In twenty-four (16.6%) XLID genes, XI was consistently skewed in female carriers, in 54 (37.5%) XI showed variable skewing, and in 33 (22.9%) XI was consistently random. The XI pattern was unknown in 33 (22.9%) XLID conditions. Therefore, there is evidence of a female carrier phenotype in the majority of XLID conditions although how exactly XI patterns influence the female phenotype in XLID conditions remains unclear.

Antiglycative Activity and RAGE Expression in Rett Syndrome

Rett syndrome (RTT) is a human neurodevelopmental disorder, whose pathogenesis has been linked to both oxidative stress and subclinical inflammatory status (OxInflammation). Methylglyoxal (MG), a glycolytic by-product with cytotoxic and pro-oxidant power, is the major precursor in vivo of advanced glycation end products (AGEs), which are known to exert their detrimental effect via receptor- (e.g., RAGE) or non-receptor-mediated mechanisms in several neurological diseases. On this basis, we aimed to compare fibroblasts from healthy subjects (CTR) with fibroblasts from RTT patients (N = 6 per group), by evaluating gene/protein expression patterns, and enzymatic activities of glyoxalases (GLOs), along with the levels of MG-dependent damage in both basal and MG-challenged conditions. Our results revealed that RTT is linked to an alteration of the GLOs system (specifically, increased GLO2 activity), that ensures unchanged MG-dependent damage levels. However, RTT cells underwent more pronounced cell death upon exogenous MG-treatment, as compared to CTR, and displayed lower RAGE levels than CTR, with no alterations following MG-treatment, thus suggesting that an adaptive response to dicarbonyl stress may occur. In conclusion, besides OxInflammation, RTT is associated with reshaping of the major defense systems against dicarbonyl stress, along with an altered cellular stress response towards pro-glycating insults.

An early seizure variant type of a male Rett syndrome patient with a MECP2 p.Arg133His missense mutation

BACKGROUND

The clinical spectrum of Rett syndrome (RTT; Mendelian Inheritance in Man [MIM] #312750) in males is considered to be wider than previously expected. Therefore, the existence of RTT with a normal male karyotype is still controversial. Here, we report the first case of a male patient presenting with an early seizure type of Rett-like phenotypes with a missense variant of MECP2.

METHOD

An 8-month-old male was admitted to the pediatric department due to an initial seizure event following aspiration pneumonia and was referred to our clinic for the evaluation of unexplained neuroregression. Genomic DNA was prepared from venous blood by standard procedures and was processed at the Yale Center for Genome Analysis (YCGA) for whole exome sequencing (WES). Processing of sequence data, variant calling, and the identification of de novo mutations were then performed. Direct Sanger sequencing was performed following PCR amplification.

RESULT

In this patient with a normal karyotype, WES analysis led to the identification of a novel, de novo missense variant of MECP2 (p.Arg133His) that is not observed in the normal population.

CONCLUSION

This rare case of an p.Arg133His hemizygous MECP2 missense mutation could guide future treatment and follow-up plans for RETT-like phenotypes.

Rett Syndrome: Treatment with IGF-I, Melatonin, Blackcurrant Extracts, and Rehabilitation

(1) This study describes the good evolution of a 6-year-old girl genetically diagnosed (R106X) with Rett syndrome (RTT), after having been treated with IGF-I, melatonin (MT), blackcurrant extracts (BC) and rehabilitated for 6 months. (2) The patient stopped normal development in the first year of age. The patient showed short stature and weight and fulfilled the main criteria for typical RTT. Despite her young age, there was pubic hair (Tanner II), very high plasma testosterone, and low levels of plasma gonadotrophins. There were no adrenal enzymatic deficits, and abdominal ultrasound studies were normal. The treatment consisted of IGF-I (0.04 mg/kg/day, 5 days/week, subcutaneous (sc)) for 3 months and then 15 days of rest, MT (50 mg/day, orally, without interruption) and neurorehabilitation. A new blood test, after 3 months of treatment, was absolutely normal and the pubic hair disappeared (Tanner I). Then, a new treatment was started with IGF-I, MT, and BC for another 3 months. In this period, the degree of pubertal development increased to Tanner III (pubic level), without a known cause. (3) The treatment followed led to clear improvements in most of the initial abnormalities, perhaps due to the neurotrophic effect of IGF-I, the antioxidant effects of MT and BC, and the cerebral increase in the cyclic glycine-proline (cGP) achieved with administration of BC. (4) A continuous treatment with IGF-I, MT, and BC appears to be useful in RTT.

Spectrum of MECP2 mutations in Vietnamese patients with RETT syndrome

Background

Rett syndrome (RTT) is a severe neurodevelopmental disorder in children characterized by a normal neurodevelopmental process in the first 6–18 months followed by a period of motor and vocal deterioration with stereotypic hand movements. Incidence of RTT is mostly due to de novo mutation in the MECP2 gene (methyl-CpG-binding protein 2).

Methods

The study assessed 27 female patients presented with classical RTT phenotype age range from 18 months to 48 months. Specialist carried out the clinical evaluation and diagnosis according to RTT diagnosis criteria. Blood samples from patients were then collected for genomic DNA extraction. We next performed MECP2 gene amplification and sequencing of the whole coding region to screen for mutations.

Result

MECP2 mutation was found in 20 patients (74%) including: 2 missense, 4 nonsense, 6 frameshift and 2 deletion mutation. The study identified 14 pathogenic mutations which we found 4 mutation, to our knowledge and extensive search, not priory reported in any mutation database or publication: c.1384-1385DelGT, c.1205insT, c.717delC and c.1132_1207del77. High percentage of C > T (70%) in CpG sites mutation was found.

Conclusion

Our result reveals a high percentage of C > T mutation in CpG hot spot, which is more prone to modification and more likely to be detected in RTT as a disorder is strictly due to de novo mutations. The study is the first to identify the mutation spectrum of MECP2 gene in Vietnamese patients and also an important step toward better diagnosis and care for RTT patients in Vietnam.

Are dopamine receptor and transporter changes in Rett syndrome reflected in Mecp2-deficient mice?

We tested the claim that the dopaminergic dysfunction of Rett Syndrome (RTT) also occurs in Mecp2-deficient mice that serve as a model of the syndrome. We used positron emission tomography (PET) to image dopamine D₂ receptors (D₂R) and transporters (DAT) in women with RTT and in Mecp2-deficient mice, and D₁R and D₂R density was measured in postmortem human tissue by autoradiography. Results showed 1) significantly reduced D₂R density in the striatum of women with RTT compared to control subjects. 2) PET imaging of mouse striatum similarly demonstrated significant reductions in D₂R density of 7-10 week-old hemizygous (Mecp2-null) and heterozygous (HET) mice compared to wild type (WT) mice. With age, the density of D₂R declined in WT mice but not HET mice. 3) In contrast, postmortem autoradiography revealed no group differences in the density of D₁R and D₂R in the caudate and putamen of RTT versus normal control subjects. 4) In humans and in the mouse model, PET revealed only marginal group differences in DAT. The results confirm that dopaminergic dysfunction in RTT is also present in Mecp2-deficient mice and that reductions in D₂R more likely explain the impaired ambulation and progressive rigidity observed rather than alterations in DAT.

[The course and the development of epilepsy in patients with typical variant of Rett syndrome and mutations]

AIM

Studying data of anamnesis, clinical state, electro-encephalographic, brain MRI in patients with Rett syndrome (МЕСР2).

MATERIAL AND METHODS

We studied 11 patients (female) from three to 23 years old with Rett syndrome and MeCP2 mutations. Observation continued 10 years (2006-2015). We analyzed the results of the neurological status, night sleep video-EEG monitoring, MRI.

RESULTS AND CONCLUSION

Epilepsy diagnosed in six cases (54, 5%). The overage age of debut of epileptic seizures was 3 years 9 months. There are some types of seizures: generalized, myoclonic, myotonic, tonic, versive, focal motor, atypical absences. Status epilepticus evolved in one patient. Generalized seizures were 56, 25%, focal seizures - 43, 75%. EEG changing marked in nine patients (81, 8%): slowdown back activity, episodes of periodic regional slowdown, regional epileptiform activity, and diffuse epileptiform activity like benign focal epileptiform discharges (BFED). five patients took antiepileptic drugs. All of them had improved during treatment. There were reducing of frequency of the seizures up 50% - 4 cases (80%). one patients with resistant epilepsy was taken combination of drugs (levetirecetam, topiromat, zonisamide, benzodiazepine) with stopping of seizures in the night sleep and decreasing of frequency of daytime seizures to 50%. We believe there is very important of study epilepsy in patients with Rett syndrome and improvement of its treatment.

[The course and development of epilepsy in patients with typical variant of Rett syndrome and mutations]

AIM

To study the anamnesis, clinical state, electro-encephalographic and brain MRI characteristics in patients with Rett syndrome (МЕСР2) and epilepsy.

MATERIAL AND METHODS

Eleven female patients, aged from 3 to 23 years, with Rett syndrome and MeCP2 mutations were studied. The study continued for 10 years (2006-2015). Assessment of neurological and mental status, night sleep video-EEG monitoring, MRI were performed.

RESULTS AND CONCLUSION

Epilepsy was diagnosed in six cases (54.5%). Mean age at onset of epileptic seizures was 3 years 9 month. The following types of seizures were described: generalized, myoclonic, myotonic, tonic, versive, focal motor, atypical absences. Status epilepticus developed in one patient. Generalized seizures were identified in 56.25%, focal seizures in 43.75%. EEG changes were found in 9 patients (81.8%): slowing of the activity, episodes of periodic regional slowing, regional epileptiform activity and diffuse epileptiform activity, benign focal epileptiform discharges (BFED) of childhood, multiregional epileptiform activity. Five patients were treated with antiepileptic drugs. All of them had improved during treatment: a reduction of frequency of seizures was up to 50% in 4 cases (80%). One patient with resistant epilepsy was treated with the combination of drugs (levetiracetam, topiramate, zonisamide, benzodiazepine) that led to stopping of seizures during night sleep and decrease in the frequency of daytime seizures by 50%. Further research of epilepsy and efficacy of antiepileptic drugs in Rett syndrome is required.

Randomized open-label trial of dextromethorphan in Rett syndrome

OBJECTIVE

To determine safety and perform a preliminary assessment of dose-dependent efficacy of dextromethorphan in normalizing electrographic spikes, clinical seizures, and behavioral and cognitive functions in girls with Rett syndrome.

METHODS

We used a prospective randomized, open-label trial in fast metabolizers of dextromethorphan to examine the effect of dextromethorphan on core clinical features of Rett syndrome. Interictal spike activity and clinical seizures were determined using EEG and parent reporting. Cognitive data were obtained using the Mullen Scales of Early Learning and Vineland Adaptive Behavior Scales, while behavioral data were obtained from parent-completed checklists, the Aberrant Behavior Checklist-Community Version, and the Screen for Social Interaction. Anthropometric data were obtained according to the National Health and Nutrition Examination Survey. The Rett Syndrome Severity Scale provided a clinical global impression of the effect of dextromethorphan on clinical severity.

RESULTS

Dextromethorphan is safe for use in 3- to 15-year-old girls with Rett syndrome. Thirty-five girls were treated with 1 of 3 doses of dextromethorphan over a period of 6 months. Statistically significant dose-dependent improvements were seen in clinical seizures, receptive language, and behavioral hyperactivity. There was no significant improvement in global clinical severity as measured by the Rett Syndrome Severity Scale.

CONCLUSIONS

Dextromethorphan is a potent noncompetitive antagonist of the NMDA receptor channel that is safe for use in young girls with Rett syndrome. Preliminary evidence suggests that dextromethorphan may improve some core features of Rett syndrome.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that dextromethorphan at various doses does not change EEG spike counts over 6 months, though precision was limited to exclude an important effect.

Dysregulation of Alternative Poly-adenylation as a Potential Player in Autism Spectrum Disorder

We present here the hypothesis that alternative poly-adenylation (APA) is dysregulated in the brains of individuals affected by Autism Spectrum Disorder (ASD), due to disruptions in the calcium signaling networks. APA, the process of selecting different poly-adenylation sites on the same gene, yielding transcripts with different-length 3′ untranslated regions (UTRs), has been documented in different tissues, stages of development and pathologic conditions. Differential use of poly-adenylation sites has been shown to regulate the function, stability, localization and translation efficiency of target RNAs. However, the role of APA remains rather unexplored in neurodevelopmental conditions. In the human brain, where transcripts have the longest 3′ UTRs and are thus likely to be under more complex post-transcriptional regulation, erratic APA could be particularly detrimental. In the context of ASD, a condition that affects individuals in markedly different ways and whose symptoms exhibit a spectrum of severity, APA dysregulation could be amplified or dampened depending on the individual and the extent of the effect on specific genes would likely vary with genetic and environmental factors. If this hypothesis is correct, dysregulated APA events might be responsible for certain aspects of the phenotypes associated with ASD. Evidence supporting our hypothesis is derived from standard RNA-seq transcriptomic data but we suggest that future experiments should focus on techniques that probe the actual poly-adenylation site (3′ sequencing). To address issues arising from the use of post-mortem tissue and low numbers of heterogeneous samples affected by confounding factors (such as the age, gender and health of the individuals), carefully controlled in vitro systems will be required to model the effect of calcium signaling dysregulation in the ASD brain.

Early motor phenotype detection in a female mouse model of Rett syndrome is improved by cross-fostering

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused by mutations in the gene encoding methyl CpG binding protein 2 (MeCP2) that occur sporadically in 1:10,000 female births. RTT is characterized by a period of largely normal development followed by regression in language and motor skills at 6-18 months of age. Mecp2 mutant mice recapitulate many of the clinical features of RTT, but the majority of behavioral assessments have been conducted in male Mecp2 hemizygous null mice as offspring of heterozygous dams. Given that RTT patients are predominantly female, we conducted a systematic analysis of developmental milestones, sensory abilities, and motor deficits, following the longitudinal decline of function from early postnatal to adult ages in female Mecp2 heterozygotes of the conventional Bird line (Mecp2tm1.1bird-/+), as compared to their female wildtype littermate controls. Further, we assessed the impact of postnatal maternal environment on developmental milestones and behavioral phenotypes. Cross-fostering to CD1 dams accelerated several developmental milestones independent of genotype, and induced earlier onset of weight gain in adult female Mecp2tm1.1bird-/+ mice. Cross-fostering improved the sensitivity of a number of motor behaviors that resulted in observable deficits in Mecp2tm1.1bird-/+ mice at much earlier (6-7 weeks) ages than were previously reported (6-9 months). Our findings indicate that female Mecp2tm1.1bird-/+ mice recapitulate many of the motor aspects of RTT syndrome earlier than previously appreciated. In addition, rearing conditions may impact the phenotypic severity and improve the ability to detect genotype differences in female Mecp2 mutant mice.

Evaluation of QTc in Rett syndrome: Correlation with age, severity, and genotype

Rett syndrome (RTT) is caused by MECP2 mutations, resulting in various neurological symptoms. Prolonged corrected QT interval (QTc) is also reported and is a speculated cause of sudden death in RTT. The purpose of this study was to correlate QTc in RTT patients with age, clinical severity, and genotype. 100 RTT patients (98 females, 2 males) with MECP2 mutations underwent baseline neurological evaluation (KKI-RTT Severity Scale) and QTc measurement (standard 12 lead electrocardiogram) as part of our prospective natural history study. Mean QTc of the cohort was 422.6 msec, which did not exceed the normal values for age. 7/100 patients (7%) had QTc prolongation (>450 msec). There was a trend for increasing QTc with age and clinical severity (P = 0.09). No patients with R106C, R106W, R133C, R168*, R270*, R294*, R306C, R306H, and R306P mutations demonstrated QTc prolongation. There was a relatively high proportion of QTc prolongation in patients with R255* mutations (2/8, 25%) and large deletions (1/4, 25%). The overall presence of QTc prolongation did not correlate with mutation category (P = 0.52). Our findings demonstrate that in RTT, the prevalence of QTc prolongation is lower than previously reported. Hence, all RTT patients warrant baseline ECG; if QTc is prolonged, then cardiac followup is warranted. If initial QTc is normal, then annual ECGs, particularly in younger patients, may not be necessary. However, larger sample sizes are needed to solidify the association between QTc and age and clinical severity. The biological and clinical significance of mild QTc prolongation above the normative data remains undetermined.

Analysis of the Serotonergic System in a Mouse Model of Rett Syndrome Reveals Unusual Upregulation of Serotonin Receptor 5b

Mutations in the transcription factor methyl-CpG-binding-protein 2 (MeCP2) cause a delayed-onset neurodevelopmental disorder known as Rett syndrome (RTT). Although alteration in serotonin levels have been reported in RTT patients, the molecular mechanisms underlying these defects are not well understood. Therefore, we chose to investigate the serotonergic system in hippocampus and brainstem of male Mecp2^-/y knock-out mice in the B6.129P2(C)-Mecp2(tm1.1Bird) mouse model of RTT. The serotonergic system in mouse is comprised of 16 genes, whose mRNA expression profile was analyzed by quantitative RT-PCR. Mecp2^-/y mice are an established animal model for RTT displaying most of the cognitive and physical impairments of human patients and the selected areas receive significant modulation through serotonin. Using anatomically and functional characterized areas, we found region-specific differential expression between wild type and Mecp2^-/y mice at post-natal day 40. In brainstem, we found five genes to be dysregulated, while in hippocampus, two genes were dysregulated. The one gene dysregulated in both brain regions was dopamine decarboxylase, but of special interest is the serotonin receptor 5b (5-ht_5b), which showed 75-fold dysregulation in brainstem of Mecp2^-/y mice. This dysregulation was not due to upregulation, but due to failure of down-regulation in Mecp2^-/y mice during development. Detailed analysis of 5-ht_5b revealed a receptor that localizes to endosomes and interacts with G_αi proteins.

Clinical and biological progress over 50 years in Rett syndrome

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

GlyT2-Dependent Preservation of MECP2-Expression in Inhibitory Neurons Improves Early Respiratory Symptoms but Does Not Rescue Survival in a Mouse Model of Rett Syndrome

Mutations in methyl-CpG-binding protein 2 (MECP2) gene have been shown to manifest in a neurodevelopmental disorder that is called Rett syndrome. A typical problem that occurs during development is a disturbance of breathing. To address the role of inhibitory neurons, we generated a mouse line that restores MECP2 in inhibitory neurons in the brainstem by crossbreeding a mouse line that expresses the Cre-recombinase (Cre) in inhibitory neurons under the control of the glycine transporter 2 (GlyT2, slc6a5) promotor (GlyT2-Cre) with a mouse line that has a floxed-stop mutation of the Mecp2 gene (Mecp2^stop/y). Unrestrained whole-body-plethysmography at postnatal day P60 revealed a low respiratory rate and prolonged respiratory pauses in Mecp2^stop/y mice. In contrast, GlyT2-Cre positive Mecp2^stop/y mice (Cre⁺; Mecp2^stop/y) showed greatly improved respiration and were indistinguishable from wild type littermates. These data support the concept that alterations in inhibitory neurons are important for the development of the respiratory phenotype in Rett syndrome.

Brief report: systematic review of Rett syndrome in males

Rett syndrome (RTT) is a neurogenetic disorder in which a period of typical development is followed by loss of previously acquired skills. Once thought to occur exclusively in females, increasing numbers of male cases of RTT have been reported. This systematic review included 36 articles describing 57 cases of RTT in males. Mutations of the MECP2 gene were present in 56 % of cases, and 68 % of cases reported other genetic abnormalities. This is the first review of published reports of RTT in male patients.

Functional Profiling of Human MeCP2 by Automated Data Comparison Analysis and Computerized Expression Pathway Modeling

OBJECTIVES

Methyl-CpG binding protein 2 (MeCP2) is a ubiquitous epigenetic factor that represses gene expression by modifying chromatin. Mutations in the MeCP2 gene cause Rett syndrome, a progressive neurodevelopmental disorder. Recent studies also have shown that MeCP2 plays a role in carcinogenesis. Specifically, functional ablation of MeCP2 suppresses cell growth and leads to the proliferation of cancer cells. However, MeCP2's function in adult tissues remains poorly understood. We utilized a weight matrix-based comparison software to identify transcription factor binding site (TFBS) of MeCP2-regulated genes, which were recognized by cDNA microarray analysis.

METHODS

MeCP2 expression was silenced using annealed siRNA in HEK293 cells, and then a cDNA microarray analysis was performed. Functional analysis was carried out, and transcriptional levels in target genes regulated by MeCP2 were investigated. TFBS analysis was done within genes selected by the cDNA microarray analysis, using a weight matrix-based program and the TRANSFAC 6.0 database.

RESULTS

Among the differentially expressed genes with a change in expression greater than two-fold, 189 genes were up-regulated and 91 genes were down-regulated. Genes related to apoptosis and cell proliferation (JUN, FOSL2, CYR61, SKIL, ATF3, BMABI, BMPR2, RERE, and FALZ) were highly up-regulated. Genes with anti-apoptotic and anti-proliferative functions (HNRPA0, HIS1, and FOXC1) were down-regulated. Using TFBS analysis within putative promoters of novel candidate target genes of MeCP2, disease-related transcription factors were identified.

CONCLUSIONS

The present results provide insights into the new target genes regulated by MeCP2 under epigenetic control. This information will be valuable for further studies aimed at clarifying the pathogenesis of Rett syndrome and neoplastic diseases.

X inactivation and reactivation in X-linked diseases

X chromosome inactivation (XCI) is the phenomenon by which mammals compensate for dosage of X-linked genes in females (XX) versus males (XY). XCI patterns can be random or show extreme skewing, and can modify the mode of inheritance of X-driven phenotypes, which contributes to the variability of human pathologies. Recent findings have shown reversibility of the XCI process, which has opened new avenues in the approaches used for the treatment of X-linked diseases.

Clinical Genetic Aspects of ASD Spectrum Disorders

Early presumptions opined that autism spectrum disorder (ASD) was related to the rearing of these children by emotionally-distant mothers. Advances in the 1960s and 1970s clearly demonstrated the biologic basis of autism with a high heritability. Recent advances have demonstrated that specific etiologic factors in autism spectrum disorders can be identified in 30%–40% of cases. Based on early reports newer, emerging genomic technologies are likely to increase this diagnostic yield to over 50%. To date these investigations have focused on etiologic factors that are largely mono-factorial. The currently undiagnosed causes of ASDs will likely be found to have causes that are more complex. Epigenetic, multiple interacting loci, and four dimensional causes (with timing as a variable) are likely to be associated with the currently unidentifiable cases. Today, the “Why” is more important than ever. Understanding the causes of ASDs help inform families of important issues such as recurrence risk, prognosis, natural history, and predicting associated co-morbid medical conditions. In the current era of emerging efforts in “personalized medicine”, identifying an etiology will be critical in identifying endo-phenotypic groups and individual variations that will allow for tailored treatment for persons with ASD.

Homozygous c.1160C>T (P38L) in the MECP2 gene in a female Rett syndrome patient

Rett syndrome is a severe X-linked dominant neurodevelopmental disorder. Mutations in the MECP2 gene on chromosome Xq28 have been shown to be the cause of Rett syndrome. Sequencing of the MECP2 gene in a patient with clinical suspicion of Rett syndrome revealed c.1160C>T (P387L) in exon 4 of the MECP2 gene homozygously. Females with Rett syndrome are usually heterozygous for a mutation in MECP2. Uniparental disomy as a probable cause for the homozygous presence of this mutation was ruled out by quantitative fluorescence-polymerase chain reaction. Moreover to our knowledge this mutation has only been reported in males with X-linked mental retardation (MRX). We hypothesize that the presence of this mutation c.1160C>T (P387L) in the homozygous form is responsible for the Rett syndrome-like phenotype seen in this patient. This novel report reveals for the first time the homozygous presence of a mutation which has hitherto only been reported in males with MRX.

Functional outcomes in Rett syndrome

AIM

To relate functional outcomes to mutation type and age at evaluation in patients with Rett syndrome (RTT).

METHOD

We identified 96 RTT patients with mutations in the MECP2 (methyl-CpG-binding protein 2) gene. Chart analysis, clinical evaluation, and functional measures were completed.

RESULTS

Among 11 mutation groups, a statistically significant group effect of mutation type was observed for self-care, upper extremity function, and mobility, on standardized measures administered by occupational and physical therapists. Patients with R133C and uncommon mutations tended to perform best on upper extremity and self-care items, whereas patients with R133C, R306C and R294X had the highest scores on the mobility items. The worst performers on upper extremity and self-care items were patients with large deletions, R255X, R168X, and T158M mutations. The lowest scores for mobility were found in patients with T158M, R255X, R168X, and R270X mutations. On categorical variables as reported by parents at the time of initial evaluation, patients with R133C and R294X were most likely to have hand use, those with R133C, R294X, R306C and small deletions were most likely to be ambulatory, and those with R133C were most likely to be verbal.

INTERPRETATION

Functional performance in RTT patients may relate to the type of mutation. Knowledge of these relationships is useful for developing appropriate rehabilitation strategies and prognosis.

Variant Rett syndrome in a girl with a pericentric X-chromosome inversion leading to epigenetic changes and overexpression of the MECP2 gene

Rett syndrome is a neurodevelopmental disorder caused by mutations in the MECP2 gene. We investigated the genetic basis of disease in a female patient with a Rett-like clinical. Karyotype analysis revealed a pericentric inversion in the X chromosome -46,X,inv(X)(p22.1q28), with breakpoints in the cytobands where the MECP2 and CDKL5 genes are located. FISH analysis revealed that the MECP2 gene is not dislocated by the inversion. However, and in spite of a balanced pattern of X inactivation, this patient displayed hypomethylation and an overexpression of the MECP2 gene at the mRNA level in the lymphocytes (mean fold change: 2.55±0.38) in comparison to a group of control individuals; the expression of the CDKL5 gene was similar to that of controls (mean fold change: 0.98±0.10). No gains or losses were detected in the breakpoint regions encompassing known or suspected transcription regulatory elements. We propose that the de-regulation of MECP2 expression in this patient may be due to alterations in long-range genomic interactions caused by the inversion and hypothesize that this type of epigenetic de-regulation of the MECP2 may be present in other RTT-like patients.

Rett Syndrome: Reaching for Clinical Trials

Rett syndrome (RTT) is a syndromic autism spectrum disorder caused by loss-of-function mutations in MECP2. The methyl CpG binding protein 2 binds methylcytosine and 5-hydroxymethycytosine at CpG sites in promoter regions of target genes, controlling their transcription by recruiting co-repressors and co-activators. Several preclinical studies in mouse models have identified rational molecular targets for drug therapies aimed at correcting the underlying neural dysfunction. These targeted therapies are increasingly translating into human clinical trials. In this review, we present an overview of RTT and describe the current state of preclinical studies in methyl CpG binding protein 2-based mouse models, as well as current clinical trials in individuals with RTT.

Rett syndrome and MeCP2

Rett syndrome (RTT) is a severe and progressive neurological disorder, which mainly affects young females. Mutations of the methyl-CpG binding protein 2 (MECP2) gene are the most prevalent cause of classical RTT cases. MECP2 mutations or altered expression are also associated with a spectrum of neurodevelopmental disorders such as autism spectrum disorders with recent links to fetal alcohol spectrum disorders. Collectively, MeCP2 relation to these neurodevelopmental disorders highlights the importance of understanding the molecular mechanisms by which MeCP2 impacts brain development, mental conditions, and compromised brain function. Since MECP2 mutations were discovered to be the primary cause of RTT, a significant progress has been made in the MeCP2 research, with respect to the expression, function and regulation of MeCP2 in the brain and its contribution in RTT pathogenesis. To date, there have been intensive efforts in designing effective therapeutic strategies for RTT benefiting from mouse models and cells collected from RTT patients. Despite significant progress in MeCP2 research over the last few decades, there is still a knowledge gap between the in vitro and in vivo research findings and translating these findings into effective therapeutic interventions in human RTT patients. In this review, we will provide a synopsis of Rett syndrome as a severe neurological disorder and will discuss the role of MeCP2 in RTT pathophysiology.

Role of conserved cis-regulatory elements in the post-transcriptional regulation of the human MECP2 gene involved in autism

BACKGROUND

The MECP2 gene codes for methyl CpG binding protein 2 which regulates activities of other genes in the early development of the brain. Mutations in this gene have been associated with Rett syndrome, a form of autism. The purpose of this study was to investigate the role of evolutionarily conserved cis-elements in regulating the post-transcriptional expression of the MECP2 gene and to explore their possible correlations with a mutation that is known to cause mental retardation.

RESULTS

A bioinformatics approach was used to map evolutionarily conserved cis-regulatory elements in the transcribed regions of the human MECP2 gene and its mammalian orthologs. Cis-regulatory motifs including G-quadruplexes, microRNA target sites, and AU-rich elements have gained significant importance because of their role in key biological processes and as therapeutic targets. We discovered in the 5'-UTR (untranslated region) of MECP2 mRNA a highly conserved G-quadruplex which overlapped a known deletion in Rett syndrome patients with decreased levels of MeCP2 protein. We believe that this 5'-UTR G-quadruplex could be involved in regulating MECP2 translation. We mapped additional evolutionarily conserved G-quadruplexes, microRNA target sites, and AU-rich elements in the key sections of both untranslated regions. Our studies suggest the regulation of translation, mRNA turnover, and development-related alternative MECP2 polyadenylation, putatively involving interactions of conserved cis-regulatory elements with their respective trans factors and complex interactions among the trans factors themselves. We discovered highly conserved G-quadruplex motifs that were more prevalent near alternative splice sites as compared to the constitutive sites of the MECP2 gene. We also identified a pair of overlapping G-quadruplexes at an alternative 5' splice site that could potentially regulate alternative splicing in a negative as well as a positive way in the MECP2 pre-mRNAs.

CONCLUSIONS

A Rett syndrome mutation with decreased protein expression was found to be associated with a conserved G-quadruplex. Our studies suggest that MECP2 post-transcriptional gene expression could be regulated by several evolutionarily conserved cis-elements like G-quadruplex motifs, microRNA target sites, and AU-rich elements. This phylogenetic analysis has provided some interesting and valuable insights into the regulation of the MECP2 gene involved in autism.

MECP2 gene study in a large cohort: testing of 240 female patients and 861 healthy controls (519 females and 342 males)

The MECP2 gene located on Xq28 is one of the most important genes contributing to the spectrum of neurodevelopmental disorders. Therefore, we present our experience in the molecular study of this gene. MECP2 was thoroughly tested for the presence of mutations (sequencing of four exons and rearrangements) in 120 female patients: 28 with classic Rett syndrome, five with atypical Rett syndrome, and 87 with heterogeneous phenotypes with some Rett-like features. Another 120 female patients with intellectual disability of unknown origin were also studied, but in these cases we only tested exons 3 and 4. Finally, 861 healthy controls (519 females and 342 males) were also studied for exon 3 and 4. Eighteen different pathological mutations were found, five of them previously undescribed, and four large deletions detected by multiplex ligation-dependent probe amplification. All were de novo mutations not present in the parents. In conclusion, i) MECP2 is one of the most important genes in the diagnosis of genetic intellectual disability in females; ii) MECP2 must be studied not only in patients with classical/atypical Rett syndrome but also in patients with other phenotypes related to Rett syndrome; and iii) for the new variants, it is important to perform complementary studies, including the analysis of large populations of healthy individuals and the use of in silico programs.

The relationship of Rett syndrome and MECP2 disorders to autism

Rett syndrome (RTT, MIM#312750) is a neurodevelopmental disorder that is classified as an autism spectrum disorder. Clinically, RTT is characterized by psychomotor regression with loss of volitional hand use and spoken language, the development of repetitive hand stereotypies, and gait impairment. The majority of people with RTT have mutations in Methyl-CpG-binding Protein 2 (MECP2), a transcriptional regulator. Interestingly, alterations in the function of the protein product produced by MECP2, MeCP2, have been identified in a number of other clinical conditions. The many clinical features found in RTT and the various clinical problems that result from alteration in MeCP2 function have led to the belief that understanding RTT will provide insight into a number of other neurological disorders. Excitingly, RTT is reversible in a mouse model, providing inspiration and hope that such a goal may be achieved for RTT and potentially for many neurodevelopmental disorders.

Videofluororadiographic Descriptors of Swallowing Physiology in Typical Rett Syndrome: Post-Regression Stabilization During Early Childhood

Typical or classic Rett syndrome (RTT) is the only pervasive neurodevelopmental disorder with a known chromosomal abnormality. Despite differences in clinical phenotype of girls with RTT who share the same gene mutation on chromosome X, there is commonality in the stages and core features of this profoundly disabling disorder, including the deterioration of acquired vocal behaviors and meaningful speech during the regression stage. The purpose of this article is to ascertain any commonality in the swallowing neurophysiology of a select sample of girls with typical RTT who were under the age of 5 years and had undergone the devastating effects of developmental regression.

Updates in the genetic evaluation of the child with global developmental delay or intellectual disability

Global developmental delay (GDD) and intellectual disability (ID) occur in up to 3% of the general population and are even more commonly encountered in the setting of the pediatric neurology clinic. New advances in technology and in the understanding of genetic disorders have led to changes in the diagnostic approach to a child with unexplained GDD or ID. Chromosomal microarray has become a first-line test for evaluation of patients in this population and has both significantly increased diagnostic yield and introduced new challenges in the interpretation of copy number variants of uncertain significance. The G-banded karyotype is now frequently utilized as an adjunct to the microarray rather than as a first-line test in individuals with GDD or ID. Fragile X DNA testing continues to be recommended in the initial evaluation of the child with GDD or ID. The presence or absence of certain cardinal features (such as microcephaly or macrocephaly, seizures, autism, abnormal neurologic examination, and facial dysmorphism) can be utilized to direct single-gene molecular testing. The availability of next-generation and massively parallel sequencing technologies has enabled the use of genetic testing panels, in which dozens of genes associated with GDD or ID may be rapidly analyzed. Most recently, the clinical availability of whole-genome and whole-exome sequencing has opened new possibilities for the evaluation of individuals with GDD or ID who have previously eluded a genetic diagnosis. Consultation with a medical geneticist is recommended when progressing beyond first-tier analyses to most efficiently prioritize testing.

Apneic crises: a clue for MECP2 testing in severe neonatal hypotonia-respiratory failure

Males with methyl-CpG-binding protein 2 (MECP2) mutations may present with neonatal encephalopathy. We report on an infant with a MECP2 mutation who exhibited complex constellation of symptoms, including severe hypotonia, respiratory failure, and apneic episodes. In the neonatal period these symptoms are common to other disorders, including Ondine syndrome. Our observation confirms that the triad of severe hypotonia, apneic episodes, and respiratory failure may be caused by MECP2 mutations. Neonatologist and neuropediatricians must be alert to the presence of these symptoms to exclude this rare but severe disorder. Clinical suspicion and molecular confirmation of MECP2 mutation is of great importance for defining the diagnosis of this rare affection.

Molecular diagnostic dilemmas in Rett syndrome

Rett syndrome (OMIM 312750) is a progressive, X-linked neurodevelopmental disorder caused by mutations in the MECP2 gene located on chromosome Xq28. The disorder is characterized by a period of normal development during the first 6-18months of life, followed by gradual loss of skills already gained, such as speech and purposeful movement of the hands. The majority of cases are sporadic and represent "de novo" mutations. In this study we summarize the results of diagnostic testing of 30 patients with Rett syndrome (RTT) or mental retardation of unknown etiology using bidirectional sequencing of the open reading frame of the MECP2 gene. Twenty different variants were identified in those patients including 12 missense (R133C, P152R, T158M, V300I, I303M, R306C, T311M, R344W, A358T, P384L, A443T, V481M), four nonsense (R168X, K192X, R255X, R270X), two deletion (E137_L386del, I293_S350del), and two frameshift (S291QfsX26, G343AfsX6) mutations. Seven of the twenty variants identified were novel mutations (E137_L386del, K192X, S291QfsX26, G343AfsX6, I293_S350del, P384L, and A443T). In the cases with novel or non-recurrent missense mutations, family studies were performed to investigate genotype-phenotype correlations. Our results demonstrate the importance of family studies and highlight the complexity of interpretation of MECP2 alterations, which may or may not be disease-associated.

The role of oxidative stress in Rett syndrome: an overview

The main cause of Rett syndrome (RTT), a pervasive development disorder almost exclusively affecting females, is a mutation in the methyl-CpG binding protein 2 (MeCP2) gene. To date, no cure for RTT exists, although disease reversibility has been demonstrated in animal models. Emerging evidence from our and other laboratories indicates a potential role of oxidative stress (OS) in RTT. This review examines the current state of the knowledge on the role of OS in explaining the natural history, genotype-phenotype correlation, and clinical heterogeneity of the human disease. Biochemical evidence of OS appears to be related to neurological symptom severity, mutation type, and clinical presentation. These findings pave the way for potential new genetic downstream therapeutic strategies aimed at improving patient quality of life. Further efforts in the near future are needed for investigating the yet unexplored "black box" between the MeCP2 gene mutation and subsequent OS derangement.

Molecular screening of MECP2 gene in a cohort of Lebanese patients suspected with Rett syndrome: report on a mild case with a novel indel mutation

BACKGROUND

Rett syndrome (RTT), an X-linked, dominant, neurodevelopment disorder represents 10% of female subjects with profound intellectual disability. Mutations in the MECP2 gene are responsible for up to 95% of the classical RTT cases, and nearly 500 different mutations distributed throughout the gene have been reported.

METHODS

We report here the molecular study of two isoforms, MECP2_e1 and MECP2_e2, in 45 Lebanese girls presenting developmental delay and at least one of the following features: microcephaly, neurodegeneration, abnormal behaviour, stereotypical hand movements, teeth grinding and difficulty in walking. Mutation screening was performed by denaturating high-performance liquid chromatography combined with direct sequencing.

RESULTS

Sixteen variants were noted, of which 14 have been previously reported: five suspected polymorphisms and nine mutations. Two variants were novel mutations in exon 4: c.1093_1095delGAG (p.E365del) and c.1164_1184delACCTCCACCTGAGCCCGAGAGinsCTGAGCCCCAGGACTTGAGCA (p.P388PfsX389). The deletion was found in an 8-year-old girl with typical clinical features of RTT. The indel was found in a 6-year-old girl with a very mild phenotype.

CONCLUSION

Genotype/phenotype correlation is discussed and the importance of a molecular study of MECP2 gene in patients with very mild features or a regression after the age of 2 is raised.