Genetic and epileptic features in Rett syndrome

Variation spectrum of MECP2 in Korean patients with Rett and Rett-like syndrome: a literature review and reevaluation of variants based on the ClinGen guideline

Rett syndrome (RTT) is a progressive neurodevelopmental disorder caused by variants in MECP2. Emerging evidence of ethnic specificity of genetic variations has allowed precise diagnostic approaches with tailored therapies. In this study, we reviewed the variation spectrum of MECP2 in Korean RTT(-like) patients and compared it with previous reports in multiple ethnic groups. We reevaluated variants found in Korean RTT patients according to the new Clinical Genome Resource guideline to reinterpret and reclassify variants of uncertain significance in MECP2. Among 377 cases, 56 (14.9%) showed pathogenic variants, and three novel variants, p.(Ala277Argfs*7), p.(Ala378Glyfs*8), and p.(Arg270_Ser332del), were identified. Comprehensive data from Korea revealed an overall consistent variation spectrum with those from other ethnicities. Through the reevaluation of variants, nine that previously had insufficient evidence for pathogenicity were reclassified into pathogenic variants. Our study provided insight on the genetic contribution of MECP2 in RTT and a useful background for genetic counseling in the Korean population.

Clinical and Genetic Profile of Autism Spectrum Disorder-Epilepsy (ASD-E) Phenotype: Two Sides of the Same Coin!

The clinical phenotype of autism spectrum disorder and epilepsy (ASD-E) is a common neurological presentation in various genetic disorders, irrespective of the underlying pathophysiological mechanisms. Here we describe the demographic and clinical profiles, coexistent neurological conditions, type of seizures, epilepsy syndrome, and EEG findings in 11 patients with ASD-E phenotype with proven genetic etiology. The commonest genetic abnormality noted was CDKL5 mutation (3), MECP2 mutation (2), and 1p36 deletion (2). The median age of onset of clinical seizures was 6 months (range, 10 days to 11 years). The most common seizure type was focal onset seizures with impaired awareness, observed in 7 (63.6%) patients followed by epileptic spasms in 4 (30.8%), generalized tonic-clonic and atonic seizures in 3 (27.3%) patients each and tonic seizures in 2 (18.2%) patients and myoclonic seizures in 1 (9.1%) patient. Focal and multifocal interictal epileptiform abnormalities were seen in 6 (54.6%) and 5 (45.5%) patients, respectively. Epileptic encephalopathy and focal epilepsy were seen in 7 (63.6%) and 4 (36.4%) patients, respectively. The diagnostic yield of genetic testing was 44% (11 of 25 patients) and when variants of unknown significance and metabolic defects were included, the yield increased to 60% (15 of 25 patients). We conclude that in patients with ASD-E phenotype with an underlying genetic basis, the clinical seizure type, epilepsy syndrome, and EEG patterns are variable. Next-generation exome sequencing and chromosomal microarray need to be considered in clinical practice as part of evaluation of children with ASD-E phenotype.

Genetic and molecular basis of epilepsy-related cognitive dysfunction

Epilepsy is a common neurological disease characterized by recurrent seizures. About 70 million people were affected by epilepsy or epileptic seizures. Epilepsy is a complicated complex or symptomatic syndromes induced by structural, functional, and genetic causes. Meanwhile, several comorbidities are accompanied by epileptic seizures. Cognitive dysfunction is a long-standing complication associated with epileptic seizures, which severely impairs quality of life. Although the definitive pathogenic mechanisms underlying epilepsy-related cognitive dysfunction remain unclear, accumulating evidence indicates that multiple risk factors are probably involved in the development and progression of cognitive dysfunction in patients with epilepsy. These factors include the underlying etiology, recurrent seizures or status epilepticus, structural damage that induced secondary epilepsy, genetic variants, and molecular alterations. In this review, we summarize several theories that may explain the genetic and molecular basis of epilepsy-related cognitive dysfunction.

Clinical Feature and Genetics in Rett Syndrome: A Report on Iranian Patients

OBJECTIVES

Rett syndrome is characterized by normal development for the first 6-18 months of life followed by the loss of fine and gross motor skills and the ability to engage in social interaction. In most patients, mutations are found in methyl CpG-binding protein 2 (MECP2) gene. We investigated the relation between Rett clinical diagnosis and mutations in MECP2.

MATERIALS & METHODS

Children suspected of Rett syndrome were invited to participate in this study. Twenty-three patients from the Mofid Hospital, Tehran, Iran suffered from classic Rett syndrome diagnostic criteria were enrolled in 2012. The severity of symptoms was assessed for all of them. The peripheral blood samples were collected in EDTA tubes and the genomic DNA was extracted using standard salting out method. The mutation of MEPC2 gene was studied using DNA sequencing method.

RESULTS

Overall, 11(47.8%) patients had MECP2 gene mutation, while 12 cases (52.2%) had no mutations. Changes in genetics were associated with phenotypical manifestations. The most prevalent mutation was p.v288 mainly associated with partially or uncontrolled seizures.

CONCLUSION

For the first time, we studies the Rett syndrome in terms of clinical manifestations and genetic changes in Iran.

The Clinical Predictors That Facilitate a Clinician's Decision to Order Genetic Testing for Rett Syndrome

BACKGROUND

Rett syndrome is a common genetic cause of intellectual disability in girls caused by a mutation in the MECP2 gene. Diagnosis is based on clinical criteria. The aim was to compare the frequencies of the clinical criteria in patients with and without MECP2 mutations.

METHODS

We performed a retrospective review at a children's hospital of patients who underwent MECP2 testing from 2008 to 2013. Logistic regression was performed to determine which criteria were most predictive of MECP2 status.

RESULTS

Of 169 patients who met inclusion criteria, 46 (27.2%) were MECP2 positive. Loss of language skills (MECP2+ 100% versus MECP2- 87.8%; P = 0.012) was the most common finding among both groups. Other main criteria were more common in MECP2 patients: gait abnormalities (84.8% versus 27.6%; P < 0.0001); stereotypic hand movements (76.1% versus 15.5%; P < 0.0001); loss of hand skills (71.7% versus 4.9%; P < 0.0001). Logistic regression analysis including all four criteria demonstrated language loss was not predictive.

CONCLUSIONS

Loss of hand skills resulted in the highest odds of having a positive genetic test. Gait abnormalities and stereotypic hand movements were also strong predictors of MECP2+ testing. Many individuals with language delay had genetic testing; however, this is the least specific of the major criteria. These findings have implications for which patients should have genetic testing.

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.

Reduced seizure threshold and altered network oscillatory properties in a mouse model of Rett syndrome

Rett syndrome (RTT) is a disorder with a pronounced neurological phenotype and is caused mainly by mutations in the X-linked gene MECP2. A common feature of RTT is an abnormal electroencephalography and a propensity for seizures. In the current study we aimed to assess brain network excitability and seizure propensity in a mouse model of RTT. Mice in which Mecp2 expression was silenced (Mecp2(stop/y)) showed a higher seizure score (mean=6 ± 0.8 compared to 4±0.2 in wild-type [WT]) and more rapid seizure onset (median onset=10 min in Mecp2(stop/y) and 32 min in WT) when challenged with the convulsant drug kainic acid (25mg/kg). Hippocampal slices from Mecp2(stop/y) brain displayed no spontaneous field potential activities under control conditions but showed higher power gamma frequency field potential oscillations compared to WT in response to kainic acid (400 nM) in vitro. Brain slices challenged with the GABA(A)-receptor antagonist bicuculline (0.1-10 μM) and the potassium channel blocker 4-aminopyridine (1-50 μM) also revealed differences between genotypes with hippocampal circuits from Mecp2(stop/y) mouse slices showing enhanced epileptiform burst duration and frequency. In contrast to these network level findings, single cell analysis of pyramidal cells by whole-cell patch clamp recording revealed no detectable differences in synaptic or biophysical properties between methyl-CpG-binding protein 2 (MeCP2)-containing and MeCP2-deficient neurons. These data support the proposal that loss of MeCP2 alters network level excitability in the brain to promote epileptogenesis.