Mutational analysis of the MECP2 gene in Japanese patients with Rett syndrome

Variable predicted pathogenic mechanisms for novel MECP2 variants in RTT patients

BACKGROUND

Methyl CpG binding protein 2 (MeCP2) is essential for the normal function of mature neurons. Mutations in the MECP2 gene are the main cause of Rett syndrome (RTT). Gene mutations have been identified throughout the gene and the mutation effect is mainly correlated with its type and location.

METHODS

In this study, a series of in silico algorithms were applied for analyzing the functional consequences of 3 novel gene missense mutations (D121A, S359Y, and P403S) and a rarely reported one with suspicious effect (R133H) on RettBASE. Besides, a ROC curve analysis was performed to investigate the critical factors affecting variant pathogenicity.

RESULTS

(1) The ROC curve analysis for a retrieved set of MeCP2 variants showed that physicochemical characters do not significantly affect variant pathogenicity; (2) PREM PDI tool revealed that both D121A and R133H mainly contribute to disease progression via reducing MeCP2 affinity to DNA; (3) GPS v5.0 software indicated that P403S may correlate with altered protein phosphorylation; however, no defective protein interaction has been already documented. (4) The applied computational algorithms failed to explore any informative pathogenic mechanism for the S359Y variant.

CONCLUSION

The conducted approach might provide an efficient prediction model for the effect of MECP2 variants that are located in MBD and CTD.

First report of an unusual novel double mutation affecting the transcription repression domain of MeCP2 and causing a severe phenotype of Rett syndrome: Molecular analyses and computational investigation

Rett syndrome is an X-linked neurodevelopmental disorder that develops a profound intellectual and motor disability and affects 1 from 10 000 to 15 000 live female births. This disease is characterized by a period of apparently normal development until 6-18 months of age when motor and communication abilities regress which is caused by mutations occurred in the X-linked MECP2 gene, encoding the methyl-CpG binding protein 2. This research study reports a molecular analysis via an exhaustive gene sequencing which reveals an unusual novel double mutation (c.695 G > T; c.880C > T) located in a highly conserved region in MECP2 gene affecting the transcription repression domain (TRD) of MeCP2 protein and leading for the first time to a severe phenotype of Rett syndrome. Moreover, a computational investigation of MECP2 mutations demonstrates that the novel mutation c.695 G > T is highly deleterious which affects the MeCP2 protein showing also an adverse impact on MECP2 gene expression and resulting in an affected folding and decreased stability of MECP2 structures. Thus, the altered TRD domain engenders a disrupted process of MECP2 functions. Therefore, this is the first study which highlights a novel double mutation among the transcription repression domain (TRD) of MeCP2 protein in Rett patient with a severe clinical phenotype in North Africa region.

Identification of autism-related MECP2 mutations by whole-exome sequencing and functional validation

BACKGROUND

Methyl-CpG-binding protein-2 (MeCP2) is a critical regulator for neural development. Either loss- or gain-of-function leads to severe neurodevelopmental disorders, such as Rett syndrome (RTT) and autism spectrum disorder (ASD). We set out to screen for MECP2 mutations in patients of ASD and determine whether these autism-related mutations may compromise the proper function of MeCP2.

METHODS

Whole-exome sequencing was performed to screen MECP2 and other ASD candidate genes for 120 patients diagnosed with ASD. The parents of patients who were identified with MECP2 mutation were selected for further Sanger sequencing. Each patient accomplished the case report form including general information and clinical scales applied to assess their clinical features. Mouse cortical neurons and HEK-293 cells were cultured and transfected with MeCP2 wild-type (WT) or mutant to examine the function of autism-associated MeCP2 mutants. HEK-293 cells were used to examine the expression of MeCP2 mutant constructs with Western blot. Mouse cortical neurons were used to analyze neurites and axon outgrowth by immunofluorescence experiments.

RESULTS

We identified three missense mutations of MECP2 from three autism patients by whole-exome sequencing: p.P152L (c.455C>T), p.P376S (c.1162C>T), and p.R294X (c.880C>T). Among these mutations, p.P152L and p.R294X were de novo mutations, whereas p.P376S was inherited maternally. The diagnosis of RTT was excluded in all three autism patients. Abnormalities of dendritic and axonal growth were found after autism-related MeCP2 mutants were expressed in mouse cortical neurons; suggesting that autism-related MECP2 mutations impair the proper development of neurons.

CONCLUSIONS

Our study identified genetic mutations of the MECP2 gene in autism patients, which were previously considered to be associated primarily with RTT. This finding suggests that loss-of-function mutations of MECP2 may also lead to autism spectrum disorders.

Identification of autism-related MECP2 mutations by whole-exome sequencing and functional validation

Background

Methyl-CpG-binding protein-2 (MeCP2) is a critical regulator for neural development. Either loss- or gain-of-function leads to severe neurodevelopmental disorders, such as Rett syndrome (RTT) and autism spectrum disorder (ASD). We set out to screen for MECP2 mutations in patients of ASD and determine whether these autism-related mutations may compromise the proper function of MeCP2.

Methods

Whole-exome sequencing was performed to screen MECP2 and other ASD candidate genes for 120 patients diagnosed with ASD. The parents of patients who were identified with MECP2 mutation were selected for further Sanger sequencing. Each patient accomplished the case report form including general information and clinical scales applied to assess their clinical features. Mouse cortical neurons and HEK-293 cells were cultured and transfected with MeCP2 wild-type (WT) or mutant to examine the function of autism-associated MeCP2 mutants. HEK-293 cells were used to examine the expression of MeCP2 mutant constructs with Western blot. Mouse cortical neurons were used to analyze neurites and axon outgrowth by immunofluorescence experiments.

Results

We identified three missense mutations of MECP2 from three autism patients by whole-exome sequencing: p.P152L (c.455C>T), p.P376S (c.1162C>T), and p.R294X (c.880C>T). Among these mutations, p.P152L and p.R294X were de novo mutations, whereas p.P376S was inherited maternally. The diagnosis of RTT was excluded in all three autism patients. Abnormalities of dendritic and axonal growth were found after autism-related MeCP2 mutants were expressed in mouse cortical neurons; suggesting that autism-related MECP2 mutations impair the proper development of neurons.

Conclusions

Our study identified genetic mutations of the MECP2 gene in autism patients, which were previously considered to be associated primarily with RTT. This finding suggests that loss-of-function mutations of MECP2 may also lead to autism spectrum disorders.

Electronic supplementary material

The online version of this article (doi:10.1186/s13229-017-0157-5) contains supplementary material, which is available to authorized users.

RettBASE: Rett syndrome database update

Rett syndrome (RTT) is an X-linked progressive neurodevelopmental disorder that primarily affects females. Mutations in the MECP2 gene have been attributed as the major genetic cause of RTT. Recently, mutations in CDKL5 and FOXG1 genes have also been suggested to give rise to RTT, although subsequent more extensive studies suggest that diseases resulting from mutations in these two genes should be considered as distinct clinical entities. While the genetic basis for the RTT has been recognized, so far there is no effective cure for the disease and the treatments available are mainly aimed at ameliorating clinical problems associated with the disorder. The swift identification of the mutations in children is crucial for pursuing the best therapeutic care. RettBASE was created in 2002 as a MECP2 variant database and has grown to become a comprehensive variant database for RTT and related clinical phenotypes, containing a curated collection of variants for MECP2, CDKL5, and FOXG1 genes. Here, we describe the development and growth of RettBASE after its inception in 2001. Currently, RettBASE holds a total of 4,668 variants in MECP2, 498 variants in CDKL5, and 64 variants in FOXG1.

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.

Intrauterine inflammation, insufficient to induce parturition, still evokes fetal and neonatal brain injury

Exposure to prenatal inflammation is a known risk factor for long term neurobehavioral disorders including cerebral palsy, schizophrenia, and autism. Models of systemic inflammation during pregnancy have demonstrated an association with an immune response an adverse neurobehavioral outcomes for the exposed fetus. Yet, the most common route for an inflammatory exposure to a fetus is from intrauterine inflammation as occurs with chorioamnionitis. The aims of this study were to assess the effect of intrauterine inflammation on fetal and neonatal brain development and to determine if the gestational age of exposure altered the maternal or fetal response to inflammation. CD-1 timed pregnant mice on embryonic day 15 (E15) and E18.5 were utilized for this study. Dams were randomized to receive intrauterine infusion of lipopolysaccharide (LPS, 50 μg/dam) or normal saline. Different experimental groups were used to assess both acute and long-term outcomes. For each gestational age and each treatment group, fetal brains, amniotic fluid, maternal serum and placentas were collected 6h after intrauterine infusion. Rates of preterm birth, maternal morbidity and litter size were assessed. IL6 levels were assayed in maternal serum and amniotic fluid. An immune response was determined in the fetal brains and placentas by QPCR. Cortical cultures were performed to assess for fetal neuronal injury. Gene expression changes in postnatal day 7 brains from exposed and unexposed pups were determined. In the preterm period, low dose LPS resulted in a 30% preterm birth rate. Litter sizes were not different between the groups at either gestational age. IL6 levels were not significantly increased in maternal serum at either gestational time period. Low dose LPS increased IL6 levels in the amniotic fluid from exposed dams in the term but not preterm period. Regardless of gestational age of exposure, low dose intrauterine LPS activated an immune response in the placenta and fetal brain. Exposure to intrauterine LPS significantly decreased dendritic counts in cortical cultures from both the preterm and term period. Exposure to intrauterine inflammation altered gene expression patterns in the postnatal brain; this effect was dependent on gestational age of exposure. In conclusion, intrauterine inflammation, even in the absence of preterm parturition, can evoke fetal brain injury as evidence by alterations in cytokine expression and neuronal injury. Despite an absent or limited maternal immune response in low dose intrauterine inflammation, the immune system in the placenta is activated which is likely sufficient to induce a fetal immune response and subsequent brain injury. Changes in the fetal brain lead to changes in gene expression patterns into the neonatal period. Subclinical intrauterine inflammation can lead to fetal brain injury and is likely to be mechanistically associated with long term adverse outcomes for exposed offspring.

Homozygosity for MECP2 gene in a girl with classical Rett syndrome

We report a 21 year-old girl with classical Rett syndrome (RS) based on clinical diagnosis. The molecular testing of MECP2 gene revealed that the patient is homozygous for a de novo 473C > T mutation, causing the T158M amino acid change. Chromosome analysis showed a normal karyotype, and the haplotype analysis ruled out the possibility of parental disomy or microdeletion in MECP2 gene. Cultured fibroblast analysis reveals a mosaic for the mutation. This is a documented case of a homozygous female with RS.

MECP2 coding sequence and 3'UTR variation in 172 unrelated autistic patients

Mutations in the coding sequence of the methyl-CpG-binding protein 2 gene (MECP2), which cause Rett syndrome (RTT), have been found in male and female autistic subjects without, however, a causal relation having unequivocally been established. In this study, the MECP2 gene was scanned in a Portuguese autistic population, hypothesizing that the phenotypic spectrum of mutations extends beyond the traditional diagnosis of RTT and X-linked mental retardation, leading to a non-lethal phenotype in male autistic patients. The coding region, exon-intron boundaries, and the whole 3'UTR were scanned in 172 patients and 143 controls, by Detection of Virtually All Mutations-SSCP (DOVAM-S). Exon 1 was sequenced in 103 patients. We report 15 novel variants, not found in controls: one missense, two intronic, and 12 in the 3'UTR (seven in conserved nucleotides). The novel missense change, c.617G > C (p.G206A), was present in one autistic male with severe mental retardation and absence of language, and segregates in his maternal family. This change is located in a highly conserved residue within a region involved in an alternative transcriptional repression pathway, and likely alters the secondary structure of the MeCP2 protein. It is therefore plausible that it leads to a functional modification of MeCP2. MECP2 mRNA levels measured in four patients with 3'UTR conserved changes were below the control range, suggesting an alteration in the stability of the transcripts. Our results suggest that MECP2 can play a role in autism etiology, although very rarely, supporting the notion that MECP2 mutations underlie several neurodevelopmental disorders.

Low significance of MECP2 mutations as a cause of mental retardation in Brazilian males

MeCP2 is a protein that selectively binds to methylated cytosines through its methyl-CpG-binding domain (MBD) and connects DNA methylation to transcriptional repression. Mutations in MECP2 gene, located in Xq28, have been reported as being the major cause of Rett syndrome and are also associated with some cases of X-linked mental retardation in both males and females. In this study, we present the first screening in the MECP2 gene in a Brazilian cohort of 239 unrelated males with idiopathic mental retardation. Eight sequence variations were observed in 10 patients: one novel putative pathogenic variant, two never described variants of unknown pathogenic value and five non-pathogenic variations. We conclude that in mentally retarded Brazilian males, non-pathogenic variants in the MECP2 gene are more common than actual pathogenic mutations, and therefore alterations in this gene have a weak relationship with mental retardation in males.

Rett syndrome: clinical and molecular characterization of two Brazilian patients

BACKGROUND: Rett syndrome (RS) is recognized as a pan-ethnic condition. Since the identification of mutations in the MECP2 gene, more patients have been diagnosed, and a broad spectrum of phenotypes has been reported. There is a lack of phenotype-genotype studies. OBJECTIVE: To describe two cases of Brazilian patients with identified MECP2 mutations. METHOD: We present two female Brazilian patients with RS. RESULTS: Both patients presented with regression at 2-3 years of age, when stereotypic hand movements, social withdrawal and postnatal deceleration of head growth rate were observed. Both patients presented verbal communication impairment. Case 1 had loss of purposeful hand movements, and severe seizure episodes. Case 2 had milder impairment of purposeful hand movements, and no seizures. They had different mutations, D97Y and R294X, found in exons 3 and 4 of MECP2 gene, respectively. CONCLUSION: Testing for MECP2 mutations is important to confirm diagnosis and to establish genotype/phenotype correlations, and improve genetic counseling.

Comprehensive diagnosis of Rett's syndrome relying on genetic, epigenetic and expression evidence of deficiency of the methyl-CpG-binding protein 2 gene: study of a cohort of Israeli patients

BACKGROUND

Despite advances in the characterisation of mutations in the MECP2-coding region, a small proportion of classic RTT cases remain without recognisable mutations.

OBJECTIVE AND METHODS

To identify previously unknown mutations, a quantitative assay was established, providing estimates of MECP2_e1 and MECP2_e2 expression levels in peripheral blood. A systematic analysis of an Israeli cohort of 82 patients with classic and atypical RTT is presented, including sequence analysis of the MECP2-coding region, MLPA, XCI and quantitative expression assays.

RESULTS AND CONCLUSION

A novel mis-sense mutation at ca 453C-->T (pD151E), resulting in a change of a conserved residue at the methyl-binding domain, and a rare GT deletion of intron 1 donor splice site are reported. It is shown that various MECP2 mutations had distinct effects on MECP2 expression levels in peripheral blood. The most significant (p<0.001) reduction in the expression of both MECP2 isoforms was related to the presence of the intron 1 donor splice-site mutation. Using quantitative expression assays, it was shown that several patients with classic and atypical RTT with no mutation findings had significantly lower MECP2 expression levels. Further research on these patients may disclose still elusive non-coding regulatory MECP2 mutations.

MECP2 and CDKL5 gene mutation analysis in Chinese patients with Rett syndrome

Rett syndrome (RTT) is a progressive neurodevelopmental disorder that is caused by mutations in the X-linked methyl-CpG-binding protein2 (MECP2) gene. In this study, the MECP2 sequences in 121 unrelated Chinese patients with classical or atypical RTT were screened for deletions and mutations. In all, we identified 45 different MECP2 mutations in 102 of these RTT patients. The p. T158M mutation (15.7%) was the most common, followed in order of frequency by p. R168X (11.8%), p. R133C (6.9%), p. R270X (6.9%), p. G269fs (6.9%), p. R255X (4.9%), and p. R306C (3.9%). In addition, we identified five novel MECP2 mutations: three missense (p. K305E, p. V122M, p. A358T), one insertion (c.45-46insGGAGGA), and one 22 bp deletion (c.881-902del22). Large deletions represented 10.5% of all identified MECP2 mutations. Conversely, mutations in exon 1 appeared to be rare (0.9%). The remaining cases without MECP2 mutations were screened for the cyclin-dependent kinase-like 5 (CDKL5) gene using denaturing high-performance liquid chromatography (DHPLC). One synonymous mutation (p. I72I) was found in exon 5, suggesting that CDKL5 is a rare cause of RTT. The overall MECP2 mutation detection rate for this patient series was 84.3:87.9% in 107 classical RTT cases and 57.1% in 14 atypical RTT cases. Moreover, there were two patients with homozygous mutations and normal female karyotypes. However, we did not pinpoint a significant relationship between genotype and phenotype in these cases.

Management of a severe forceful breather with Rett syndrome using carbogen

We have used a novel neurophysiological technique in the NeuroScope system in combination with conventional electroencephalography (EEG) to monitor both brainstem and cortical activity simultaneously in real-time in a girl with Rett syndrome. The presenting clinical features in our patient were severe sleep disturbances, irregular breathing in the awake state dominated by Valsalva's type of breathing followed by tachypnoea and very frequent attacks of seizures and vacant spells. Our novel neurophysiological data showed that the patient was a Forceful Breather according to the breathing categories in Rett syndrome. She had frequent abnormal spontaneous brainstem activation (ASBA) preceded by severe attacks of hypocapnoea, which was caused by a combination of Valsalva's type of breathing and tachypnoea and all these together were responsible for the seizures and non-epileptic vacant spells. The ASBA was not detectable in conventional EEG and there were no epileptiform changes in the EEG during the seizures and vacant spells caused by the hypocapnic attacks, therefore these were pseudo-seizures. The record of brainstem activity confirmed that these were autonomic events, a kind of "brainstem epilepsy". We successfully treated the sleep disturbance with Pipamperone, a 5-hydroxytryptophan antagonist of receptor type 2 and we prevented the severe hypocapnoea during Valsalva's type of breathing and during tachypnoea using carbogen (a mixture of 5% carbon dioxide and 95% oxygen), which we gave by inhalation. Our treatment drastically reduced the autonomic events, promoted whole night sleep and significantly improved the quality of life in our patient. She can now participate in normal family activity which was previously impossible before treatment.

Widened clinical spectrum of the Q128P MECP2 mutation in Rett syndrome

CASE REPORT

We describe a female patient with Arnold Chiari type I malformation, atypical Rett syndrome characterized by postnatal onset microcephaly, stereotypic hand movements, ataxia, severe developmental delay, intractable tonic-clonic seizures, and a MECP2 mutation with a unique set of clinical findings. Implementation of a ketogenic diet resulted in decreased seizure activity and an improvement in the patient's degree of social relatedness with her family members.

DISCUSSION

An early diagnosis of Rett syndrome allows families to maximize utilization of existing treatment modalities and seek appropriate genetic counseling and prenatal diagnoses. This case also provides further evidence for the treatment benefit of ketogenic diets for seizures in patients with Rett syndrome.

Early motor disturbances in Rett syndrome and its pathophysiological importance

Assessment of the development of motor function of Rett syndrome (RTT) revealed hypotonia with failure of crawling and disturbance in skillful hand manipulation are shown as early motor signs. Clinical evaluation has revealed the former as postural hypotonia with failure in locomotion and neurophysiological examinations have showed this to be due to hypofunction of the aminergic neurons of the brainstem. The latter signs are considered to indicate dysfunction of the corticospinal tract at higher levels. As the signs appear along with deceleration of head growth, dysfunction of the noradrenergic neuron, which is involved in synaptogenesis in the cerebral cortex, is postulated as the cause. The characteristic stereotyped hand movements appear in early childhood after loss of purposeful hand use and are underlain by rigid hypertonus. Neurophysiological examinations have indicated that these are due to hypofunction of the nigrostriatal (NS) dopamine (DA) neuron. By comparison with animal experimental work the neurohistochemical changes in the substantia nigra of the autopsied brain of RTT suggest a lesion caused by the dysfunction of the pedunculopontine nucleus, induced by dysfunction of the brainstem aminergic neurons which modulate postural tone and locomotion. Hypofunction of the aminergic neurons also cause 'leakage' of atonia into non-REM stages which lead to disturbances in the autonomic nervous system through inhibition of the reflex system. The grade of disturbance of locomotion closely matches the grade in abnormalities of higher cortical function as indicated by the development of meaningful words. The loci of missense mutation of methyl CPG binding domain of MECP 2gene which affect locomotion severely also markedly impaired their effects on the formation of the heterochromatin. Thus, dysfunction of the aminergic neurons of the brainstem which regulate postural tone and locomotion is proposed as the primary lesion.

Does genotype predict phenotype in Rett syndrome?

Mutations in the X-linked gene encoding the methyl-CpG binding protein MeCP2 are the primary cause of classic and atypical Rett syndrome and have recently been shown to contribute to other neurodevelopmental disorders of varying severity. To determine whether there are molecular correlates to the phenotypic heterogeneity, numerous groups have performed genotype-phenotype correlation studies. These studies have yielded conflicting results, in part because they used different criteria for determining severity and classifying mutations. Evolution of the phenotype with age and variable expressivity arising from individual variability in X-chromosome inactivation patterns are among other reasons the findings varied. Nonetheless, evidence of differences in the phenotypic consequences of specific types of mutations is emerging. This review analyzes the available literature and makes recommendations for future studies.

Histone modifications in Rett syndrome lymphocytes: a preliminary evaluation

Most cases of Rett syndrome (RTT) are associated with mutations in the coding region of the transcriptional regulator MeCP2. This gene appears to repress gene expression through chromatin conformational changes secondary to histone modifications, mainly histone deacetylation of core histones H3 and H4. There is limited and contradictory information about histone modifications in RTT tissues. The present study intended to provide a preliminary characterization of histone acetylation (AcH3, AcH4) and methylation (MeH3) in RTT, with emphasis on non-selected peripheral cells and molecular-neurologic correlations. We compared 17 females with RTT, 11 of them with MeCP2 mutations, with 10 gender-matched controls in terms of lymphocyte lysate immunoblotting-based levels. We found that immunoreactivities for MeCP2 and AcH3/AcH4 are variable in both control and RTT subjects. Despite this variability, RTT subjects with nonsense mutations showed the expected reduction in C-terminal MeCP2 immunoreactivity. Regardless of MeCP2 levels, both subjects with (RTTPos) and without (RTTNeg) mutations had decreased levels of AcH3. The latter reductions were mainly driven by decreases in levels of H3 acetylated at lysine residue 14 (AcH3K14) and independent of parallel, but milder, decreases in immunoreactivity for MeH3 lysine residues (MeH3K4/MeH3K9). Within our study sample, reductions in AcH3 were correlated with severity of head growth deceleration in the RTTPos group. This contrasted with the lack of significant association between location of MeCP2 mutation and severity of the RTT neurologic phenotype. We concluded that there were distinctive profiles of histone acetylation/methylation in RTT peripheral cells, which reflect pathogenetic mechanisms common to subjects with clinical features of this disorder, regardless of mutation status, and that these patterns may be relevant to neurologic dysfunction in RTT.

Methyl-CpG binding protein 2 gene (MECP2) variations in Japanese patients with Rett syndrome: pathological mutations and polymorphisms

A total of 45 different mutations of methyl-CpG-binding protein 2 gene (MECP2) were identified in 145 of 219 Japanese patients with typical or atypical Rett syndrome (RTT) (66.2%). A missense mutation, T158M was the most common mutation of MECP2, identified in 22 (19.1%) patients, followed by four nonsense mutations, R168X (14.8%), R270X (13.0%), R255X (9.6%), and R294X (6.1%) in 115 patients with classical RTT. Two missense mutations, R133C (33.3%) and R306C (23.3%), and a nonsense mutation, R294X (13.3%), were common in 30 patients with atypical RTT, including the preserved speech variant (PSV). Frameshift mutations due to nucleotide deletion or insertion were identified in 22 patients with MECP2 mutations, and one of them had a 3.6 kb deletion encompassing exons 3 and 4. Three patients with classical RTT had a splicing anomaly. The wide spectrum of phenotypic variability in patients with RTT has been considered to be correlated with the mutation type and location in MECP2, and X-inactivation. However, most patients showed a random X-inactivation pattern evaluated by an androgen receptor gene polymorphism in this study, suggesting that a skewed X-inactivation might not be a main modification factor on clinical phenotypes of RTT. In addition, three new missense mutations, P176R, A378V and T479M, were identified in patients with RTT, but also in healthy Japanese, indicating that these mutations are non-pathogenic in Japanese. Information about rare polymorphic variations is very important for the molecular diagnosis of RTT, although rare polymorphic variants might differ among ethnic groups.

MECP2mutation analysis in patients with mental retardation

Mutations in the methyl-CpG-binding protein 2 (MECP2) gene are known to underlie Rett' syndrome, the most common cause of mental retardation (MR) in girls. Since the original report, phenotypes resulting from MECP2 mutations have been shown to extend, for example, to several Rett variants, autism, atypical Angelman syndrome, and nonspecific MR. It was earlier proposed that MECP2 mutations might account for approximately 2% of the male cases with nonspecific MR. Thereby, the frequency of MECP2 mutations in the mentally retarded population would be comparable to that of Fragile-X syndrome. The aim of this study was to analyze well-characterized cases with MR and to clarify the role of the MECP2 gene in the etiology of MR and atypical Angelman syndrome. The coding sequence of the MECP2 gene was analyzed in a sample of 118 patients (103 males, 15 females) by direct sequencing. Two coding sequence variants, 602C > T (A201V) and 1189G > A (E397K), were identified. In addition, we identified four variants in the intronic or 3'UTR regions. None of these variants is likely to be causal. We conclude that the evidence across all the mutation screening studies implies that MECP2 mutations do not represent a major cause of nonspecific MR.

Mild overexpression of MeCP2 causes a progressive neurological disorder in mice

Mutations in the X-linked methyl-CpG-binding protein 2 (MECP2), encoding a transcriptional repressor, cause Rett syndrome and a variety of related neurodevelopmental disorders. The vast majority of mutations associated with human disease are loss-of-function mutations, but precisely what aspect of MeCP2 function is responsible for these phenotypes remains unknown. We overexpressed wild-type human protein in transgenic mice using a large genomic clone containing the entire human MECP2 locus. Detailed neurobehavioral and electrophysiological studies in transgenic line MeCP2(Tg1), which expresses MeCP2 at approximately 2-fold wild-type levels, demonstrated onset of phenotypes around 10 weeks of age. Surprisingly, these mice displayed enhanced motor and contextual learning and enhanced synaptic plasticity in the hippocampus. After 20 weeks of age, however, these mice developed seizures, became hypoactive and approximately 30% of them died by 1 year of age. These data demonstrate that MeCP2 levels must be tightly regulated in vivo, and that even mild overexpression of this protein is detrimental. Furthermore, these results support the possibility that duplications or gain-of-function mutations in MECP2 might underlie some cases of X-linked delayed-onset neurobehavioral disorders.

Influence of MECP2 gene mutation and X-chromosome inactivation on the Rett syndrome phenotype

To date, approximately 200 different mutations in the MECP2 gene have been identified. We analyzed the entire coding sequence of the MECP2 gene and the X-chromosome inactivation pattern in 42 sporadic cases of Rett syndrome. Of the 42 patients, 30 had pathogenic mutations, including 14 different mutations: 9 missense mutations, 4 nonsense mutations, and 1 frameshift mutation. One was a novel mutation (S134P). There was a tendency for patients who had a nonsense mutation in the transcriptional repression domain region to show earlier onset of regression and more severe language retardation than patients with a mutation in the methyl-CpG binding domain region. However, the parameters of clinical severity were variable among patients with the same type of mutation, depending on the pattern of X-chromosome inactivation. This study suggests that the X-chromosome inactivation pattern can modify the phenotype of Rett syndrome, which is primarily determined by the type and site of MECP2 gene mutation.

Trisomy 21 and Rett syndrome: a double burden

Rett syndrome is a severe neurodevelopmental disorder generally affecting girls. Affected individuals are apparently normal at birth but later pass through a period of regression with loss of hand and communication skills and the development of hand stereotypies and dyspraxia. Mutations in the methyl-CpG binding protein 2 (MECP2) gene, have now been found to cause Rett syndrome in up to 80% of classical cases. We report a girl with Down syndrome, one of three children with birth defects in a family of five. From the age of 18 months she developed symptomatology considered by her primary physician to be very characteristic of Rett syndrome. However, this remained a clinical diagnosis till the age of 12 years. Laboratory confirmation of the dual diagnosis, which includes a R168X mutation in the MECP2 gene in addition to trisomy 21, has now been possible. The presence of one neurological or developmental disorder does not necessarily preclude a diagnosis of Rett syndrome.

Phenotypic manifestations of MECP2 mutations in classical and atypical Rett syndrome

Since the identification of mutations in MECP2 in girls and women with apparent Rett syndrome, numerous efforts have been made to develop phenotype-genotype correlations. These studies have produced conflicting results in part related to use of different clinical severity scales, different diagnostic criteria, and different stratification by age and mutation group as well as the possible effects of unbalanced X-chromosome inactivation. The present study applied a revised ordinal scoring system that allowed for correction for patient ages. We analyzed 85 patients with mutation in MECP2. Sixty-five (76%) had one of eight common mutations. Patients with missense mutations had lower total severity scores and better language performance than those with nonsense mutations. No difference was noted between severity scores for mutations in the methyl-binding domain (MBD) and the transcriptional repression domain (TRD). However, patients with missense mutations in TRD had the best overall scores and better preservation of head growth and language skills. Analysis of specific mutation groups demonstrated a striking difference for patients with the R306C mutation including better overall score, later regression, and better language with less motoric impairment. Indeed, these patients as a group accounted for the differences in overall scores between the missense and nonsense groups. Thus, the impact of specific mutations coupled with possible variation in X-chromosome inactivation must be considered carefully in the derivation of phenotype-genotype correlations. These results emphasize the limitations of such analyses in larger mutation groups, either by type or position.

The spectrum of phenotypes in females with Rett Syndrome

Since the discovery of mutations in the methyl-CpG binding protein-2 (MECP2) gene in Rett Syndrome (RTT) a large number of females have been diagnosed worldwide. In this article we present the clinical and developmental data of 120 RTT females with mutations in the MECP2 gene and individually describe typical and atypical cases. We found a broad spectrum of phenotypes in females. At the severest end we have females with primary developmental delay who never learned to turn, sit or walk and who developed severe epilepsy. At the mildest end of the spectrum, there are females with only minor neurological symptoms who have good gross motor function, speak and have relatively well-preserved hand function. A number of girls either do not fulfil all the necessary diagnostic criteria or present with symptoms that have not been described in RTT before. Comparing our data with the normal population we found that girls with RTT have a smaller occipito-frontal circumference, shorter length and lower weight at birth. As a result of molecular genetic analysis a broad spectrum of phenotypes in RTT females has evolved. We found evidence that the defect in MeCP2 influences the somatic growth before birth.

Mutations and polymorphisms in the human methyl CpG-binding protein MECP2

Rett syndrome (RTT or RS) is a neurodevelopmental disorder and one of the most frequent genetic diseases in girls. Mutations of the MECP2 gene have been found in a variety of different RTT phenotypes. The MECP2 gene (Xq28) has been described in 1992. Up to now, 218 different mutations have been reported in a total group, of more than 2,100 patients. Mutations in the MECP2 gene are responsible for up to 75% of the classical RTT cases. The mutations, are distributed along the whole gene and are comprised of all types of mutations. Several polymorphisms and benign genetic variants have also been described. Apart from spared reported familial cases, almost all cases are sporadic. RTT syndrome has been considered to be a lethal trait in males. Studying the parental origin of the mutations, however, we and others have found a very high prevalence of de novo mutations on the paternal chromosome. In this work we summarize the mutational reports published until now. One of our aims was to check the mutations' descriptions for consistency and particularly to rename them according to the recommended mutation nomenclature. The increasing number of investigations on the functions of the MeCP2 can help to gain more information about the neuropathogenetic mechanisms causing RTT. Hum Mutat 22:107-115, 2003.

Effects of MECP2 mutation type, location and X-inactivation in modulating Rett syndrome phenotype

Rett syndrome (RTT) is a clinically defined disorder that describes a subset of patients with mutations in the X-linked MECP2 gene. However, there is a high degree of variability in the clinical phenotypes produced by mutations in MECP2, even amongst classical RTT patients. In a large-scale screening project, this variability has been examined by looking at the effects of mutation type, functional domain affected and X-inactivation. Mutations have been identified in 60% of RTT patients in this study (25% of whom were atypical), including 23 novel mutations and polymorphisms. More mutations were found in classical patients (63%) compared to atypical patients (44%). All of the pathogenic mutations were de novo in patients for whom parent DNA was available for screening. A composite phenotype score was developed, based on the recommendations for reporting clinical features in RTT of an international collaborative group. This score proved useful for summarising phenotypic severity, but did not correlate with mutation type, domain affected or X-inactivation, probably due to complex interactions between all three. Other correlations suggested that truncating mutations and mutations affecting the methyl-CpG-binding domain tend to lead to a more severe phenotype. Skewed X-inactivation was found in a large proportion (43%) of our patients, particularly in those with truncating mutations and mutations affecting the MBD. It is therefore likely that X-inactivation does modulate the phenotype in RTT.

Identification of MeCP2 mutations in a series of females with autistic disorder

Rett disorder and autistic disorder are both pervasive developmental disorders. Recent studies indicate that at least 80% of Rett Disorder cases are caused by mutations in the methyl-CpG-binding protein 2 (MeCP2) gene. Since there is some phenotypic overlap between autistic disorder and Rett disorder, we analyzed 69 females clinically diagnosed with autistic disorder for the presence of mutations in the MeCP2 gene. Two autistic disorder females were found to have de novo mutations in the MeCP2 gene. These data provide additional evidence of variable expression in the Rett disorder phenotype and suggest MeCP2 testing may be warranted for females presenting with autistic disorder.

Describing the phenotype in Rett syndrome using a population database

BACKGROUND

Mutations in the MECP2 gene have been recently identified as the cause of Rett syndrome, prompting research into genotype-phenotype relations. However, despite these genetic advances there has been little descriptive epidemiology of the full range of phenotypes.

AIMS

To describe the variation in phenotype in Rett syndrome using four different scales, by means of a population database.

METHODS

Using multiple sources of ascertainment including the Australian Paediatric Surveillance Unit, the development of an Australian cohort of Rett syndrome cases born since 1976 has provided the first genetically characterised population based study of Rett syndrome. Follow up questionnaires were administered in 2000 to families and used to provide responses for items in four different severity scales.

RESULTS

A total of 199 verified cases of Rett syndrome were reported between January 1993 and July 2000; 152 families provided information for the follow up study. The mean score using the Kerr scale was 22.9 (SD 4.8) and ranged from 20.5 in those under 7 years to 24.2 in those over 17 years. The mean Percy score was 24.9 (SD 6.6) and also increased with age group from 23.0 to 26.9. The mean Pineda score was 16.3 (SD 4.5) and did not differ by age group. The mean WeeFIM was 29.0 (SD 11.9), indicating extreme dependence, and ranged from 18 to 75.

CONCLUSION

We have expanded on the descriptive epidemiology of Rett syndrome and shown different patterns according to the severity scale selected. Although all affected children are severely functionally dependent, it is still possible to identify some variation in ability, even in children with identified MECP2 mutations.

Rett syndrome: investigation of nine patients, including PET scan

BACKGROUND

We describe nine females with Rett Syndrome (RS), aged 14 to 26 years. All had had developmental delay before the end of their first year and had subsequently regressed to profound dementia with apraxia, ataxia, irregular respirations and often also seizures.

METHODS

The Revised Gesell developmental assessment and Alpern-Boll Developmental Profile were used in modified form. Volumetric measurements of basal ganglia using MRI were compared with the findings in nine age-matched volunteer females. Positron emission scans with [18F]-6-fluorodopa and [11C]-raclopride were performed under light anesthesia with intravenous Propofol, and the findings were compared with those in healthy control girls. Bidirectional sequencing of the coding regions of the MECP2 gene was investigated in blood samples for mutational analyses.

RESULTS

The RS females functioned at a mental age level ranging from about 4 to 15 months. The scores correlated with height, weight and head circumference. Magnetic resonance scans of basal ganglia showed a significant reduction in the size of the caudate heads and thalami in the Rett cases. Positron emission scans demonstrated that the mean uptake of fluorodopa in RS was reduced by 13.1% in caudate and by 12.5% in putamen as compared to the controls, while dopamine D2 receptor binding was increased significantly by 9.7% in caudate and 9.6% in putamen. Mutations in the coding regions of the MECP2 gene were present in all nine patients. No significant correlation between type and location of mutation and volumetric changes or isotope uptake was demonstrable.

CONCLUSIONS

Our findings suggest a mild presynaptic deficit of nigrostriatal activity in Rett syndrome.

Rett syndrome. Current status and new vistas

RS, the most common cause of profound cognitive impairment in girls and women, is composed of characteristic clinical features, including communication dysfunction, stereotypic movements, and pervasive growth failure. Neuropathologic findings indicate a failure of neuronal maturation with too small neurons and too few dendritic arbors and no evidence of a progressive neurodegenerative process. The combination of clinical and neuropathologic characteristics presents the profile of a neurodevelopmental disorder. Mutations in the gene MECP2, which encodes MeCP2, have been identified in 80% to 85% of girls and women with RS. Furthermore, the panorama of phenotypes with MECP2 mutations now extends far beyond RS to include normal girls and women, mild learning disability, autistic spectrum disorders, and X-linked mental retardation. These rapid advances in our understanding of RS over the past three decades have opened new avenues of study in developmental neurobiology.

Genetic basis of Rett syndrome

The origin of Rett syndrome has long been debated, but several observations have suggested an X-linked dominant inheritance pattern. We and others have pursued an exclusion-mapping strategy using DNA from a small number of familial Rett syndrome cases. This work resulted in the narrowing of the region likely to harbor the mutated gene to Xq27.3-Xqter. After systematic exclusion of several candidate genes, we discovered mutations in MECP2, the gene that encodes the transcriptional repressor, methyl-CpG-binding protein 2. Since then, nonsense, missense, or frameshift mutations have been found in at least 80% of girls affected with classic Rett syndrome. Sixty-four percent of mutations are recurrent C > T transitions at eight CpG dinucleotides mutation hotspots, while the C-terminal region of the gene is prone to recurrent multinucleotide deletions (11%). Most mutations are predicted to result in total or partial loss of function of MeCP2. There is no clear correlation between the type and position of the mutation and the phenotypic features of classic and variant Rett syndrome patients, and XCI appears to be a major determinant of phenotypic severity. Further research focuses on the pathogenic consequences of these mutations along the hypothesis of loss of transcriptional repression of a small number of genes that are essential for neuronal function in the maturing brain.

Associations between MeCP2 mutations, X-chromosome inactivation, and phenotype

Rett syndrome is a neurodevelopmental disorder of early postnatal brain growth in girls. Patients show a normal neonatal period with subsequent developmental regression and a loss of acquired skills (communication and motor skills), deceleration of head growth, and development of typical hand stereotypies. Recent studies have shown that mutations in the X-linked methyl CpG binding protein 2 gene (MeCP2) cause most typical cases of Rett syndrome. The MeCP2 gene encodes a protein that binds methylated cytosine residues of CpG dinucleotides and mediates, with histone deacetylases and transcriptional repressors, the transcription "silencing" of other genes. Girls with Rett syndrome exhibit mosaic expression for the MeCP2 defect at the cellular level, with most patients showing random X-inactivation and approximately equal numbers of cells expressing the normal MeCP2 gene and the mutated MeCP2 gene. In rare cases, females with a MeCP2 mutation escape phenotypic expression of the disorder because of nonrandom X-inactivation and the preferential inactivation of the mutated MeCP2 allele. Nonrandom patterns of X-inactivation may also contribute to the clinical variability often seen in girls with Rett syndrome. The spectrum of clinical phenotype caused by MeCP2 mutations is wide, including milder "preserved speech" variants, the severe congenital Rett variant, and a subset of X-linked recessive mental retardation in boys. Studies have shown that atypical and classical Rett syndrome can caused by the same MeCP2 mutations, indicating clinical phenotype is variable even among girls with the same MeCP2 mutation. The relationship between type of MeCP2 mutation, X-inactivation status, and clinical phenotype of Rett syndrome is complex and likely involves other environmental and polygenic modifiers.

Clinical trials and treatment prospects

Prospects for definitive therapeutic intervention for Rett syndrome (RS) have been elevated by the discovery of mutations in the methyl-CpG-binding protein 2 gene (MECP2) in more than 80% of females meeting clinical criteria for this disorder. As such, a review of previous clinical trials, descriptions of the status of clinical management for the prominent medical problems of RS, and a preview of an ongoing clinical trial conducted jointly at the Baylor College of Medicine and the University of Alabama at Birmingham are presented. The conduct of controlled clinical trials requires adherence to diagnostic criteria for RS; stratification by age, stage, and presence of MECP2 mutations; and use of clearly defined outcome measures. Previous clinical trials in RS have been conducted with L-carnitine, the ketogenic diet, and the opiate antagonist, naltrexone. The L-carnitine and naltrexone trials were double blind, placebo-controlled and us ed the motor behavioral analysis described in this review. All failed to provide evidence of dramatic improvements in the clinical features of RS. Specific recommendations are presented for clinical management of growth failure, breathing irregularities, seizures, ambulation, scoliosis, gastrointestinal function, self abuse, and habilitation/education although systematic evaluations of each in the context of RS have not been conducted. The only ongoing trial involves dietary supplementation with folate and betaine and is based on the finding that gene expression of some alleles of the agouti gene could be altered by dietary methyl supplementation. The availability of animal models expressing mutations in MECP2 should enhance the evaluation of innovative therapies for RS.

Annotation: Rett syndrome: recent progress and implications for research and clinical practice

BACKGROUND

Rett syndrome was first described 40 years ago as a profoundly disabling condition in girls.

METHOD

Over the last 20 years' national surveys, neuropathological and neurophysiological research have steadily improved understanding of its character and natural history.

RESULTS

In the last two years identification of the causative mutations in the gene methyl CpG binding protein 2 (Xq28) has led to a sudden expansion in knowledge about the underlying developmental disorder, with important implications for clinical practice and new opportunities to develop more effective intervention.

CONCLUSIONS

It is now clear that the disorder occurs in males and females and that there is a wide range in severity.

Mutation analysis of MECP2 and clinical characterization in Korean patients with Rett syndrome

Rett syndrome is a progressive neurodevelopmental disorder occurring predominantly in females. Recently, mutations in the MECP2 gene on Xq28, which encodes methyl-CpG binding protein 2, were identified as responsible for some cases of Rett syndrome. In the present study, we analyzed the entire coding sequence of the MECP2 gene in 20 sporadic cases of Rett syndrome in Korea. Of the 20 patients, 14 (70%) had pathogenic mutations, which included 10 different mutations. Altogether, there were five missense mutations (D97Y, L100V, R133C, T158M, R306C), four nonsense mutations (R168X, R255X, R270X, R294X), and one frameshift mutation (a 41-bp deletion at 1157-1197). Two of these were novel mutations (D97Y, L100V). Most of the nucleotide substitutions involved C to T transitions at CpG hotspots. We could find no clear phenotype-genotype correlation according to the type of mutation. However, there was a tendency for patients with no MECP2 mutation (30%) to show more severe symptoms and more rapid clinical progression than patients with mutations. Further studies are necessary to identify the other possible genetic causes of Rett syndrome.

Rett syndrome: clinical manifestations in males with MECP2 mutations

Rett syndrome is a neurodevelopmental disorder characterized by cognitive and adaptive regression with autistic features, loss of acquired skills, and stereotypic hand movements that almost exclusively affects females. It is an X-linked dominant disorder, with presumed lethality in males. Nonetheless, there are a few descriptions of males suspected of having Rett syndrome. With the recent discovery that the MECP2 gene is responsible for most cases of Rett syndrome, it is possible to molecularly assess cases of affected males by direct sequencing analysis. We describe an Israeli family consisting of a female having classic Rett syndrome and a male sibling with severe neonatal encephalopathy. Molecular analysis revealed that both sister and brother have the same MECP2 gene mutation; however, their mother does not. This case, as well as other published studies of males with MECP2 mutations, reveals that the clinical manifestations in viable males vary from neonates with severe encephalopathy to adults with mental retardation and demonstrate genotype-phenotype correlations.

Discussant--pathophysiologies of Rett syndrome

Studies on sleep parameters of Rett syndrome revealed hypoactivity of the noradrenaline (NA) and the serotonin (5HT) neuron in early infancy while preserving the function of the dopamine (DA) and the cholinergic neurons of the pons normally. The sleep-wake cycle remains in its development at the level of 4 months of age. Polysomnographies also showed a decrease of the function of the nigrostriatal (NS)-DA neuron in early childhood and suggested the development of receptor supersensitivity in late childhood. Neurohistochemical and neuroimaging (PET) studies revealed the hypofunction of the NS-DA neuron with receptor supersensitivity and of involvement of the cholinergic neurons to the cortical pathology, whereas no substantial pathological or histochemical abnormalities were observed in the NA and the 5HT neurons in the brainstem. The decrease of tyrosine hydroxylase without neurodegenerative changes observed in the substantia nigra of Rett syndrome had similarity to the pathology caused by excitotoxic lesion of the pedunculopontine nuclei (PPN) observed in an animal experiments. Clinically the grade of disability of locomotion was shown to correlate to the grade of the disabilities of language. These clinical manifestations were also correlated to the specific loci of the mutation in the methyl binding domain of the MECP2 gene. In rodents the axons of the brainstem 5HT neuron involved in the morphogenesis of the brain in the early developmental course disappear in neonates without apoptotic or degenerative changes in the neurons. This period corresponds to the first 1.5-2 years in humans. Thus, in Rett syndrome, the primary lesion appears in the brainstem NA and 5HT neurons which affects development of synaptogenesis of the cortex and also dysfunction of the PPN. The latter causes dysfunction of the DA neuron and the cholinergic neuron in the midbrain. The mutation of the MECP2 gene may cause early transcription of the genes which prune the axons of the aminergic neurons for the developmental morphogenesis of the central nervous system in early infancy.

Spectrum of MECP2 mutations in Rett syndrome

Mutations in the methyl-CpG-binding protein 2 gene (MECP2) are identified in the majority of females with Rett syndrome (RTT), an X-linked dominant neurodevelopmental disorder. We searched for mutations by sequencing the MECP2 coding region in 45 sporadic cases (35 with classic RTT, eight with variant forms and two males) and in seven families with two or more affected females. Following our previous report of mutations in two families and eight sporadic cases, we here present 18 additional mutations. We found 13 single nucleotide substitutions, all of which are C-->T transitions at CpG hot spots. Frameshift mutations, leading to premature termination of translation, include two single guanine (G) nucleotide deletions from a stretch of contiguous Gs, a novel four nucleotide deletion, a novel 32 nucleotide deletion in the C-terminal domain and a novel complex duplication/deletion rearrangement in the same region. When X-chromosome inactivation patterns were compared in 16 MECP2 mutation-positive and 23 mutation-negative samples, no significant differences were observed. The mutational spectrum in our subject population is similar to studies from around the world. Of over 300 MECP2 mutations reported, two-thirds are truncating mutations and one-third are missense mutations, mostly in the methyl-binding domain. Nearly 70% of all identified mutations are C-->T transitions at one of eight CpG hot spots, and about 10% are intragenic deletions or complex rearrangements that lead to frameshifts in the C-terminal region. The rate of mutation detection in the MECP2 coding region ranges from 70 to 85% in clinically diagnosed RTT and is much lower in diagnostic variants.

R133C and R168X mutations in Japanese Rett syndrome patients: a caution for misdiagnosis

Rett syndrome is a neurodevelopmental disorder characterized by regression of motor and mental abilities in females after a period of normal development. The gene, MECP2, has been reported to be responsible for Rett syndrome. Here, we report the cases who were at first misdiagnosed as having homozygous mutations, and later corrected as heterozygous ones. We analyzed the MECP2 gene in three sporadic Japanese patients with Rett syndrome. Direct sequencing by using a primer set that was originally used in the first report of MECP2 mutation suggested two types of homozygous mutations (R133C and R168X). Previous reports of these mutations with heterozygous status, as well as the general nature of dominant inheritance in Rett syndrome females and lethality in hemizygous males, urged us to confirm the homozygosity of these mutations. By using a newly designed PCR primer, we found that these mutations actually occurred heterozygously in these patients. Sequence analyses of PCR products suggested that a C/T polymorphism found upstream of these mutations caused the preferential PCR amplification of the mutated alleles. These results recommend paying attention to biased PCR amplification that may lead to misjudgment of the result for mutational analysis of the MECP2 gene.

Development of language in Rett syndrome

Ninety-nine cases of Rett syndrome (RTT) diagnosed clinically (age range 3 years 6 months to 29 years 9 months) were evaluated for the ability of language. The presence of meaningful words, vocabularies, and ages at the start and disappearance of speech were assessed. Phenotype/genotype correlation was evaluated in 22 cases in whom mutations of the genes of methyl-CpG-binding protein 2 (MECP2) existed. Fifty-five cases (55.5%) could speak some words, and of them eight cases (14.5%) spoke two-word sentences. No case had more than 40 words. The vocabularies were mainly bilabial words, known as the characteristics of the initial words in normal children. They began to utter a word between 12 and 48 months, and most of them (85.4%) before 20 months. Those who spoke two-word sentence(s) began to utter a word earlier (10.4+/-3.7 months) than others (17.1+/-9.8 months). Thirty-three cases lost their word(s) in 12-36 months. Among 22 gene-proven cases two cases with mutation of R133C and two cases with R294X had word(s), but another two cases with T158M had not. In RTT a delay in the neuronal systems involved in normal speech development was suggested and its severity seemed to depend on the loci of mutation.

A new assay for the analysis of X-chromosome inactivation in carriers with an X-linked disease

Symptoms of X-linked recessive diseases are usually observed in males, but also observed in some female carriers because of nonrandom X inactivation in which the mutated X chromosome is active and the normal X chromosomes is inactive. Therefore, it is important to investigate the patterns of X-chromosome inactivation (XCI) for clinical assessment of carriers with an X-linked disease. We have recently developed a new assay for XCI studies based on a methylation-specific polymerase chain reaction (PCR) technique. The assay involves the chemical modification of DNA with sodium bisulfite and subsequent PCR amplification. The assay is more rapid than conventional cytogenetic assays and more accurate than the current PCR-based assay for XCI studies. Because the new assay produces not only the pattern of inactive X chromosomes but also the pattern of active X chromosomes, their combination turns out to be a more reliable XCI pattern-diminishing PCR artifact. In this review, I will discuss the basics of this new assay, and its clinical applications to various X-linked diseases, including a potential application for Rett syndrome research.

The biological functions of the methyl-CpG-binding protein MeCP2 and its implication in Rett syndrome

Methylation of DNA is essential for development in the mouse and plays an important role in inactivation of the X-chromosome, genomic imprinting and gene silencing. The properties of the methyl-CpG binding proteins (MeCPs) are being proved to be the key to interpreting the connection between DNA methylation and transcriptional repression. The founder member of the family, MeCP2, consists of a single polypeptide that contains both a methyl-CpG binding domain (MBD) and transcriptional repression domain (TRD). MBD binds to a single symmetrically methylated CpG site and is responsible for chromatin localization of the protein. NMR studies have revealed that the MBD adopts a wedge-shaped molecular structure. The TRD interacts with Sin3, which is known to form complexes with histone deacetylases. MeCP2-mediated transcriptional repression may involve two distinct mechanisms, one being dependent on chromatin modification by histone deacetylation and the other being chromatin independent. Mutations in MeCP2 gene cause the X-linked neurodevelopmental disease Rett syndrome. The spectrum of mutations reflects the importance of the MBD and TRD domains. We speculate that abnormal gene expression in Rett patients leads to dysfunction of the central nervous system. We propose a genetic therapeutic approach based on activation of the wild type copy of the MeCP2 gene located in the inactive X chromosome.

Possible case of Pitt-Hopkins syndrome in sibs

In this article, we describe two sibs, a brother and sister, with severe mental retardation and multiple congenital anomalies including "coarse" facial features, short stature, seizures, hypertrichosis, short great toes, and overbreathing. Comparison of these patients with previous reports suggests that they could represent the first familial cases of the Pitt-Hopkins syndrome. The recurrence in sibs within the same family supports autosomal recessive inheritance for the condition. Variable expression of the respiratory symptoms, which has not been reported earlier, is underlined.

Deletion screening by fluorescence in situ hybridization in Rett syndrome patients

Mutations in the X-linked methyl-CpG-binding protein 2 (MECP2) gene have been found to be a cause of Rett syndrome (RTT). Mutation screening was based on various techniques including denaturing gradient gel electrophoresis, single-strand conformation polymorphism analysis, heteroduplex analysis, DNA sequencing and recently Southern Blot analysis. Mutation detection was achieved in 80% of typical RTT with a high prevalence of recurrent mutations. In order to provide further insights into the spectrum of MECP2 rearrangements in patients without any point mutation or small deletion/insertion in the coding region MECP2 gene, we screened 25 classical RTT females using fluorescence in situ hybridization analysis. No deletion were found in our group, suggesting that MECP2 gross rearrangements are a rare cause of Rett syndrome.

Gene expression profiling in postmortem Rett Syndrome brain: differential gene expression and patient classification

The identification of mutations in the transcriptional repressor methyl-CpG-binding protein 2 (MECP2) gene in Rett Syndrome (RTT) suggests that an inappropriate release of transcriptional silencing may give rise to RTT neuropathology. Despite this progress, the molecular basis of RTT neuropathogenesis remains unclear. Using multiple cDNA microarray technologies, subtractive hybridization, and conventional biochemistry, we generated comprehensive gene expression profiles of postmortem brain tissue from RTT patients and matched controls. Many glial transcripts involved in known neuropathological mechanisms were found to have increased expression in RTT brain, while decreases were observed in the expression of multiple neuron-specific mRNAs. Dramatic and consistent decreases in transcripts encoding presynaptic markers indicated a specific deficit in presynaptic development. Employing multiple clustering algorithms, it was possible to accurately segregate RTT from control brain tissue samples based solely on gene expression profile. Although previously achieved in cancers, our results constitute the first report of human disease classification using gene expression profiling in a complex tissue source such as brain.

Mutational analysis of MECP2 in Japanese patients with atypical Rett syndrome

Rett syndrome (RTT) is one of the most common neurodevelopmental disorders in females. Recently, this disease was found to be linked with mutations in the methyl-CpG-binding protein 2 gene (MECP2) and various mutations have been reported. To explore the spectrum of phenotypes resulting from MECP2 mutations, we searched for mutations in the MECP2 of 20 Japanese patients who had more than five of the criteria necessary for RTT diagnosis proposed in 1988 (The Rett Syndrome Diagnostic Criteria Work Group, Ann Neurol 23 (1988) 425) and compared the phenotype between patients with and without mutation by giving a score to each diagnostic criterion. We found four missense mutations (T158M, R133C, Y120D, and R306C), two nonsense mutations (R168X and R270X), one frameshift (726delAAAG) mutation, and one polymorphism (A201V) in ten patients (50%). This included two novel mutations (726delAAAG and Y120D). All mutations were found in the highly conserved methyl-binding and transcription repression domains. Comparison of the mean total diagnostic criterion score of the groups with and without mutation did not reveal any statistically significantly difference (P=0.28). The only difference between the groups, which was of borderline significance (P=0.051), was the sum of the scores for diagnostic criteria 2 (apparently normal psychomotor development through the first 6 months) and 5 (loss of acquired purposeful hand skills between the ages of 6 and 30 months). From these results, it is suggested that the clinical phenotype of RTT is variable and it is important to investigate the MECP2 genotype for patients having more than five criteria and not only in those who exhibit all RTT diagnostic criteria. The diagnosis of RTT is clinically difficult before 3 years of age, especially in atypical cases, but molecular analysis of the MECP2 will assist diagnosis in some patients.