Rett syndrome: clinical manifestations in males with MECP2 mutations

MECP2-related disorders while gene-based therapies are on the horizon

The emergence of new genetic tools has led to the discovery of the genetic bases of many intellectual and developmental disabilities. This creates exciting opportunities for research and treatment development, and a few genetic disorders (e.g., spinal muscular atrophy) have recently been treated with gene-based therapies. MECP2 is found on the X chromosome and regulates the transcription of thousands of genes. Loss of MECP2 gene product leads to Rett Syndrome, a disease found primarily in females, and is characterized by developmental regression, motor dysfunction, midline hand stereotypies, autonomic nervous system dysfunction, epilepsy, scoliosis, and autistic-like behavior. Duplication of MECP2 causes MECP2 Duplication Syndrome (MDS). MDS is found mostly in males and presents with developmental delay, hypotonia, autistic features, refractory epilepsy, and recurrent respiratory infections. While these two disorders share several characteristics, their differences (e.g., affected sex, age of onset, genotype/phenotype correlations) are important to distinguish in the light of gene-based therapy because they require opposite solutions. This review explores the clinical features of both disorders and highlights these important clinical differences.

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.

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.

The genetic basis of pneumococcal and staphylococcal infections: inborn errors of human TLR and IL-1R immunity

Many bacteria can cause pyogenic lesions in humans. Most of these bacteria are harmless in most individuals, but they, nevertheless, cause significant morbidity and mortality worldwide. The inherited and acquired immunodeficiencies underlying these pyogenic infections differ between bacteria. This short review focuses on two emblematic pyogenic bacteria: pneumococcus (Streptococcus pneumoniae) and Staphylococcus, both of which are Gram-positive encapsulated bacteria. We will discuss the contribution of human genetic studies to the identification of germline mutations of the TLR and IL-1R pathways.

Methyl-CpG Binding Protein 2 in Alzheimer Dementia

Despite decades of research on Alzheimer disease, understanding the complexity of the genetic and molecular interactions involved in its pathogenesis remains far from our grasp. Methyl-CpG Binding Protein 2 (MeCP2) is an important epigenetic regulator enriched in the brain, and recent findings have implicated MeCP2 as a crucial player in Alzheimer disease. Here, we provide comprehensive insights into the pathophysiological roles of MeCP2 in Alzheimer disease. In particular, we focus on how the alteration of MeCP2 expression can impact Alzheimer disease through risk genes, amyloid-β and tau pathology, cell death and neurodegeneration, and cellular senescence. We suggest that Alzheimer disease can be adversely affected by upregulated MeCP2-dependent repression of risk genes (MEF2C, ADAM10, and PM20D1), increased tau accumulation, and neurodegeneration through neuronal cell death (excitotoxicity and apoptosis). In addition, we propose that the progression of Alzheimer disease could be caused by reduced MeCP2-mediated enhancement of astrocytic and microglial senescence and consequent glial SASP (senescence-associated secretory phenotype)-dependent neuroinflammation. We surmise that any imbalance in MeCP2 function would accelerate or cause Alzheimer disease pathogenesis, implying that MeCP2 may be a potential drug target for the treatment and prevention of Alzheimer disease.

In Silico Study of Rett Syndrome Treatment-Related Genes, MECP2, CDKL5, and FOXG1, by Evolutionary Classification and Disordered Region Assessment

Rett syndrome (RTT), a neurodevelopmental disorder, is mainly caused by mutations in methyl CpG-binding protein 2 (MECP2), which has multiple functions such as binding to methylated DNA or interacting with a transcriptional co-repressor complex. It has been established that alterations in cyclin-dependent kinase-like 5 (CDKL5) or forkhead box protein G1 (FOXG1) correspond to distinct neurodevelopmental disorders, given that a series of studies have indicated that RTT is also caused by alterations in either one of these genes. We investigated the evolution and molecular features of MeCP2, CDKL5, and FOXG1 and their binding partners using phylogenetic profiling to gain a better understanding of their similarities. We also predicted the structural order-disorder propensity and assessed the evolutionary rates per site of MeCP2, CDKL5, and FOXG1 to investigate the relationships between disordered structure and other related properties with RTT. Here, we provide insight to the structural characteristics, evolution and interaction landscapes of those three proteins. We also uncovered the disordered structure properties and evolution of those proteins which may provide valuable information for the development of therapeutic strategies of RTT.

Leveraging the genetic basis of Rett syndrome to ascertain pathophysiology

Mutations in the methyl-CpG binding protein 2 (MECP2) gene cause Rett syndrome (RTT), a progressive X-linked neurological disorder characterized by loss of developmental milestones, intellectual disability and breathing abnormality. Despite being a monogenic disorder, the pathogenic mechanisms by which mutations in MeCP2 impair neuronal function and underlie the RTT symptoms have been challenging to elucidate. The seemingly simple genetic root and the availability of genetic data from RTT patients have led to the generation and characterization of a series of mouse models recapitulating RTT-associated genetic mutations. This review focuses on the studies of RTT mouse models and describe newly obtained pathogenic insights from these studies. We also highlight the potential of studying pathophysiology using genetics-based modeling approaches in rodents and suggest a future direction to tackle the pathophysiology of intellectual disability with known or complex genetic causes.

Epilepsy and genetic in Rett syndrome: A review

INTRODUCTION

Rett syndrome (RTT) is a severe X-linked neurodevelopmental disorder that primarily affects girls, with an incidence of 1:10,000-20,000. The diagnosis is based on clinical features: an initial period of apparently normal development (ages 6-12 months) followed by a rapid decline with regression of acquired motor skills, loss of spoken language and purposeful hand use, onset of hand stereotypes, abnormal gait, and growth failure. The course of the disease, in its classical form, is characterized by four stages. Three different atypical variants of the disease have been defined. Epilepsy has been reported in 60%-80% of patients with RTT; it differs among the various phenotypes and genotypes and its severity is an important contributor to the clinical severity of the disease.

METHODS

In this manuscript we reviewed literature on RTT, focusing on the different genetic entities, the correlation genotype-phenotype, and the peculiar epileptic phenotype associated to each of them.

RESULTS

Mutations in MECP2 gene, located on Xq28, account for 95% of typical RTT cases and 73.2% of atypical RTT. CDKL5 and FOXG1 are other genes identified as causative genes in atypical forms of RTT. In the last few years, a lot of new genes have been identified as causative genes for RTT phenotype.

CONCLUSIONS

Recognizing clinical and EEG patterns in different RTT variants may be useful in diagnosis and management of these patients.

MeCP2 Dysfunction in Rett Syndrome and Neuropsychiatric Disorders

Elucidating the functions of a particular gene is paramount to the understanding of how its dysfunction contributes to disease. This is especially important when the gene is implicated in multiple different disorders. One such gene is methyl-CpG-binding protein 2 (MECP2), which has been most prominently associated with the neurodevelopmental disorder Rett syndrome, as well as major neuropsychiatric disorders such as autism and schizophrenia. Being initially identified as a transcriptional regulator that modulates gene expression and subsequently also shown to be involved in other molecular events, dysfunction of the MeCP2 protein has the potential to affect many cellular processes. In this chapter, we will briefly review the functions of the MeCP2 protein and how its mutations are implicated in Rett syndrome and other neuropsychiatric disorders. We will further discuss about the mouse models that have been generated to specifically dissect the function of MeCP2 in different cell types and brain regions. It is envisioned that such thorough and targeted examination of MeCP2 functions can aid in enlightening the role that it plays in normal and dysfunctional physiological systems.

Rett Syndrome in Males: A Case Report and Review of Literature

Rett syndrome (RTT) is a neurodevelopmental disorder in which a period of normal development is followed by regression of previously acquired skills. RTT was originally thought to be present exclusively in females. However, advances in genetic testing and phenotypic identification revealed that it is not a female-only disorder as cases of males with similar phenotype were reported. RTT was considered lethal in males as it has an X-linked dominant inheritance. The purpose of this review is to report a case of RTT in young male and elaborate genetics and phenomenology of this disorder in males.

Experience-dependent MeCP2 expression in the excitatory cells of mouse visual thalamus

Loss or gain of copy number of the gene encoding the transcription factor methyl-CpG-binding protein 2 (MeCP2) leads to neurodevelopmental disorders (Rett and MeCP2 duplication syndrome), indicating that precisely regulated MeCP2 expression during development is critical for mental health. Consistent with this idea, MeCP2 null mutants exhibit synaptic regression in the dorsal lateral geniculate nucleus (dLGN), the visual relay center in the thalamus, a phenotype resembling that of animals reared in the dark during the visual sensitive period. It remains unclear how MeCP2 expression is regulated during circuit formation and maturation, especially in excitatory and inhibitory populations of neurons. We found that, concomitant with the initiation of the dark-rearing sensitive period, MeCP2 protein levels were elevated in glutamatergic but not GABAergic neurons of the dLGN. Moreover, MeCP2 expression in glutamatergic populations was selectively reduced by dark-rearing. Therefore, we propose that visual experience-dependent MeCP2 induction in glutamatergic populations is essential for synaptic maturation within the dLGN.

Rett syndrome: a neurological disorder with metabolic components

Rett syndrome (RTT) is a neurological disorder caused by mutations in the X-linked gene methyl-CpG-binding protein 2 (MECP2), a ubiquitously expressed transcriptional regulator. Despite remarkable scientific progress since its discovery, the mechanism by which MECP2 mutations cause RTT symptoms is largely unknown. Consequently, treatment options for patients are currently limited and centred on symptom relief. Thought to be an entirely neurological disorder, RTT research has focused on the role of MECP2 in the central nervous system. However, the variety of phenotypes identified in Mecp2 mutant mouse models and RTT patients implicate important roles for MeCP2 in peripheral systems. Here, we review the history of RTT, highlighting breakthroughs in the field that have led us to present day. We explore the current evidence supporting metabolic dysfunction as a component of RTT, presenting recent studies that have revealed perturbed lipid metabolism in the brain and peripheral tissues of mouse models and patients. Such findings may have an impact on the quality of life of RTT patients as both dietary and drug intervention can alter lipid metabolism. Ultimately, we conclude that a thorough knowledge of MeCP2's varied functional targets in the brain and body will be required to treat this complex syndrome.

Inherited human IRAK-1 deficiency selectively impairs TLR signaling in fibroblasts

Most members of the Toll-like receptor (TLR) and interleukin-1 receptor (IL-1R) families transduce signals via a canonical pathway involving the MyD88 adapter and the interleukin-1 receptor-associated kinase (IRAK) complex. This complex contains four molecules, including at least two (IRAK-1 and IRAK-4) active kinases. In mice and humans, deficiencies of IRAK-4 or MyD88 abolish most TLR (except for TLR3 and some TLR4) and IL-1R signaling in both leukocytes and fibroblasts. TLR and IL-1R responses are weak but not abolished in mice lacking IRAK-1, whereas the role of IRAK-1 in humans remains unclear. We describe here a boy with X-linked MECP2 deficiency-related syndrome due to a large de novo Xq28 chromosomal deletion encompassing both MECP2 and IRAK1 Like many boys with MECP2 null mutations, this child died very early, at the age of 7 mo. Unlike most IRAK-4- or MyD88-deficient patients, he did not suffer from invasive bacterial diseases during his short life. The IRAK-1 protein was completely absent from the patient's fibroblasts, which responded very poorly to all TLR2/6 (PAM₂CSK₄, LTA, FSL-1), TLR1/2 (PAM₃CSK₄), and TLR4 (LPS, MPLA) agonists tested but had almost unimpaired responses to IL-1β. By contrast, the patient's peripheral blood mononuclear cells responded normally to all TLR1/2, TLR2/6, TLR4, TLR7, and TLR8 (R848) agonists tested, and to IL-1β. The death of this child precluded long-term evaluations of the clinical consequences of inherited IRAK-1 deficiency. However, these findings suggest that human IRAK-1 is essential downstream from TLRs but not IL-1Rs in fibroblasts, whereas it plays a redundant role downstream from both TLRs and IL-1Rs in leukocytes.

Rett Syndrome Turns 50: Themes From a Chronicle: Medical Perspectives and the Human Face of Rett Syndrome

BACKGROUND

Fifty years ago Andreas Rett first described in great detail what came to be known as "Rett syndrome." Understanding girls and women with this syndrome and their families helped in many ways to revolutionize modern neurodevelopmental medicine. For some people the identification of the genetic underpinning of the syndrome and the ongoing biological research into this condition represented the peak of the scientific accomplishments in Rett syndrome. For others, it was developments in clinical research methodologies that were especially important. Above all, the patient- and family-oriented empathetic and collaborative approach to care by professionals collaborating with families has led to immense achievements, both scientific and humanistic.

AIM

The aim of this narrative was to describe the medical and personal life story of a young woman with Rett syndrome and to offer a history that highlights developments in the unraveling of this condition from its initial recognition to our current understanding.

CONCLUSION

We believe that much can be learned from the humanistic style of care provision combined with the best possible level of assisted autonomy and life enjoyment of the young woman with Rett syndrome. In addition, the approach to collaborative research by dedicated and often charitable leaders in the field can teach us many important lessons about the ethics of clinical and health services research.

MeCP2 deficiency results in robust Rett-like behavioural and motor deficits in male and female rats

Since the identification of MECP2 as the causative gene in the majority of Rett Syndrome (RTT) cases, transgenic mouse models have played a critical role in our understanding of this disease. The use of additional mammalian RTT models offers the promise of further elucidating critical early mechanisms of disease as well as providing new avenues for translational studies. We have identified significant abnormalities in growth as well as motor and behavioural function in a novel zinc-finger nuclease model of RTT utilizing both male and female rats throughout development. Male rats lacking MeCP2 (Mecp2^ZFN/y) were noticeably symptomatic as early as postnatal day 21, with most dying by postnatal day 55, while females lacking one copy of Mecp2 (Mecp2^ZFN/+) displayed a more protracted disease course. Brain weights of Mecp2^ZFN/y and Mecp2^ZFN/+rats were significantly reduced by postnatal day 14 and 21, respectively. Early motor and breathing abnormalities were apparent in Mecp2^ZFN/y rats, whereas Mecp2^ZFN/+rats displayed functional irregularities later in development. The large size of this species will provide profound advantages in the identification of early disease mechanisms and the development of appropriately timed therapeutics. The current study establishes a foundational basis for the continued utilization of this rat model in future RTT research.

A rare MeCP2_e1 mutation first described in a male patient with severe neonatal encephalopathy

Specific mutations in MECP2 cause Rett syndrome (RTT) in females whereas other mutations in the same gene cause several other syndromes in males, including X-linked intellectual disability (with and without spasticity) (OMIM 300055) and X-linked intellectual disability due to increased dosage of MECP2 (OMIM 300260). Males can also manifest an entity known as MECP2-related severe neonatal encephalopathy whose mutations are identical to those in females with RTT. We describe here the first case of MECP2-related severe neonatal encephalopathy caused by a mutation in exon one of MECP2, a mutation rarely identified in females with RTT. © 2016 Wiley Periodicals, Inc.

Epigenetics and Human Disease

Genetic causes for human disorders are being discovered at an unprecedented pace. A growing subclass of disease-causing mutations involves changes in the epigenome or in the abundance and activity of proteins that regulate chromatin structure. This article focuses on research that has uncovered human diseases that stem from such epigenetic deregulation. Disease may be caused by direct changes in epigenetic marks, such as DNA methylation, commonly found to affect imprinted gene regulation. Also described are disease-causing genetic mutations in epigenetic modifiers that either affect chromatin in trans or have a cis effect in altering chromatin configuration.

Regulatory functions and pathological relevance of the MECP2 3'UTR in the central nervous system

Methyl-CpG-binding protein 2 (MeCP2), encoded by the gene MECP2, is a transcriptional regulator and chromatin-remodeling protein, which is ubiquitously expressed and plays an essential role in the development and maintenance of the central nervous system (CNS). Highly enriched in post-migratory neurons, MeCP2 is needed for neuronal maturation, including dendritic arborization and the development of synapses. Loss-of-function mutations in MECP2 cause Rett syndrome (RTT), a debilitating neurodevelopmental disorder characterized by a phase of normal development, followed by the progressive loss of milestones and cognitive disability. While a great deal has been discovered about the structure, function, and regulation of MeCP2 in the time since its discovery as the genetic cause of RTT, including its involvement in a number of RTT-related syndromes that have come to be known as MeCP2-spectrum disorders, much about this multifunctional protein remains enigmatic. One unequivocal fact that has become apparent is the importance of maintaining MeCP2 protein levels within a narrow range, the limits of which may depend upon the cell type and developmental time point. As such, MeCP2 is amenable to complex, multifactorial regulation. Here, we summarize the role of the MECP2 3' untranslated region (UTR) in the regulation of MeCP2 protein levels and how mutations in this region contribute to autism and other non-RTT neuropsychiatric disorders.

MECP2 disorders: from the clinic to mice and back

Two severe, progressive neurological disorders characterized by intellectual disability, autism, and developmental regression, Rett syndrome and MECP2 duplication syndrome, result from loss and gain of function, respectively, of the same critical gene, methyl-CpG-binding protein 2 (MECP2). Neurons acutely require the appropriate dose of MECP2 to function properly but do not die in its absence or overexpression. Instead, neuronal dysfunction can be reversed in a Rett syndrome mouse model if MeCP2 function is restored. Thus, MECP2 disorders provide a unique window into the delicate balance of neuronal health, the power of mouse models, and the importance of chromatin regulation in mature neurons. In this Review, we will discuss the clinical profiles of MECP2 disorders, the knowledge acquired from mouse models of the syndromes, and how that knowledge is informing current and future clinical studies.

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.

Algorithmic approach for methyl-CpG binding protein 2 (MECP2) gene testing in patients with neurodevelopmental disabilities

Methyl-CpG binding protein 2 gene (MECP2) testing is indicated for patients with numerous clinical presentations, including Rett syndrome (classic and atypical), unexplained neonatal encephalopathy, Angelman syndrome, nonspecific mental retardation, autism (females), and an X-linked family history of developmental delay. Because of this complexity, a gender-specific approach for comprehensive MECP2 gene testing is described. Briefly, sequencing of exons 1 to 4 of MECP2 is recommended for patients with a Rett syndrome phenotype, unexplained neonatal encephalopathy, an Angelman syndrome phenotype (with negative 15q11-13 analysis), nonspecific mental retardation, or autism (females). Additional testing for large-scale MECP2 deletions is recommended for patients with Rett syndrome or Angelman syndrome phenotypes (with negative 15q11-13 analysis) following negative sequencing. Alternatively, testing for large-scale MECP2 duplications is recommended for males presenting with mental retardation, an X-linked family history of developmental delay, and a significant proportion of previously described clinical features (particularly a history of recurrent respiratory infections).

Distinct de novo deletions in a brother-sister pair with RTT: a case report

Rett syndrome (RTT), a neurodevelopmental disorder caused by mutations in the X-linked gene encoding methyl-CpG-binding protein2 (MeCP2), is a leading cause of mental retardation in females. Majority of cases are sporadic (99%) but some familial cases have also been observed. We describe a familial study with a brother-sister pair with symptoms of RTT and exhibiting distinct deletions in the MECP2. The non-shared de novo deletion in the two sibs provides important insights into the disease etiology, especially for male sibs showing varied phenotypes as compared to the classical ones seen in the females.

Two new Rett syndrome families and review of the literature: expanding the knowledge of MECP2 frameshift mutations

BACKGROUND

Rett syndrome (RTT) is an X-linked dominant neurodevelopmental disorder, which is usually caused by de novo mutations in the MECP2 gene. More than 70% of the disease causing MECP2 mutations are eight recurrent C to T transitions, which almost exclusively arise on the paternally derived X chromosome. About 10% of the RTT cases have a C-terminal frameshift deletion in MECP2. Only few RTT families with a segregating MECP2 mutation, which affects female carriers with a phenotype of mental retardation or RTT, have been reported in the literature. In this study we describe two new RTT families with three and four individuals, respectively, and review the literature comparing the type of mutations and phenotypes observed in RTT families with those observed in sporadic cases. Based on these observations we also investigated origin of mutation segregation to further improve genetic counselling.

METHODS

MECP2 mutations were identified by direct sequencing. XCI studies were performed using the X-linked androgen receptor (AR) locus. The parental origin of de novo MECP2 frameshift mutations was investigated using intronic SNPs.

RESULTS

In both families a C-terminal frameshift mutation segregates. Clinical features of the mutation carriers vary from classical RTT to mild mental retardation. XCI profiles of the female carriers correlate to their respective geno-/phenotypes. The majority of the de novo frameshift mutations occur on the paternally derived X chromosome (7/9 cases), without a paternal age effect.

CONCLUSIONS

The present study suggests a correlation between the intrafamilial phenotypic differences observed in RTT families and their respective XCI pattern in blood, in contrast to sporadic RTT cases where a similar correlation has not been demonstrated. Furthermore, we found de novo MECP2 frameshift mutations frequently to be of paternal origin, although not with the same high paternal occurrence as in sporadic cases with C to T transitions. This suggests further investigations of more families. This study emphasizes the need for thorough genetic counselling of families with a newly diagnosed RTT patient.

Phenotypic and genotypic variability in four males with MECP2 gene sequence aberrations including a novel deletion

The MECP2 gene mutations cause Rett syndrome (RTT) (OMIM: 312750), an X-linked dominant disorder primarily affecting girls. Until RTT was considered lethal in males, although now approximately 60 cases have been reported. Males with MECP2 mutations present with a broad spectrum of phenotypes ranging from neonatal encephalopathy to nonsyndromic mental retardation (MR). Four boys (aged, 3-11 y) were evaluated for MR. Patient 1 had autistic features. Patients 2 and 3 were brothers both presenting with psychomotor delay. Patient 4 showed dysmorphic features and behavioral problems reminiscent of FXS. All patients had a normal 46, XY karyotype and three were tested for FXS with negative results. MECP2 gene analysis of exons 3 and 4 was performed using methods based on the PCR, including Enzymatic Cleavage Mismatched Analysis (ECMA) and direct sequencing. Patient 1 presented somatic mosaicism for the classic RTT p.R106W mutation and patient 4 carried the p.T203M polymorphism. Analysis of the mothers in both cases revealed normal DNA sequences. Patients 2 and 3 had a novel deletion (c.1140del86) inherited from their unaffected mother. MECP2 gene mutations may be considered a rare cause of MR in males although great phenotypic variation hinders genotype-phenotype correlation.

DNA methylation and methyl-CpG binding proteins: developmental requirements and function

DNA methylation is a major epigenetic modification in the genomes of higher eukaryotes. In vertebrates, DNA methylation occurs predominantly on the CpG dinucleotide, and approximately 60% to 90% of these dinucleotides are modified. Distinct DNA methylation patterns, which can vary between different tissues and developmental stages, exist on specific loci. Sites of DNA methylation are occupied by various proteins, including methyl-CpG binding domain (MBD) proteins which recruit the enzymatic machinery to establish silent chromatin. Mutations in the MBD family member MeCP2 are the cause of Rett syndrome, a severe neurodevelopmental disorder, whereas other MBDs are known to bind sites of hypermethylation in human cancer cell lines. Here, we review the advances in our understanding of the function of DNA methylation, DNA methyltransferases, and methyl-CpG binding proteins in vertebrate embryonic development. MBDs function in transcriptional repression and long-range interactions in chromatin and also appear to play a role in genomic stability, neural signaling, and transcriptional activation. DNA methylation makes an essential and versatile epigenetic contribution to genome integrity and function.

CNV and nervous system diseases--what's new?

Several new genomic disorders caused by copy number variation (CNV) of genes whose dosage is critical for the physiological function of the nervous system have been recently identified. Dup(7)(q11.23) patients carry duplications of the genomic region deleted in Williams-Beuren syndrome, they are characterized by prominent speech delay. The phenotypes of Potocki-Lupski syndrome and MECP2 duplication syndrome were neuropsychologically examined in detail, which revealed autism as an endophenotype and a prominent behavioral feature of these disorders. Tandem duplication of LMNB1 was reported to cause adult-onset autosomal dominant leukodystrophy. PAFAH1B1/LIS1 and YWHAE, which were deleted in isolated lissencephaly (PAFAH1B1/LIS1 alone) and Miller-Dieker syndrome (both genes), were found to be duplicated in patients with developmental delay. Finally, two novel microdeletion syndromes affecting 17q21.31 and 15q13.3, as well as their reciprocal duplications, were also identified. In this review, we provide an overview of the phenotypic manifestation of these syndromes and the rearrangements causing them.

Mutations in the MECP2 gene are not a major cause of Rett syndrome-like or related neurodevelopmental phenotype in male patients

Rett syndrome is a genetic neurodevelopmental disorder that affects mainly girls, but mutations in the causative MECP2 gene have also been identified in boys with classic Rett syndrome and Rett syndrome-like phenotypes. We have studied a group of 28 boys with a neurodevelopmental disorder, 13 of which with a Rett syndrome-like phenotype; the patients had diverse clinical presentations that included perturbations of the autistic spectrum, microcephaly, mental retardation, manual stereotypies, and epilepsy. We analyzed the complete coding region of the MECP2 gene, including the detection of large rearrangements, and we did not detect any pathogenic mutations in the MECP2 gene in these patients, in whom the genetic basis of disease remained unidentified. Thus, additional genes should be screened in this group of patients.

Severe congenital encephalopathy caused by MECP2 null mutations in males: central hypoxia and reduced neuronal dendritic structure

Non-mosaic males with a 46,XY karyotype and a MECP2 null mutation display a phenotype of severe neonatal-onset encephalopathy that is distinctly different from Rett syndrome (RTT). To increase awareness of this rare disorder, we are reporting novel findings in a sporadic case, compare them to 16 previously reported cases and establish salient criteria for clinical diagnosis. The proband suffered from general hypotonia and hypoxia caused by hypoventilation and irregular breathing. He developed abnormal movements, seizures and electroencephalogram abnormalities. He failed to thrive and to reach any motor milestones and died at 15 months from central respiratory failure without a diagnosis. In a muscle biopsy, type II fibers were reduced in diameter, indicating central hypoxia. At autopsy, the brain was small with disproportionate reduction of the frontal and temporal lobes. Synaptophysin staining of synaptic vesicles was greatly reduced in cerebellar and spinal cord sections. Analysis of Golgi-stained pyramidal neurons from cortical layers III and V of the frontal and temporal lobes revealed drastically diminished dendritic trees. Post-mortem MECP2 mutation analysis on DNA and RNA from fibroblasts revealed a novel de novo 9-nucleotide deletion including the intron 3/exon 4 splice junction. The two nucleotides flanking the deletion form a new splice site, and the aberrantly spliced transcript lacks seven nucleotides (r.378_384delTCCCCAG), causing a frameshift and premature termination codon (p.I126fsX11). Males with congenital encephalopathy, not females with RTT, represent the true human counterpart for the commonly studied Mecp2-/y mouse model and provide unique insight into the mechanisms of MeCP2 deficiency.

The overlapping spectrum of rett and angelman syndromes: a clinical review

Rett and Angelman syndromes comprise part of the spectrum of neurologic disorders associated with autism. Their clinical presentations overlap, with both presenting in later infancy with global developmental delays, severe speech and communication impairments, progressive microcephaly, seizures, autistic behaviors, and characteristic albeit different movement disorders and stereotypic hand movements. Although other features can help differentiate these disorders, significant phenotypic overlap and variation in severity sometimes cloud the underlying diagnosis. Rett syndrome is caused by a mutation in the MECP2 gene located on Xq28, whereas Angelman syndrome results from the loss of UBE3A function on chromosomal region 15q11-q13 related to a variety of molecular genetic mechanisms. Recent advances have uncovered interactions between these and other genes that affect the function and structure of neurons in the brain. The reversal of symptoms of Rett syndrome in a mature mouse model suggests the possibility for treatment of these and perhaps other autism-related disorders in the future.

Mechanisms of disease: neurogenetics of MeCP2 deficiency

Rett syndrome (RTT) is unique among genetic, chromosomal and other developmental disorders because of its extreme female gender bias, early normal development, and subsequent developmental regression with loss of motor and language skills. RTT is caused by heterozygosity for mutations in the X-linked gene MECP2, which encodes methyl-CpG binding protein 2. MeCP2 is a multifunctional protein that can act as an architectural chromatin-binding protein, a function that is unrelated to its ability to bind methyl-CpG and to attract chromatin modification complexes. Inactivating mutations that cause RTT in females are not prenatally lethal in males, but lead to profound congenital encephalopathy. Molecular diagnoses of RTT, through demonstration of a MECP2 mutation, made at an early stage of the disorder, usually confirm the sporadic nature and very low recurrence risk of the condition. A positive DNA test result, however, also predicts the inevitable clinical course, given the lack of effective intervention. Initial hypotheses indicating that the MeCP2 protein acts as a genome-wide transcriptional repressor were not confirmed by global gene expression studies in various tissues of individuals with RTT and mouse models of MeCP2 deficiency. Rather, recent evidence points to low-magnitude effects of a small number of genes--including the brain--derived neurotrophic factor pathway and glucocorticoid response genes-that might affect formation and maturation of synapses or synaptic function in postmitotic neurons.

MECP2 mutations in males

Rett syndrome (RS; MIM 312750) is a severe neurological disorder affecting exclusively females. Its prevalence is about 1 in 10,000 female births, and it is a prominent cause of profound mental handicap in women. RS is caused by mutations in the X-linked methyl CpG-binding protein 2 (MECP2) gene. These mutations were initially thought to be lethal in males. However, MECP2 mutations are now frequently identified in mentally retarded male patients. The frequency of disease-causing MECP2 mutations in this population is between 1.3% and 1.7%. Surprisingly, MECP2 mutations in males are responsible for a wide spectrum of neurological disorders, ranging from mild mental retardation to severe neonatal encephalopathy. The aim of this review is to describe the nature of the MECP2 mutations identified in male patients to date and their associated phenotypes.

Increased MECP2 gene copy number as the result of genomic duplication in neurodevelopmentally delayed males

PURPOSE

Mutations in the MECP2 gene are associated with Rett syndrome, an X-linked mental retardation disorder in females. Mutations also cause variable neurodevelopmental phenotypes in rare affected males. Recent clinical testing for MECP2 gene rearrangements revealed that entire MECP2 gene duplication occurs in some males manifesting a progressive neurodevelopmental syndrome.

METHODS

Clinical testing through quantitative DNA methods and chromosomal microarray analysis in our laboratories identified seven male patients with increased MECP2 gene copy number.

RESULTS

Duplication of the entire MECP2 gene was found in six patients, and MECP2 triplication was found in one patient with the most severe phenotype. The Xq28 duplications observed in these males are unique and vary in size from approximately 200 kb to 2.2 Mb. Three of the mothers who were tested were asymptomatic duplication carriers with skewed X-inactivation. In silico analysis of the Xq28 flanking region showed numerous low-copy repeats with potential roles in recombination.

CONCLUSIONS

These collective data suggest that increased MECP2 gene copy number is mainly responsible for the neurodevelopmental phenotypes in these males. These findings underscore the allelic and phenotypic heterogeneity associated with the MECP2 gene and highlight the value of molecular analysis for patient diagnosis, family members at risk, and genetic counseling.

Mutation analysis of the MECP2 gene in patients of Slavic origin with Rett syndrome: novel mutations and polymorphisms

Rett syndrome (RTT), an X-linked dominant neurodevelopmental disorder in females, is caused mainly by de novo mutations in the methyl-CpG-binding protein 2 gene (MECP2). Here we report mutation analysis of the MECP2 gene in 87 patients with RTT from the Czech and Slovak Republics, and Ukraine. The patients, all girls, with classical RTT were investigated for mutations using bi-directional DNA sequencing and conformation sensitive gel electrophoresis analysis of the coding sequence and exon/intron boundaries of the MECP2 gene. Restriction fragment length polymorphism analysis was performed to confirm the mutations that cause the creation or abolition of the restriction site. Mutation-negative cases were subsequently examined by multiple ligation-dependent probe amplification (MLPA) to identify large deletions. Mutation screening revealed 31 different mutations in 68 patients and 12 non-pathogenic polymorphisms. Six mutations have not been previously published: two point mutations (323T>A, 904C>T), three deletions (189_190delGA, 816_832del17, 1069delAGC) and one deletion/inversion (1063_1236del174;1189_1231inv43). MLPA analysis revealed large deletions in two patients. The detection rate was 78.16%. Our results confirm the high frequency of MECP2 mutations in females with RTT and provide data concerning the mutation heterogeneity in the Slavic population.

Rett syndrome: new clinical and molecular insights

In this review, we give a clinical overview of Rett syndrome (RTT), and provide a framework for clinical and molecular approaches to the diagnosis of this severe neurodevelopmental disorder. We also discuss issues that need to be considered in the management of RTT patients, and raise some of the challenges associated with genetic counselling.

Genotype and early development in Rett syndrome: the value of international data

BACKGROUND

Rett syndrome is a neurodevelopmental disorder mostly affecting females and caused by mutations in the MECP2 gene. Originally the syndrome was characterised as having a normal prenatal and perinatal period with later regression. Previous work has speculated that the girl with Rett syndrome may not be normal at birth.

AIMS

to examine whether early development between birth and ten months varies by genotype in Rett syndrome.

METHODS

cases were sourced from two databases, the Australian Rett Syndrome Database (est. 1993) and the newly formed InterRett - IRSA Rett Phenotype Database. Data available on 320 cases included information provided by parents on perinatal problems, early developmental behaviour and mobility. Problem scores, mobility scores and a total composite score for each mutation were generated and compared.

RESULTS

overall, 58% of respondents noted unusual behaviour during the first six months and 70.6% from the period between 6 and 10 months of life. Statistically significant differences were detected between some of the common mutations. Infants with R294X (P=0.05) and R133C (P=0.03) were less likely than those with R255X to have problems in the perinatal period. The most severe profile overall for early development was associated with mutations R255X and R270X.

CONCLUSION

This is the largest study to date examining the effects of individual mutations in Rett syndrome. With the ongoing case ascertainment and expansion of InterRett, sample size will increase rapidly and provide improved statistical power for future analyses. Results from this study will contribute to understanding the mechanism of early development in Rett syndrome and determining if and at which time(s) early intervention might be feasible.

Clinical profile of a male with Rett syndrome

We describe a clinical profile of a male with Rett syndrome who presented initially with significant axial and peripheral hypotonia, head and truncal titubation and global delay. He is non-ambulatory, lost the few words he had learned and gradually developed hand stereotypes, breathing difficulties, seizures, scoliosis and has osteoporosis sleep problems and sludging in his gall bladder. Prior to diagnosis he underwent comprehensive neurological, metabolic and genetic investigations. After his older sister was diagnosed with atypical Rett syndrome; MECP2 mutation studies on him revealed a pathogenic mutation. His mother is a Rett carrier with a skewed inactivation of chromosome X. Clinical signs and symptoms required to meet the criteria for diagnosis of Rett syndrome have gradually evolved over time. This case demonstrates an unusual family history for Rett syndrome and alerts readers to the utility of screening males for Rett syndrome.

MECP2 mutations or polymorphisms in mentally retarded boys: diagnostic implications

BACKGROUND

Among the well characterized X-linked conditions causing mental retardation, mutations in the methyl-CpG-binding protein 2 gene (MECP2) in Xq28 have been found in up to 85% of patients with Rett syndrome, a neurologic disorder which, in addition to other symptoms, severely affects higher cognitive functions in females. Mutations in the MECP2 gene are involved in a broad spectrum of phenotypes from classical Rett syndrome to mild intellectual difficulties in females and neonatal encephalopathy in males. Recently, mutations in the MECP2 gene were reported in males with non-specific mental retardation suggesting that defects in MECP2 could be responsible for up to 2% of X-linked mental retardation.

METHODS

We screened by denaturing high-pressure liquid chromatography the entire coding region and flanking intronic sequences of the MECP2 gene in a cohort of 354 mentally retarded males found negative for an expansion across the FRAXA CGG repeat and in a family in which a boy and his sister were mentally retarded.

RESULTS

We identified mainly silent polymorphisms within the MECP2 gene, together with four sequence alterations of unknown significance, i.e. three missense mutations (T197M, T228S, and P376S) and one substitution at position -19 in intron 3 (378-19delT). Further familial investigations allowed us to ruled out a pathogenic effect for the intronic variant, the T228S and the P376S missense mutations.

CONCLUSIONS

These results confirm that MECP2 mutations in males are far more rare than initially thought and call for a careful evaluation of the pathogenicity of the MECP2 missense mutations identified in mentally retarded males before genetic counseling is proposed to the relatives.

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.

Molecular diagnosis of Rett syndrome

In 1999, mutations in the MECP2 gene were identified as the primary cause of Rett syndrome. MECP2 mutations can be found in 70% to 80% of all clinically defined Rett syndrome cases; in classic Rett syndrome, this frequency is even higher. In most cases, missense and nonsense mutations affecting functionally important domains can be found. Additionally, a hot spot for small deletions has been defined, and several gross rearrangements have also been described. Among female individuals with Rett syndrome, the spectrum of clinical phenotypes is broad, but most fulfill the diagnostic criteria. In contrast, male individuals with mutations in the MECP2 gene are rare, and only a minority have clinical symptoms resembling Rett syndrome.

Duplication of the MECP2 region is a frequent cause of severe mental retardation and progressive neurological symptoms in males

Loss-of-function mutations of the MECP2 gene at Xq28 are associated with Rett syndrome in females and with syndromic and nonsyndromic forms of mental retardation (MR) in males. By array comparative genomic hybridization (array-CGH), we identified a small duplication at Xq28 in a large family with a severe form of MR associated with progressive spasticity. Screening by real-time quantitation of 17 additional patients with MR who have similar phenotypes revealed three more duplications. The duplications in the four patients vary in size from 0.4 to 0.8 Mb and harbor several genes, which, for each duplication, include the MR-related L1CAM and MECP2 genes. The proximal breakpoints are located within a 250-kb region centromeric of L1CAM, whereas the distal breakpoints are located in a 300-kb interval telomeric of MECP2. The precise size and location of each duplication is different in the four patients. The duplications segregate with the disease in the families, and asymptomatic carrier females show complete skewing of X inactivation. Comparison of the clinical features in these patients and in a previously reported patient enables refinement of the genotype-phenotype correlation and strongly suggests that increased dosage of MECP2 results in the MR phenotype. Our findings demonstrate that, in humans, not only impaired or abolished gene function but also increased MeCP2 dosage causes a distinct phenotype. Moreover, duplication of the MECP2 region occurs frequently in male patients with a severe form of MR, which justifies quantitative screening of MECP2 in this group of patients.

X-linked mental retardation: further lumping, splitting and emerging phenotypes

X-linked mental retardation (XLMR) is a very heterogeneous condition, subdivided in two categories mainly based on clinical features: syndromic XLMR (MRXS) and non-syndromic XLMR (MRX). Although it was thought that 20-25% of mental retardation (MR) in males was caused by monogenetic X-linked factors, recent estimations are lower: in the range of 10-12%. The number of identified genes involved in XLMR has been rapidly growing in the past years. Subsequently, an increasing number of patients and families have been reported in which mutations in XLMR genes have been identified. It was observed previously, that mutations in several of XLMR genes can result in syndromic and in non-syndromic phenotypes. This observation has been confirmed for the more recently identified genes. Therefore, in this review, focus has been given on the clinical data and on phenotype-genotype correlations for those genes implicated in both non-syndromic and syndromic XLMR.

Mutations in the X-linked cyclin-dependent kinase-like 5 (CDKL5/STK9) gene are associated with severe neurodevelopmental retardation

Recently, we showed that truncation of the X-linked cyclin-dependent kinase-like 5 (CDKL5/STK9) gene caused mental retardation and severe neurological symptoms in two female patients. Here, we report that de novo missense mutations in CDKL5 are associated with a severe phenotype of early-onset infantile spasms and clinical features that overlap those of other neurodevelopmental disorders, such as Rett syndrome and Angelman syndrome. The mutations are located within the protein kinase domain and affect highly conserved amino acids; this strongly suggests that impaired CDKL5 catalytic activity plays an important role in the pathogenesis of this neurodevelopmental disorder. In view of the overlapping phenotypic spectrum of CDKL5 and MECP2 mutations, it is tempting to speculate that these two genes play a role in a common pathogenic process.

Mutations of CDKL5 cause a severe neurodevelopmental disorder with infantile spasms and mental retardation

Rett syndrome (RTT) is a severe neurodevelopmental disorder caused, in most classic cases, by mutations in the X-linked methyl-CpG-binding protein 2 gene (MECP2). A large degree of phenotypic variation has been observed in patients with RTT, both those with and without MECP2 mutations. We describe a family consisting of a proband with a phenotype that showed considerable overlap with that of RTT, her identical twin sister with autistic disorder and mild-to-moderate intellectual disability, and a brother with profound intellectual disability and seizures. No pathogenic MECP2 mutations were found in this family, and the Xq28 region that contains the MECP2 gene was not shared by the affected siblings. Three other candidate regions were identified by microsatellite mapping, including 10.3 Mb at Xp22.31-pter between Xpter and DXS1135, 19.7 Mb at Xp22.12-p22.11 between DXS1135 and DXS1214, and 16.4 Mb at Xq21.33 between DXS1196 and DXS1191. The ARX and CDKL5 genes, both of which are located within the Xp22 region, were sequenced in the affected family members, and a deletion of nucleotide 183 of the coding sequence (c.183delT) was identified in CDKL5 in the affected family members. In a screen of 44 RTT cases, a single splice-site mutation, IVS13-1G-->A, was identified in a girl with a severe phenotype overlapping RTT. In the mouse brain, Cdkl5 expression overlaps--but is not identical to--that of Mecp2, and its expression is unaffected by the loss of Mecp2. These findings confirm CDKL5 as another locus associated with epilepsy and X-linked mental retardation. These results also suggest that mutations in CDKL5 can lead to a clinical phenotype that overlaps RTT. However, it remains to be determined whether CDKL5 mutations are more prevalent in specific clinical subgroups of RTT or in other clinical presentations.

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.

Rett syndrome: a prototypical neurodevelopmental disorder

Rett syndrome, one of the leading causes of mental retardation and developmental regression in girls, is the first pervasive developmental disorder with a known genetic cause. The majority of cases of sporadic Rett syndrome are caused by mutations in the gene encoding methyl-CpG-binding protein 2 (MeCP2). MeCP2 binds methylated DNA and likely regulates gene expression and chromatin structure. Genotype/phenotype analysis revealed that the phenotypic spectrum of MECP2 mutations in humans is broader than initially suspected: Mutations have been discovered in Rett syndrome variants, mentally retarded males, and autistic children. A variety of in vivo and in vitro models has been developed that allow analysis of MeCP2 function and pathogenic studies of Rett syndrome. Because the neuropathology of Rett syndrome shares certain features with other neurodevelopmental disorders, a common pathogenic process may underlie these disorders. Thus, Rett syndrome is a prototype for the genetic, molecular, and neurobiological analysis of neurodevelopmental disorders.

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.

MECP2 gene mutations in non-syndromic X-linked mental retardation: Phenotype-genotype correlation

Non-syndromic X-linked mental retardation (MRX) is a frequent cause of inherited mental retardation. It is a heterogeneous condition in which the first 12 genes discovered to date explain no more than 15% of the MRX situations ascertained by recurrence in multiplex families. In Rett syndrome (RTT), an X-linked dominant condition mostly sporadic and usually lethal in males, most affected females have been shown to be mutated in the Methyl-CpG binding protein 2 gene (MECP2) that maps at Xq28. Some mentally retarded males related to RTT females carry the same mutation. Several MRX families mapping to Xq28 were subsequently tested for MECP2 and a causative mutation was discovered in three families, suggesting that it could be one of the main genes involved in MRX. We report here the corresponding phenotypes in these three families of increasing severity. In family 1, an in-frame deletion DeltaP387-M466 was found in the 3' region. The patients had severe to mild non-progressive MR, with better motor skills than verbal abilities. In family 2, an Arg to Trp substitution (R167W) was found between the transcription repression domain (TRD) and the methyl binding domain (MBD). The patients had brisk reflexes and essential tremor with mild and non-progressive MR, poor motor co-ordination and written language difficulties. In the third family (MRX16), a Glu to Gly substitution (E137G) was found in the MBD. The patients had manifestations similar to those of family 2, but MR was mild to moderate, speech articulation was poor and some had verbal stereotypies. Regression of language skills was suspected in three patients. Phenotype-genotype correlation could thus be suspected and is discussed in these three families.

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.