Tsix-Mecp2 female mouse model for Rett syndrome reveals that low-level MECP2 expression extends life and improves neuromotor function.

Rett syndrome (RTT) is a severe neurodevelopmental disorder caused by a mutation in the X-linked methyl-CpG-binding protein 2 (MECP2). There is currently no disease-specific treatment, but MECP2 restoration through reactivation of the inactive X (Xi) has been of considerable interest. Progress toward an Xi-reactivation therapy has been hampered by a lack of suitable female mouse models. Because of cellular mosaicism due to random X-chromosome inactivation (XCI), Mecp2+/- heterozygous females develop only mild RTT. Here, we create an improved female mouse model by introducing a mutation in Tsix, the antisense regulator of XCI allelic choice. Tsix-Mecp2 mice show reduced MECP2 mosaicism and closely phenocopy the severely affected Mecp2-null males. Tsix-Mecp2 females demonstrate shortened lifespan, motor weakness, tremors, and gait disturbance. Intriguingly, they also exhibit repetitive behaviors, as is often seen in human RTT, including excessive grooming and biting that result in self-injury. With a Tsix allelic series, we vary MECP2 levels in brain and demonstrate a direct, but nonlinear correlation between MECP2 levels and phenotypic improvement. As little as 5-10% MECP2 restoration improves neuromotor function and extends lifespan five- to eightfold. Our study thus guides future pharmacological strategies and suggests that partial MECP2 restoration could have disproportionate therapeutic benefit.

Breathing disturbances in a model of Rett syndrome: A potential involvement of the glycine receptor α3 subunit?

The glycine receptor α3 subunit is known to be a target for cAMP/PKA-mediated phosphorylation and regulation. Mice that lack this subunit are apparently normal but the 5-HT1A-receptor mediated modulation of respiratory network activity is disturbed. Since the intracellular cAMP-concentration is reduced in mice that lack the transcriptional modulator methyl-CpG-binding protein 2 (MeCP2) gene, we aimed to test if the α3 subunit of the glycine receptor is involved in the development of the breathing phenotype of MeCP2-deficient mice (Mecp2-/y). Therefore, we generated a double knock-out mouse line that lacks both the Mecp2 gene as well as the gene (Glra3) for the α3 subunit of the ionotropic glycine receptor. As compared to WT and Glra3-/- mice, both Mecp2-/y mice and Mecp2-/y; Glra3-/- mice (DKO) showed a slower respiratory rate and a tendency towards higher numbers of apneas. Interestingly, the irregularity of the breathing was significantly reduced in DKO as compared to Mecp2-/y littermates. In the light of the unaltered survival of DKO mice, however, the contribution of the glycine receptor α3 subunit for development and progression of the breathing disturbances in the mouse model of Rett syndrome appears to be only of minor relevance.

CX3CR1 ablation ameliorates motor and respiratory dysfunctions and improves survival of a Rett syndrome mouse model.

Rett syndrome (RTT) is a neurodevelopmental disorder caused by loss-of-function mutations in the gene encoding MeCP2, an epigenetic modulator that binds the methyl CpG dinucleotide in target genes to regulate transcription. Previously we and others reported a role of microglia in the pathophysiology of RTT. Because microglia in the Mecp2 knockout (Mecp2KO) mouse model of RTT over-produce neurotoxic mediators glutamate and reactive oxygen species, we hypothesize that blocking neuron-microglia interaction by ablation of CX3CR1, a chemokine receptor expressed in microglia/myeloid cells mediating such interaction by pairing with its neuronal ligand CX3CL1, would ameliorate the RTT-like phenotype in Mecp2KO mice. Here we report that CX3CR1 ablation prolonged the lifespan of Mecp2KO mice from a median survival of 54.5-74days, and significantly improved the body weight gain, symptomatic scores, major respiratory parameters, and motor coordination and performance. CX3CR1 ablation rectified previously identified histological abnormalities in the Mecp2KO brain such as neuronal soma size in hippocampal CA2, and the number, soma size, and process complexity of microglia. Moreover, CX3CR1 ablation enhanced the neurotrophic action of microglia in Mecp2KO mice by producing higher amount of insulin-like growth factor 1. Our data support a role of myeloid cells/microglia in RTT and suggest a novel therapeutic approach for RTT by targeting CX3CR1 with specific antagonists or genetic downregulation.

Loss of MeCP2 Causes Urological Dysfunction and Contributes to Death by Kidney Failure in Mouse Models of Rett Syndrome.

Rett Syndrome (RTT) is a neurodevelopmental disorder characterized by loss of acquired skills during development, autonomic dysfunction, and an increased risk for premature lethality. Clinical experience identified a subset of individuals with RTT that present with urological dysfunction including individuals with frequent urinary tract infections, kidney stones, and urine retention requiring frequent catheterization for bladder voiding. To determine if urologic dysfunction is a feature of RTT, we queried the Rett Syndrome Natural History Study, a repository of clinical data from over 1000 individuals with RTT and found multiple instances of urological dysfunction. We then evaluated urological function in a mouse model of RTT and found an abnormal pattern of micturition. Both male and female mice possessing Mecp2 mutations show a decrease in urine output per micturition event. Furthermore, we identified signs of kidney failure secondary to urethral obstruction. Although genetic strain background significantly affects both survival and penetrance of the urethral obstruction phenotype, survival and penetrance of urethral obstruction do not directly correlate. We have identified an additional phenotype caused by loss of MeCP2, urological dysfunction. Furthermore, we urge caution in the interpretation of survival data as an endpoint in preclinical studies, especially where causes of mortality are poorly characterized.

Surgical fusion of early onset severe scoliosis increases survival in Rett syndrome: a cohort study.

AIM: Scoliosis is a common comorbidity in Rett syndrome and spinal fusion may be recommended if severe. We investigated the impact of spinal fusion on survival and risk of severe lower respiratory tract infection in Rett syndrome. METHOD: Data were ascertained from hospital medical records, the Australian Rett Syndrome Database, a longitudinal and population-based registry, and from the Australian Institute of Health and Welfare National Death Index database. Cox regression and generalized estimating equation models were used to estimate the effects of spinal surgery on survival and severe respiratory infection respectively in 140 females who developed severe scoliosis (Cobb angle ≥45°) before adulthood. RESULTS: After adjusting for mutation type and age of scoliosis onset, the rate of death was lower in the surgery group (hazard ratio [HR] 0.30, 95% confidence interval [CI] 0.12-0.74; p=0.009) compared to those without surgery. Rate of death was particularly reduced for those with early onset scoliosis (HR 0.17, 95% CI 0.06-0.52; p=0.002). There was some evidence to suggest that spinal fusion was associated with a reduction in risk of severe respiratory infection among those with early onset scoliosis (risk ratio 0.41, 95% CI 0.16-1.03; p=0.06). INTERPRETATION: With appropriate cautions, spinal fusion confers an advantage to life expectancy in Rett syndrome.

The molecular basis of variable phenotypic severity among common missense mutations causing Rett syndrome.

Rett syndrome is caused by mutations in the X-linked MECP2 gene, which encodes a chromosomal protein that binds to methylated DNA. Mouse models mirror the human disorder and therefore allow investigation of phenotypes at a molecular level. We describe an Mecp2 allelic series representing the three most common missense Rett syndrome (RTT) mutations, including first reports of Mecp2[R133C] and Mecp2[T158M] knock-in mice, in addition to Mecp2[R306C] mutant mice. Together these three alleles comprise ∼25% of all RTT mutations in humans, but they vary significantly in average severity. This spectrum is mimicked in the mouse models; R133C being least severe, T158M most severe and R306C of intermediate severity. Both R133C and T158M mutations cause compound phenotypes at the molecular level, combining compromised DNA binding with reduced stability, the destabilizing effect of T158M being more severe. Our findings contradict the hypothesis that the R133C mutation exclusively abolishes binding to hydroxymethylated DNA, as interactions with DNA containing methyl-CG, methyl-CA and hydroxymethyl-CA are all reduced in vivo. We find that MeCP2[T158M] is significantly less stable than MeCP2[R133C], which may account for the divergent clinical impact of the mutations. Overall, this allelic series recapitulates human RTT severity, reveals compound molecular aetiologies and provides a valuable resource in the search for personalized therapeutic interventions.

The Changing Face of Survival in Rett Syndrome and MECP2-Related Disorders.

PURPOSE: Survival in Rett syndrome remains unclear. Although early estimates were grim, more recent data suggest that survival into adulthood is typical. We aimed to define survival in Rett syndrome more clearly and identify risk factors for early death. METHODS: Participants with clinical Rett Syndrome or methyl-CpG-binding protein 2 mutations without clinical RTT were recruited through the Rett Syndrome Natural History study from 2006 to 2015. Clinical details were collected, and survival was determined using the Kaplan-Meier estimator. Risk factors were assessed using Cox proportional hazards models. RESULTS: Among 1189 valid participants, 51 died (range 3.9-66.6 years) during the 9-year follow-up period. Those who died included 36 (3.9%) classic Rett syndrome females, 5 (5.9%) atypical severe Rett syndrome females, 1 (2.4%) non-Rett syndrome female, the single atypical severe male, 6 (30%) non-Rett syndrome males, and 2 (7.1%) methyl-CpG-binding protein 2 duplication syndrome males. All atypical mild Rett syndrome females, methyl-CpG-binding protein 2 duplication syndrome females, and the single classic Rett syndrome male remain alive. Most deaths were due to cardiorespiratory issues. Only one died from severe malnutrition, scoliosis, and extreme frailty. Survival for classic and atypical Rett syndrome was greater than 70% at 45 years. Overall severity and several modifiable risk factors, including ambulation, weight, and seizures, were associated with mortality in classic Rett syndrome. CONCLUSIONS: Survival into the fifth decade is typical in Rett syndrome, and death due to extreme frailty has become rare. Although the leading cause of death remains cardiorespiratory compromise, many risk factors for early death are modifiable. Intense therapeutic interventions could further improve the prognosis for individuals with Rett syndrome.

Epidemiology of Rett syndrome in Serbia: prevalence, incidence and survival.

BACKGROUND: Rett syndrome (RTT) is a severe neurodevelopmental disorder that represents the second most common cause of mental retardation in females. However, incidence and prevalence of RTT are scarcely reported. METHODS: A retrospective study included all patients with RTT diagnosed between 1981 and 2012 in Serbia. Estimation of incidence and prevalence was calculated on the basis of vital statistics reported by Statistical Office of Republic of Serbia. RESULTS: From 1981 to 2012, RTT has been diagnosed in 102 girls in Serbia. Incidence of RTT in Serbia is estimated at 0.586:10,000 female live births. We estimated the prevalence of RTT in population of females younger than 19 years at 1:8,439. Death occurred in 19 patients (18.63%), with pneumonia as the most common cause. The lethal outcome by the age of 12 years could be expected for 11% of patients. The mean age at diagnosis was 3.5 years and we have confirmed a significant trend towards earlier dianosis during studied period. CONCLUSIONS: Rett syndrome incidence in Serbia is in accordance with reports from other countries. Serbian RTT patients have increased risk for early death when compared to patients in more developed countries, most commonly due to pneumonia. There was significant trend towards early diagnosis of RTT in Serbia over recent decades.

A suppressor screen in Mecp2 mutant mice implicates cholesterol metabolism in Rett syndrome.

Mutations in MECP2, encoding methyl CpG-binding protein 2, cause Rett syndrome, the most severe autism spectrum disorder. Re-expressing Mecp2 in symptomatic Mecp2-null mice markedly improves function and longevity, providing hope that therapeutic intervention is possible in humans. To identify pathways in disease pathology for therapeutic intervention, we carried out a dominant N-ethyl-N-nitrosourea (ENU) mutagenesis suppressor screen in Mecp2-null mice and isolated five suppressors that ameliorate the symptoms of Mecp2 loss. We show that a stop codon mutation in Sqle, encoding squalene epoxidase, a rate-limiting enzyme in cholesterol biosynthesis, underlies suppression in one line. Subsequently, we also show that lipid metabolism is perturbed in the brains and livers of Mecp2-null male mice. Consistently, statin drugs improve systemic perturbations of lipid metabolism, alleviate motor symptoms and confer increased longevity in Mecp2 mutant mice. Our genetic screen therefore points to cholesterol homeostasis as a potential target for the treatment of patients with Rett syndrome.

Survival with Rett syndrome: comparing Rett's original sample with data from the Australian Rett Syndrome Database.

AIM: rett syndrome is a severe neurodevelopmental disorder that typically affects females. Little is known about the natural history and survival time of these females. METHOD: we compared the survival of all Austrian female participants from Rett's historical cohort (1966) with that of affected females registered in the Australian Rett Syndrome Database. The analysis included both Kaplan-Meier analysis and a log-rank test for equality of survivor functions. RESULTS: of females in the original Austrian group, three are still alive. The median age at death was 13 years 4.8 months. The probability of survival up to the age of 25 years was 21%, compared with 71% in the Australian cohort (p<0.001). We found no practical or statistically significant differences in survival between the various birth year groups within the Australian cohort. INTERPRETATION: our data indicate that survival of females with Rett syndrome has improved since the late 1960s but that there has been shown no change in survival over the last 30 years, possibly because the follow-up time has been too short.

Longevity in Rett syndrome: analysis of the North American Database.

OBJECTIVE: To determine longevity in Rett syndrome (RTT) from a large cohort. STUDY DESIGN: The North American RTT Database allows the examination of longevity in a large cohort of individuals with RTT from the United States and Canada. This database contains information on 1928 individuals, 85.5% with typical RTT, 13.4% with atypical RTT, and 1.1% with a mutation in the methyl-CpG-binding protein 2 gene (MECP2) but not RTT. Kaplan-Meier analyses were performed to assess longevity. RESULTS: Earlier decennial cohorts exhibited better survival than recent cohorts, with most participants surviving into middle age. Comparing overall survival in persons with typical RTT and atypical RTT revealed greater mortality in typical RTT across the observed lifespan (P < .0001). Comparing survival in persons with RTT and identified MECP2 mutations and persons with unknown MECP2 status demonstrated greater mortality in the latter group (P < .0001, log-rank test). CONCLUSIONS: This analysis provides strong evidence for significant longevity in RTT and indicates the need for careful planning for long-term care of these women. The disproportionately greater survival seen in earlier time periods and in persons with atypical RTT may be attributed to more severely affected individuals dying before diagnosis in the former and to greater numbers with milder variants (ie, preserved speech and delayed onset) in the latter.

Early determinants of fractures in Rett syndrome.

OBJECTIVES: The goals were to compare the fracture incidence in Rett syndrome with that in the general population and to investigate the impact of genotype, epilepsy, and early motor skills on subsequent fracture incidence in girls and young women with Rett syndrome. METHODS: The Australian Rett syndrome study, a population-based study operating since 1993, investigated Australian subjects with Rett syndrome born since 1976. The 234 (81.2%) of 288 verified cases in the Australian Rett syndrome database in 2004 whose families had completed follow-up questionnaires and provided information about fracture history were included in the analyses. The main outcomes were fracture incidence in the Rett syndrome population and fracture risk according to genotype, presence of epilepsy, and early motor profile. RESULTS: Fracture incidence in this cohort was 43.3 episodes per 1000 person-years, nearly 4 times greater than the population rate. Risk was increased specifically in cases with p.R270X mutations and in cases with p.R168X mutations. Having epilepsy also increased fracture risk, even after adjustment for genotype. CONCLUSIONS: Girls and young women with Rett syndrome are at increased risk of fracture. Those with mutations found previously to be more severe and those with epilepsy have an increased propensity toward fractures. Improved understanding of the risk factors for fracture could contribute to better targeting of interventions to decrease fracture incidence in this vulnerable population.

Partial rescue of MeCP2 deficiency by postnatal activation of MeCP2.

In humans, mutations in the X-linked MECP2 gene, are the cause of Rett syndrome (RTT), a neurodevelopmental disorder that affects mainly girls. MeCP2 binds to methylated CpGs and is thought to act as a transcriptional repressor. In male mice, deletion or targeted mutation of Mecp2 leads to lethality and causes a neuronal phenotype. Selective mutation of Mecp2 in postnatal neurons results in a similar, although delayed, phenotype, suggesting that the symptoms are caused by MeCP2 deficiency in postmitotic neurons. In agreement with this idea, expression of a Mecp2 transgene in postmitotic neurons of Mecp2-null mutant mice resulted in the phenotypical rescue of the symptoms. To assess whether postnatal activation of MeCP2 in mutant animals could also affect the progression of the disorder, we constructed a conditionally active Mecp2 "rescue transgene" that was activated between P0 and P30. The Mecp2 transgene was under the control of the CAGGS promoter and was activated by using brain specific Cre-mediated recombination. Our results indicate that postnatal, neuron-specific activation of MeCP2 as late as 2-4 weeks of age significantly prolonged the lifespan of mutant animals and delayed the onset of neurologic symptoms.

p.R270X MECP2 mutation and mortality in Rett syndrome.

Among cases in the Australian Rett Syndrome Database, the nonsense mutation p.R270X is one of the most commonly occurring single pathogenic MECP2 mutations. In two recent published reports of the MECP2 mutational spectrum the p.R270X appeared to be under represented. We hypothesised that increased mortality arising from this mutation may underlie this apparent discrepancy. We investigated our hypothesis in two independent study groups from Australia and the UK with prospective data collections (total n=524). Only females with Rett syndrome and an identified MECP2 mutation were included. Significant differences in survival were detected among Rett syndrome cases grouped for the eight most frequent mutations (log-rank chi(2) (7)=15.71, P=0.03). Moreover, survival among cases with p.R270X, when compared with survival among cases with all the other mutations was reduced (log-rank chi(2) (2)=6.94, P=0.01). Our observation of a reduced survival associated with the p.R270X mutation offers an explanation for the under representation of p.R270X in older subjects with Rett syndrome.

Three decades of sociomedical experiences from West Swedish Rett females 4-60 years of age.

Rett syndrome, today known as a worldwide important cause behind severe mental retardation in females, has been seen in Sweden since the 1960s (the senior author). This study gives population representative clinical and sociomedical follow-up data from West Sweden (1/4 of the population in Sweden). The series comprises 54 females diagnosed in 1971-1998, 5-60 years old, median age 20. Mortality in 1971-2000 was 18% (10/54), median age at death 20. Death usually had been sudden and unexpected. The sociomedical follow-up emphasized the adult group. The large majority had usually moved to small group homes, a good and well-accepted environment once the staff had learned the particularities of these so uniquely neurodevelopmentally disabled women.

Rett syndrome: update of a 25 year follow-up investigation in Western Sweden--sociomedical aspects.

Through 1998-1999 the Swedish research team have systematically mapped 45 of 54 females with Rett syndrome (RS) aged 5-57 years (Berg M. Uppföljning av flickor med Rett syndrom i Västsverige. Socialmedicinsk kartläggning, Stencilerad rapport, Sahlgrenska universitetssjukhuset, Göteborg, 1999; Läkartidningen (Swedish Medical Journal) 96 (1999) 5488). The emphasis is on the RS females' adjustment to grown-up living. At an adult age the large majority moved over to a Swedish type of small group home. We visited these girls in their group homes and got information about their adaptation to this special home situation. We noted their behaviour and contact with the staff and interviewed their parents. The results showed that the young women usually had adjusted well. The adjustment seemed to depend on the degree of planning before the girls moved from their parents to special group homes. These seem to provide a good environment for the RS females, in respect of both physical and social aspects. Although neuropaediatrics in Sweden today has advanced in RS knowledge, the result from this research shows that in Swedish society there is still a great ignorance of RS, even among medical professionals. In particular there is a gap of knowledge when the medical responsibility had to be transferred over to adult medicine. Many of the parents emphasized the great importance of how they were listened to by professionals in public medical and social services. It is essential that professionals always listen to information from parents and personal assistants.

Epilepsy in a representative series of Rett syndrome.

UNLABELLED: In a representative series of 53 females with Rett syndrome (RS), aged 5-55 y, a history of epilepsy was present in 50 (94%), 45 of whom had 5-y active epilepsy. Compared with severe mental retardation in general, the median age of seizure onset was significantly later (4 vs 0.8 y) and partial complex seizures were more frequent (54% vs 23%). Neonatal seizures had occurred in only one and infantile spasms in none compared with 26% and 12%. After teenage, the severity of epilepsy tended to decrease, i.e. lower seizure frequency and relatively more partial seizures. The rate of being seizure-free for 1 y was 8% after 10 y and 40% after 27 y of epilepsy duration. Frequent seizures were associated with smaller head circumference. CONCLUSION: This epilepsy profile could fit in with present-day knowledge of RS as a form of dendrito-synaptogenic developmental failure with mainly late postnatal consequences, as well as being a relatively stationary condition in adulthood.

Patterns of pregnancy loss, perinatal mortality, and postneonatal childhood deaths in families of girls with Rett syndrome.

Rett syndrome is a neurodevelopmental disorder that occurs predominantly in girls and results in severe physical and intellectual handicap. A popular genetic mechanism is an X-linked dominant disorder, lethal in males. A case control study design was used to investigate fetal wastage as indicated by reported miscarriage and stillbirth prevalence, and the prevalence and cause of reported neonatal and other childhood deaths. There was no disturbance in the sibling sex ratio when case and control families were compared. In the parental generation and in the proband generation miscarriages were reported in similar proportions in case and control families. The reported stillbirth rates in case families was almost double that in control families and reported perinatal loss was more common on the maternal side in case families than in control families. Stillbirths and neonatal deaths affected slightly more boys in the parental and proband generations of case families (19 of 30) than in control families (10 of 21). Childhood deaths also occurred a little more commonly in Rett syndrome families. Sudden infant death syndrome was reported in three siblings of Rett syndrome probands but in no control siblings. Confirmation of this pattern of perinatal loss and infant mortality could indicate an alternative expression of the Rett syndrome gene.

Reduced heart rate variability in patients affected with Rett syndrome. A possible explanation for sudden death.

Incidence of sudden death in Rett syndrome is greater than that of the general population and cardiac electrical instability is a prime suspect cause. Our study shows that girls with Rett syndrome had significantly lower heart rate variability (marker of autonomic disarray) and longer corrected QT intervals compared with an age-matched group of healthy girls. These abnormalities increased with advancing stages of the syndrome. These findings suggest a possible role of cardiac dysfunction in the sudden death associated with Rett syndrome.

[Rett syndrome--an odd handicap affecting girls. A current 25-year follow-up in Western Sweden]. / Retts syndrom--ett egenartat handikapp som drabbar flickor. Aktuell västsvensk uppföljning genom 25 år.

Rett syndrome, a complicated neurodevelopmental disorder exclusively affecting girls in early childhood, is now known to be one of the major worldwide causes of severe mental retardation in females. Although internationally unknown until the mid-1980s, under another designation it had been observed in Sweden since the early 1960s. The article consists in a review of current clinical, neurobiological and genetic knowledge of the syndrome, and a systematic penetration of data collected from the follow-up of a west Swedish series of 54 female patients, 5-57 years of age. Mortality in the series was 17 percent, with a median age at death of 24 years. In most cases death was sudden and unexpected.