Clinical and genetic Rett syndrome variants are defined by stable electrophysiological profiles

BACKGROUND

Rett Syndrome (RTT) is a complex neurodevelopmental disorder, frequently associated with epilepsy. Despite increasing recognition of the clinical heterogeneity of RTT and its variants (e.g Classical, Hanefeld and PSV(Preserved Speech Variant)), the link between causative mutations and observed clinical phenotypes remains unclear. Quantitative analysis of electroencephalogram (EEG) recordings may further elucidate important differences between the different clinical and genetic forms of RTT.

METHODS

Using a large cohort (n = 42) of RTT patients, we analysed the electrophysiological profiles of RTT variants (genetic and clinical) in addition to epilepsy status (no epilepsy/treatment-responsive epilepsy/treatment-resistant epilepsy). The distribution of spectral power and inter-electrode coherence measures were derived from continuous resting-state EEG recordings.

RESULTS

RTT genetic variants (MeCP2/CDLK5) were characterised by significant differences in network architecture on comparing first principal components of inter-electrode coherence across all frequency bands (p < 0.0001). Greater coherence in occipital and temporal pairs were seen in MeCP2 vs CDLK5 variants, the main drivers in between group differences. Similarly, clinical phenotypes (Classical RTT/Hanefeld/PSV) demonstrated significant differences in network architecture (p < 0.0001). Right tempero-parietal connectivity was found to differ between groups (p = 0.04), with greatest coherence in the Classical RTT phenotype. PSV demonstrated a significant difference in left-sided parieto-occipital coherence (p = 0.026). Whilst overall power decreased over time, there were no difference in asymmetry and inter-electrode coherence profiles over time. There was a significant difference in asymmetry in the overall power spectra between epilepsy groups (p = 0.04) in addition to occipital asymmetry across all frequency bands. Significant differences in network architecture were also seen across epilepsy groups (p = 0.044).

CONCLUSIONS

Genetic and clinical variants of RTT are characterised by discrete patterns of inter-electrode coherence and network architecture which remain stable over time. Further, hemispheric distribution of spectral power and measures of network dysfunction are associated with epilepsy status and treatment responsiveness. These findings support the role of discrete EEG profiles as non-invasive biomarkers in RTT and its genetic/clinical variants.

Social impairments in Rett syndrome: characteristics and relationship with clinical severity

BACKGROUND

While behavioural abnormalities are fundamental features of Rett syndrome (RTT), few studies have examined the RTT behavioural phenotype. Most of these reports have focused on autistic features, linked to the early regressive phase of the disorder, and few studies have applied standardised behavioural measures. We used a battery of standardised measures of behaviour and functioning to test the following hypotheses: (1) autistic behaviour is prominent throughout childhood in RTT; (2) autistic features are more salient in individuals with milder presentation; (3) severity of autistic behaviour is associated with a wider range of behavioural problems; and (4) specific MECP2 mutations are linked to more severe autistic behaviour.

METHODS

Eighty MECP2 mutation-positive girls with RTT (aged 1.6-14.9 years) were administered: (1) the Screen for Social Interaction (SSI), a measure of autistic behaviour suited for individuals with severe communication and motor impairment; (2) the Rett Syndrome Behaviour Questionnaire (RSBQ), covering a wide range of abnormal behaviours in RTT; (3) the Vineland Adaptive Behavior Scales (VABS); and (4) a modified version of the Rett Syndrome Severity Scale (RSSS). Regression analyses examined the predictive value of age and RSSS on autistic behaviour and other behavioural abnormalities. T-tests further characterised the behavioural phenotype of individual MECP2 mutations.

RESULTS

While age had no significant effect on SSI or RSBQ total scores in RTT, VABS Socialization and Composite scores decreased over time. Clinical severity (i.e. RSSS) also increased with age. Surprisingly, SSI performance was not related to either RSSS or VABS Composite scores. Autistic behaviour was weakly linked with the RSBQ Hand behaviour factor scores, but not with the RSBQ Fear/Anxiety factor. Clinical (neurological) severity did not predict RSBQ scores, as evidenced by the analysis of individual MECP2 mutations (e.g. p.R106W, p.R270X and p.R294X).

CONCLUSIONS

Our data suggest that in RTT, autistic behaviour persists after the period of regression. It also demonstrated that neurological and behavioural impairments, including autistic features, are relatively independent of one another. Consistent with previous reports of the RTT phenotype, individual MECP2 mutations demonstrate complex associations with autistic features. Evidence of persistent autistic behaviour throughout childhood, and of a link between hand function and social skills, has important implications not only for research on the RTT behavioural phenotype, but also for the clinical management of the disorder.

MeCP2 dysfunction in Rett syndrome and related disorders

Rett syndrome, a neurodevelopmental disorder caused by mutations in the X-linked gene encoding methyl-CpG-binding protein 2 (MeCP2), is a leading cause of mental retardation with autistic features in females. MECP2 mutations have also been identified in individuals with a variety of clinical syndromes, including mild learning-disability in females, neonatal encephalopathy in males, and psychiatric disorders, autism and X-linked mental retardation in both males and females. Furthermore, MECP2 duplications have been shown to cause a progressive postnatal neurological disorder. MeCP2 is a transcriptional repressor that binds to methylated CpG dinucleotides flanked by AT-rich segments and recruits a co-repressor complex, thereby altering chromatin structure. Subtle gene expression changes have been identified in Rett patients and mouse models; however, MeCP2 dysfunction has also been shown to cause abnormalities of RNA splicing, suggesting a complex molecular pathogenesis. Discovering which genes are misregulated in the absence of functional MeCP2 and demonstrating their role in causing neuronal dysfunction and disease manifestations are challenging but important steps for understanding the pathogenesis of Rett syndrome and related disorders.

Transtornos invasivos do desenvolvimento não-autísticos: síndrome de Rett, transtorno desintegrativo da infância e transtornos invasivos do desenvolvimento sem outra especificação

A categoria "transtorno invasivos do desenvolvimento" inclui o autismo, a síndrome de Asperger, a síndrome de Rett, o transtorno desintegrativo da infância e uma categoria residual denominada transtornos invasivos do desenvolvimento sem outra especificação. Nesta revisão, a síndrome de Rett e o transtorno desintegrativo da infância, que são categorias bem definidas, serão discutidas, assim como as categorias não tão bem definidas que foram incluídas no grupo transtornos invasivos do desenvolvimento sem outra especificação. Diferentes propostas de categorização têm sido feitas, algumas baseadas em abordagem fenomenológica descritiva, outras baseadas em outras perspectivas teóricas, tais como a neuropsicologia. As propostas atuais são apresentadas e discutidas, seguidas por avaliações críticas sobre as vantagens e desvantagens desses conceitos.

Redefining disease? The nosologic implications of molecular genetic knowledge

How will developments in genetic knowledge affect the classification of disease? Leaders in genetics have suggested that knowledge of the role of genes in disease can determine nosology. Diseases might be defined by genotype, thus avoiding the limitations of more empirical approaches to categorization. Other commentators caution against disease definitions that are detached from the look and feel of disease, and argue for an interplay between genotypic and phenotypic information. Still others attribute nosologic change to social processes. We draw on an analysis of the scientific literature, our conversations with genetics clinicians, and reviews of patient organization Web sites to offer a revised interpretation of the nosologic implications of molecular genetic knowledge. We review the recent histories of three diseases--hemophilia, Rett syndrome, and cystic fibrosis--to argue that nosologic change cannot be explained by either biologic theories of disease etiology or sociologic theories of social tendencies. Although new genetic information challenges disease classifications and is highly influential in their redesign, genetic information can be used in diverse ways to reconstruct disease categories and is not the only influence in these revisions. Ironically, genetic information is likely to play a central role in producing a new, but still empirical, classification scheme.

Natural history of Rett syndrome

Rett syndrome is a unique neurodevelopmental disorder, with onset of hypotonia, autistic tendency, and abnormalities of fine finger movements and gross movements of the arms in early infancy. Clinical features include specific age-dependent symptoms. Studies of early and late signs correlated locomotive dysfunction to language disability and stereotypy to regression of higher cortical functions. Studies of sleep parameters revealed early hypofunction of brainstem aminergic neurons and late occurrence of hypofunction of dopaminergic neurons, followed by receptor supersensitivity. The syndrome's pathophysiology suggests that early hypofunction of aminergic neurons interferes with the development of higher neuronal systems. Particular symptoms surface at different ages throughout the natural course of Rett syndrome, with regressional and static periods.

[Sixty years of autism]

The concept of autism has been broadened the last few years from 'early infantile autism' to 'an autistic spectrum'. Autism and related contact disorders are grouped together under 'pervasive developmental disorders' or 'autistic spectrum disorders'. The autistic disorder, Asperger's syndrome, pervasive developmental disorder not otherwise specified (PDD-NOS), Rett's disorder and the childhood disintegrative disorder all belong to this group. People with an autistic spectrum disorder have severe difficulties in the integration of perceived stimuli into a meaningful entity. More than two-thirds of the people with the autistic disorder (classical autism) are also mentally retarded. Although autism can still only be diagnosed at the behavioural level, there is considerable consensus regarding an underlying organic aetiology. Autism is clearly a multifactorial condition. Autism cannot be cured, but adequate intervention can significantly improve the quality of life of people with this disorder. Diagnosis and intervention are highly interrelated. In the intervention, a distinction is made between family-oriented and child-oriented strategies. Augmentative communication plays a key role in the treatment. People with autism need a lot of structure, clarity and predictability, also when they have become adults.

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.

Clinical manifestations and stages of Rett syndrome

The presentation and clinical diagnosis of Rett syndrome at various ages and stages are reviewed. In addition to the classical form, variability in phenotype between different atypical Rett forms is given. Obligatory, supportive, and differential diagnostic criteria are summarized. Long-term follow-up findings in ageing Rett women are addressed.

[Rett syndrome: retrospective and prospective study of 28 patients]

From November 1982 to May 1999, 28 children with Rett syndrome were followed-up for a medium period of 6 years and 2 months. Regression of developmental milestones started at the age between 5 and 20 months. Nineteen cases of typical Rett syndrome had uneventful pre and perinatal periods, loss of previously acquired purposeful hand skills, mental and motor regression and developed hand stereotypies; sixteen had head growth deceleration and 12 gait apraxia. Nine patients were atypical cases, 2 formes frustres, 2 congenital, 3 with early seizure onset, 1 preserved speech and 1 male. Epilepsy was present in 21 patients, predominantly partial seizures and the drug of choice was carbamazepine (15 patients). In the initial evaluation most patients were distributed on Stages II and III and on follow-up on Stages III and IV. Three children died.

Rett syndrome: clinical characteristics and recent genetic advances

PURPOSE

Rett syndrome is a neurodevelopmental disorder that occurs almost exclusively in females. In recent years there has been increased knowledge concerning the multidisciplinary management of individuals with Rett syndrome. The aim of this paper is to provide an update of the clinical phenotype, natural history and current genetic understanding of the disorder.

RESULTS/CONCLUSION

Rett syndrome is thought to be the second most common cause of severe mental retardation in females after Down syndrome. it now appears that females with RS present with a much broader phenotype than originally described. Recently, mutations in the MECP2 gene encoding X-linked methyl-CpG-binding-protein 2 have been identified in some females with Rett syndrome.

Male Rett syndrome variant: application of diagnostic criteria

Classic Rett syndrome (RS) has been described in females only. Although an X chromosome origin is probable, it has not been substantiated. It is possible, therefore, that RS could occur in males. The authors describe a male with RS and review all the reported cases involving male patients. The authors compare their patient to the other patients and examine the applicability of the classic RS diagnostic criteria to this variant. To date, nine male patients with RS have been reported. The authors describe an additional male who met seven of nine necessary criteria and six of eight supportive criteria as defined by the RS Diagnostic Criteria Work Group. When the authors applied these criteria to the other nine reported patients, many necessary inclusion criteria were not met despite the absence of exclusion criteria. The supportive criteria were even more variable and limited in many patients. In conclusion, males with RS appear to represent a heterogeneous phenotype, with clinical features that may meet many but not all of the necessary diagnostic criteria of classic RS. Less restrictive criteria are needed to include this variant, which should be considered when evaluating males with idiopathic developmental regression, autistic features, and loss of hand function.

[The clinical phenomenology of Rett's syndrome]

The work was done to facilitate the clinical diagnosis and understanding of Rett syndrome (RS) by grouping the symptoms and signs in areas of neurological disfunction. This is a retrospective, longitudinal and observational study of 30 young females whose clinical manifestations were grouped using a modified Fitzgerald et al. scale for motor and behavior evaluation of patients with RS. All patients were videotaped at least during one or several appointments during their follow-up for a period of 1 to 10 years. All patients and videotapes were reviewed independently by the three authors. We followed the clinical diagnostic criteria of classic RS, and grouped the symptoms and signs in 12 groups of clinical phenomenology that represented specific areas of central or peripheral nervous system involvement: 1) dementia syndrome (fronto-temporo-parietal and limbic dysfunction); 2) extrapyramidal syndrome (basal ganglia dysfunction); 3) respiratory function disorders (brain stem reticular system disfunction); 4) sleep disorders (reticular system and limbic dysfunction); 5) epilepsy (cortico-subcortical paroxysmal bioelectrical dysfunction); 6) lower motor neuron syndrome (neuropathic dysfunction and/or peripheral neuropathy); 7) body growth retardation; 8) tonic-postural skeletal deformities; 9) deficit of pain sensation (nociceptive deficit); 10) pseudobulbar dysfunction; 11) autonomic dysfunction and 12) others (microcephaly and bruxism). In clinical practice, we recommend the use of this grouping of symptoms and signs because it makes facilities the clinical study, definition of areas of dysfunction and diagnosis of the patient with RS.

[Diagnostic criteria of autism and Asperger's syndrome: similarities and differences]

The American Psychiatric Association's last version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; APA, 1994) identifies within pervasive developmental disorders five subgroups: (a) autistic disorder; (b) Rett's disorder; (c) childhood disintegrative disorder; (d) Asperger's disorder's and (e) pervasive developmental disorder not otherwise specified. However, the diagnosis of the different sub-groups is difficult to establish, particularly between autistic disorder and Asperger's disorder. This article exposes the diagnostic criteria of autism and Asperger's syndrome in order to illustrate the similarities and differences between the two disorders.

Lamotrigine in Rett syndrome: treatment experience from a pilot study

This open pilot study was performed to evaluate the effect of Lamotrigine (LTG) in girls with Rett syndrome (RS) regarding seizure frequency, effect on gross motor dyspraxia and safety. Twelve girls with either the classical form of RS or the milder form fruste variants were included. The effect on epilepsy was evaluated as seizure frequency, motor performance (video comparison) and safety at clinical check up. The dosage of LTG was individualized and related to concomitant anti-epileptic drugs. Two of three girls with epilepsy responded relatively well to treatment, and for one of them even bad tantrums disappeared. LTG was useful in another four girls who became happier, more alert, more able to concentrate, and improved in contacting. Only mild adverse reactions as rash and tremor were seen. It is concluded that LTG could be worth trying as an adjunct in girls with RS, being aware of possible adverse reactions and no effect at all.

The prevalence and incidence of Rett syndrome in Australia

The Australian Paediatric Surveillance Unit and the Rett Syndrome Association of Australia (a parent support group) were the main sources of ascertainment of cases of Rett syndrome (RS) aged 18 years or less in Australia. Further information was obtained from questionnaires to paediatricians and families. Cases were categorised as classical, atypical, potential or non-verifiable, using internationally recognised criteria. Capture recapture methods were used to adjust prevalence measures for missing cases, and Kaplan Meier survival analysis to estimate cumulative incidence. A total of 134 cases of RS was identified, and of those over 5 years of age, 68% were classical and 32% were atypical. The adjusted prevalence was 0.72 per 10,000 females, and the cumulative incidence was 0.96 per 10,000 females to age 12 years. The prevalence was similar to that in Sweden and Scotland, but higher than in Texas. Comparing successive birth cohorts, there was evidence to suggest that RS is being diagnosed earlier and that more cases are being diagnosed as atypical.

Rett syndrome: the Swedish Genealogic Research Project. New data and present position

Using the genealogical method on both classical and atypical cases of Rett syndrome (RS) the assumption that atypical RS are true variants of the classical or nuclear group of RS was investigated. Also common ancestry, common geographical origins, and consanguinity were investigated. The pedigrees of 96 classical and 32 atypical ("forme fruste") RS individuals were examined. None of the RS females was born to first-cousin couples, but 7.3 +/- 1.9% of the classical and 6.6 +/- 3.2% of the atypical RS females had grandparents who were consanguineous. Eleven or 34% of the atypical RS females and 49 or 51% of the classical RS females could be traced to the same small, separate "Rett area". Furthermore, no less than 6 (19%) of the atypical and 28 (29%) of the classical RS females had originated in the same homestead as another RS female examined by us. Nineteen of the explored pedigrees of RS females belonged to 8 pedigrees. The pedigrees contained a mixture of typical and atypical forms of RS indicating that many or most of the variants of RS and the classical types have a common genetic background. The data gathered suggest that transmission starts with a premutation that can result over generations in a full mutation giving rise to RS. Both the X-chromosomes and an autosome pair of chromosomes may be involved.

[Rett syndrome and autism. Early comparative evaluation for signs of autism using family movies]

Rett's syndrome progresses in 4 stages: the first signs of the disorder appear after a period of 6 to 7 months, during which development is considered to be normal. This asymptomatic period is apparently an essential criterion of the diagnosis, but some parents have reported some prodromes. In stage II of the disease (before 3 years), signs common with autism dominate the clinical picture and the diagnosis of the latter was often formulated. Our working hypothesis is that the pedopsychiatric analysis of home movies of young girls with Rett's syndrome, taken by the parents before the age of 2, may be able to show early clinical signs. The present study involved examining home movies of children subsequently diagnosed as having Rett's syndrome (n = 9) in comparison to those of autistic (n = 9) and normal (n = 9) children, using semiological evaluation tools (IBSE, BFE). The persons scoring were not advised of the diagnosis. The observations were thus situated before the disorders and/or at the time of their appearance. The study confirms the asymptomatic interval between birth and the first signs of the disease, it defines the mode of onset and shows the disturbance of certain functions such as intent and imitation, more pronounced in Rett's syndrome children between 12 and 18 months. At this age, it also enables Rett's and autistic children to be differentiated on the basis of the different involvement of the "cognition" function and unusual posture, more pronounced in these girls. It does not, however, differentiate Rett's from autism between 6 and 12 months and it is thus not surprising that at this stage the diagnosis of rett's syndrome or autism may be a source of confusion.

Feeding ability in Rett syndrome

Feeding abilities in 20 individuals with Rett syndrome aged 1 1/2 to 33 years were investigated by history and clinical assessment during a meal, followed by videofluoroscopy of feeding. All were shown to have reduced movements of the mid and posterior tongue, with premature spillover of food and liquid from the mouth into the pharynx. They also showed delayed pharyngeal swallow, but otherwise pharyngeal problems were minimal. These findings were noted to be similar to those in Parkinson's disease. Those individuals with the most general neurological impairment tended to have the worst feeding problems and were smaller and malnourished.

Rett variants: a suggested model for inclusion criteria

A model for the clinical delineation of atypical cases of Rett syndrome is presented. It is based on the presence, at age > or = 10 years, of combined clusters of at least 3 of 6 primary criteria and at least 5 of 11 supportive manifestations appearing through childhood with advancing age. The model was applied to 16 mentally retarded females, aged 11-47 years (median: 23) who were considered to manifest atypical variants of the syndrome (8 formes frustes, 6 late regression, 2 congenital variants). Two of the 16 patients had an early seizure history as the initial abnormality. In parallel, the number of supportive manifestations in a series of 41 females over 10 years of age with classic Rett syndrome are given. The differentiating power was tested on 8 patients with a chromosome-verified Angelman syndrome. It is concluded that the model applied here has the capacity to identify and distinguish Rett syndrome variants of different types, to sift out other developmental disorders in routine clinical work, and to have potential as a useful research tool.

Is Rett syndrome a subtype of pervasive developmental disorders?

The author reviews the issue on whether Rett syndrome (RS) is a subtype of pervasive developmental disorders (PDDs). More than 200 articles of RS have been published in the last 10 years. Internal and external validities of RS have been established by several independent studies. There remains the question whether RS presents clinical features that meet the total criteria for PDDs. The available data seem to support the idea of classifying RS as a subtype of PDDs in the DSM-IV.