Is Rett syndrome a subtype of pervasive developmental disorders?

Rett syndrome in adults with severe intellectual disability: Exploration of behavioral characteristics

Rett syndrome is a genetically linked form of autism spectrum disorder (ASD) accompanied by intellectual disability (ID). The disorder is also characterized by cardiorespiratory dysregulation, disturbance in muscle tone, reduced brain growth and scoliosis. Over 300 studies have been published on the disorder, most of which has focused on identification of causative factors, which appears to be the result of mutations of gene MECP2. Rarely have adults with Rett syndrome been studied, and behavioral characteristics in these individuals are largely unknown. The present study aimed to extend what little is known about behavioral characteristics of Rett syndrome in adults, with particular emphasis on social, communicative, and adaptive behavior. Rett syndrome adults with severe ID were matched to autistic adults with ID and ID only controls. The implications of these data for more fully describing and diagnosing the condition in adults are discussed.

The relationship of Rett syndrome and MECP2 disorders to autism

Rett syndrome (RTT, MIM#312750) is a neurodevelopmental disorder that is classified as an autism spectrum disorder. Clinically, RTT is characterized by psychomotor regression with loss of volitional hand use and spoken language, the development of repetitive hand stereotypies, and gait impairment. The majority of people with RTT have mutations in Methyl-CpG-binding Protein 2 (MECP2), a transcriptional regulator. Interestingly, alterations in the function of the protein product produced by MECP2, MeCP2, have been identified in a number of other clinical conditions. The many clinical features found in RTT and the various clinical problems that result from alteration in MeCP2 function have led to the belief that understanding RTT will provide insight into a number of other neurological disorders. Excitingly, RTT is reversible in a mouse model, providing inspiration and hope that such a goal may be achieved for RTT and potentially for many neurodevelopmental disorders.

Hand stereotypies distinguish Rett syndrome from autism disorder

BACKGROUND

Rett syndrome (RTT) and autism disorder (AD) are 2 neurodevelopmental disorders of early life that share phenotypic features, one being hand stereotypies. Distinguishing RTT from AD often represents a challenge, and given their distinct long-term prognoses, this issue may have far-reaching implications. With the advances in genetic testing, the contribution of clinical manifestations in distinguishing RTT from AD has been overlooked.

METHODS

A comparison of hand stereotypies in 20 children with RTT and 20 with AD was performed using detailed analyses of videotaped standardized observations.

RESULTS

Striking differences are observed between RTT and AD children. In RTT, hand stereotypies are predominantly complex, continuous, localized to the body midline, and involving mouthing. Conversely, in AD children, hand stereotypies are simple, bilateral, intermittent, and often involving objects.

CONCLUSIONS

These results provide important clinical signs useful to the differential diagnosis of RTT versus AD, especially when genetic testing for RTT is not an option.

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.

Recognizing and treating Rett syndrome in schools

A review of the literature on Rett syndrome (RS) for school-based professionals is presented from a behavioral perspective. A description of RS is provided, including distinctive physical, behavioral, and emotional features, diagnostic criteria for classic and formes frustes forms of RS, and stages of the disorder. The similarities and differences between RS and autism are reviewed. Controversies regarding the classification of RS are presented, including whether RS should be classified as a neurological or psychiatric condition and whether RS should remain classified as a pervasive developmental disorder. Last, a variety of options for the treatment of RS are discussed.

Autistic disorder symptoms in Rett syndrome

According to the major classification systems it is not possible to diagnose a comorbid autistic disorder in persons with Rett syndrome. However, this is a controversial issue, and given the level of functioning of persons with Rett syndrome, the autistic disorder is expected to be present in a comparable proportion as in people with the same level of functioning. To investigate, parents of 52 females with classical and atypical Rett syndrome (2.4-49.3 years) completed the Developmental Behavior Checklist (DBC), the Diagnostic Interview for Social and Communication Disorders (DISCO) and the Dutch Vineland Screener 0-6 (VS 0-6). All participants had a severe to profound intellectual disability (ID) according to the VS 0-6. Behavior indicated an autistic disorder in 42 (DBC) to 58 percent (DISCO) of the Rett cases. Autistic behavior had decreased in 19 percent such that they no longer met the criteria for autistic disorder. Some participants were suspected of having a comorbid autistic disorder, though not more often than can be expected at their level of functioning. Clinicians should be aware of the possibility of a comorbid autistic disorder as much as they should be in other people with this level of functioning.

Autism spectrum disorders in genetic syndromes: implications for diagnosis, intervention and understanding the wider autism spectrum disorder population

BACKGROUND

An emerging literature on behavioural phenotypes has highlighted apparent associations between autism spectrum disorders (ASDs) or ASD-related phenomenology and a number of different genetically determined syndromes.

METHOD

A systematic review of the current literature regarding the association with ASD and ASD characteristics was conducted in the following syndrome groups: Fragile X, Rett, Tuberous Sclerosis Complex, Down, Angelman, CHARGE and Phenylketonuria. Specific consideration was given to the role of intellectual disability in assessing the association between ASD and these syndrome groups.

RESULTS

The review highlights that while formal diagnostic assessments may indicate an association between ASD and specific syndrome groups, detailed investigation has revealed subtle but qualitative differences in the presentation of ASD-like phenomenology in particular syndrome groups. The degree of ID of the individual clearly has a role to play with regard to the development and presentation of ASD-like characteristics, and caution should be taken when assessing ASD symptomatology in genetically determined syndromes associated with severe ID. However, degree of ID cannot solely account for the heightened prevalence of ASD characteristics in some specific syndrome groups.

CONCLUSIONS

There is a need for caution in interpreting the significance of superficial similarities between ASD and the behavioural phenotypes of certain genetically determined syndromes. However, recognition of ASD-like characteristics (even where a true diagnosis of ASD may not be relevant) in individuals with genetic syndromes is crucial in ensuring that individuals receive appropriate behavioural management and educational placement. Further research in this field requires fine-grained investigation of behavioural phenomenology within individual syndrome groups.

The diagnosis of autism in a female: could it be Rett syndrome?

The overlap between autism and Rett syndrome clinical features has led to many cases of Rett syndrome being initially diagnosed with infantile autism or as having some autistic features. Both conditions seriously disrupt social and language development and are often accompanied by repetitive, nonpurposeful stereotypic hand movements. The aims of this study were to compare the early and subsequent clinical courses of female subjects with Rett syndrome categorised by whether or not a diagnosis of autism had been proposed before Rett syndrome had been diagnosed and compare the spectrum of methyl-CpG binding protein 2 (MECP2) mutations identified among the two groups. This study made use of a total of 313 cases recorded in two databases: the Australian Rett Syndrome Database (ARSD) and the International Rett Syndrome Phenotype Database (InterRett). Cases with an initial diagnosis of autism had significantly milder Rett syndrome symptoms and were more likely to remain ambulant, to have some functional hand use and not to have developed a scoliosis. Females with the p.R306C or p.T158M mutations in the MECP2 gene were more likely to have an initial diagnosis of autism, and the specific Rett syndrome symptoms were noted at a later age. We recommend that females who are initially considered to have autism be carefully monitored for the evolution of the signs and symptoms of Rett syndrome.

Features of autism in Rett syndrome and severe mental retardation

It has long been recognized that there is phenotypic overlap between Rett syndrome (RS) and autism. Advances in our clinical and genetic understanding of RS over the past decade have made clear that the cause and course of RS and autism are distinct (except perhaps in a few cases). Despite this, further delineation of the phenotypic overlap between RS and autism is warranted to enhance clinical decision-making and to further understanding of neuropathological development in both disorders. The present study measured autistic symptoms using the Autism Behavior Checklist (ABC) in a sample of girls with RS and a comparison group of girls with severe and profound mental retardation (SMR). Controlling for developmental level and motor ability, girls with RS scored more highly than those with SMR on the Sensory and Relating subscales. In contrast, there were no group differences on the Body and Object use, Language and Social and Self-help subscales. Further work on the characterisation of the behavioral phenotype of genetic disorders such as RS and autism may aid in identifying the neuropathogenic processes that lead from gene-to-brain-to-behavior.

The autistic spectrum: subgroups, boundaries, and treatment

There is consensus about the disorders that comprise the autistic spectrum, with autistic disorder, Asperger's disorder, and PDD-NOS as the most typical examples and Rett's disorder and disintegrative disorder as the other components. Important controversies regarding the precise definitions of autistic spectrum disorders and the boundaries between the milder manifestations of those disorders, particularly PDD-NOS, and non-autistic conditions have not been and cannot be resolved fully as long as there is no known biologic cause or consistent biologic or psychological marker. This includes issues as basic as whether the autistic spectrum is a predominantly unitary entity or a collection of more or less similar phenotypes with multiple, varying etiologies. This is why the highest long-term priority in the area of definite diagnosis is the search for biologic marker(s) for autism and related autism spectrum disorders [91]. In the absence of a medical test to unequivocally diagnose autism, definitions of autism and related conditions are based only on manifestations in overt behavior, with all the unreliability this entails. In the future, the discovery of biologic correlates, causes, and pathogenetic pathways will undoubtedly change the way in which autism is diagnosed and lead to a new nosology [95]. Until that time the definitions in the current versions of the classification systems should be considered in a state of evolution. The key problem of the current classification systems is the fact that the boundaries between the various disorders are fuzzy. Instead of a categorical approach, a more useful description might be that of "autistic spectrum disorder," which reflects the range of severity of symptoms. Such a dimensional understanding of PDD is useful to clinicians, who may otherwise use nonspecific terms to avoid the categorical diagnosis of autism [31]. Rutter and Schopler [96] argued for separate clinical and research schemes because clinical and research needs are different. For research purposes it is desirable to have as much direct comparability across studies as possible. The focus is on a high degree of homogeneity within diagnostic groupings. A price must be paid for this detailed specification, and the main cost lies in the proportion of cases left undiagnosed. For example, there may be good scientific reasons for a narrowly defined categorical diagnosis that includes only individuals who definitely and clearly have a specifically defined condition and excludes individuals who may have the condition. For clinicians and educators, classification helps guide the selection of treatments for an individual. From this point of view, broader diagnostic concepts may be most appropriate [95].

The screening and diagnosis of autistic spectrum disorders

The Child Neurology Society and American Academy of Neurology recently proposed to formulate Practice Parameters for the Diagnosis and Evaluation of Autism for their memberships. This endeavor was expanded to include representatives from nine professional organizations and four parent organizations, with liaisons from the National Institutes of Health. This document was written by this multidisciplinary Consensus Panel after systematic analysis of over 2,500 relevant scientific articles in the literature. The Panel concluded that appropriate diagnosis of autism requires a dual-level approach: (a) routine developmental surveillance, and (b) diagnosis and evaluation of autism. Specific detailed recommendations for each level have been established in this document, which are intended to improve the rate of early suspicion and diagnosis of, and therefore early intervention for, autism.

Genetics of autism: overview and new directions

Genetic epidemiology is the study of inherited factors involved in the etiology of a disease or disorder and uses the methods of both medical genetics and clinical epidemiology. In general, genetic epidemiology tries to answer the following four questions: Is the disorder inherited; What phenotype is inherited; How is it inherited or what is the mode of transmission; and What is the nature of the genetic mutation, if any, that gives rise to the disorder? The hope is that by identifying the gene or genes involved in pathophysiology, a much better understanding of the steps from gene product to phenotype will be possible, leading to improvements in diagnosis, an opportunity for thoughtful family planning, and perhaps, most important, to the development of treatments based on an understanding of the biochemistry of the disorder. We review the current knowledge of the genetic epidemiology of autism and the other pervasive developmental disorders (PDDs) and highlight promising new directions. There seems to be widespread agreement that the PDDs are caused, at least in part, by genetic factors. There is also some agreement on the phenotypic boundaries associated with these same genetic factors. However, many points of uncertainty remain, and several methodologic issues need to be resolved before further progress in mapping susceptibility genes is possible. We do not specifically review molecular studies, medical conditions associated with autism, or the broader autism phenotype, as these topics are covered in other papers in this special issue.

Changing criteria of autistic disorders: a comparison of the ICD-10 research criteria and DSM-IV with DSM-III-R, CARS, and ABC

Revised versions of diagnostic manuals, the International Classification of Diseases (ICD-10), and the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) all operate with several subgroups in the autistic spectrum. Five of the subgroups are identical in the two manuals, but ICD-10 contains five in addition. 132 children were diagnosed using ICD-10, DSM-IV, DSM-III-R, the Childhood Autism Rating Scale (CARS), and the Autistic Behavior Checklist (ABC). Five out of ten alternative subgroups of Pervasive Developmental Disorders (PDD) were identified in a population of developmentally impaired children. These subgroups were the same in the two manuals; the additional ones in ICD-10 were not identified. With the exception of the groups Disintegrative Disorder and Rett syndrome, significant differences were found between all the subgroups within the PDD spectrum and between the PDD group and the non-PDD group. Some problems connected with the guidelines in the ICD-10 manual are discussed.

Early communication development in children with Rett syndrome

This retrospective pilot study investigated the course of pre-linguistic and linguistic communication development in children with Rett syndrome (RS) from birth to 24 months of age. Parents of 17 children with RS completed a questionnaire based on the Clinical Linguistic Auditory Milestone Scale. No child exceeded single word use and most children had begun to regress. Pre-regression delay was in evidence along with limited intentional gestural communication as a precursor to single word use. Limited use of communicative gestures is suggested as a possible early predictor of RS pending further investigation.

Autism research: prospects and priorities

Research prospects and priorities in the field of autism are discussed with respect to (a) diagnosis, classification, and epidemiology; (b) clinical research; (c) neuropsychological research; (d) genetics; (e) structural and functional brain imaging; (f) postmortem studies; (g) other biological research; and (h) treatment research. Also, it is argued that research into autism has a priority in the broader field of developmental psychopathology because it carries the promise of throwing light on casual mechanisms that apply beyond the syndrome of autism.

Childhood disintegrative disorder: results of the DSM-IV autism field trial

OBJECTIVE

This report is concerned with the classification of children in whom an "autistic-like" syndrome develops after some years of normal development. In DSM-IV the term "childhood disintegrative disorder" (CDD) is used to describe such cases.

METHOD

Data collected as part of the international, multisite DSM-IV field trial for autism and related conditions were examined and cases that met DSM-IV criteria for CDD were identified.

RESULTS

In 16 cases the clinician had given a CDD diagnosis; in an additional 10 cases criteria for the condition were met even though this diagnosis was not given by the clinician rating the case.

CONCLUSIONS

The available data suggest that CDD cases can be differentiated from those with autism; these two groups appear to differ in important ways. The identification of cases of CDD may be of particular importance for research.

Autism Diagnostic Interview-Revised: a revised version of a diagnostic interview for caregivers of individuals with possible pervasive developmental disorders

Describes the Autism Diagnostic Interview-Revised (ADI-R), a revision of the Autism Diagnostic Interview, a semistructured, investigator-based interview for caregivers of children and adults for whom autism or pervasive developmental disorders is a possible diagnosis. The revised interview has been reorganized, shortened, modified to be appropriate for children with mental ages from about 18 months into adulthood and linked to ICD-10 and DSM-IV criteria. Psychometric data are presented for a sample of preschool children.

The validity of autistic spectrum disorders: a literature review

The objective of this literature review is to assess the validity of autistic spectrum disorders (ASD). Twenty papers were identified that adequately investigated the internal or external validity of various subtypes of ASD. At least three groups can be distinguished from autism on clinical grounds; an Asperger syndrome subtype, and two atypical subtypes characterized by low IQ and high IQ. However, the evidence that these clinical distinctions carry inferences with respect to etiology, clinical course, and treatment is only suggestive. Nevertheless, the specification of several ASD subtypes might promote further research and resolve many of the nosologic issues with respect to the classification of pervasive developmental disorders (PDDs).

Childhood disintegrative disorder: issues for DSM-IV

Childhood disintegrative disorder, also known as Heller syndrome or as disintegrative psychosis, is a relatively uncommon condition which has variably been included in official diagnostic systems. Available evidence regarding the validity of this diagnostic concept, particularly with regard to autism, supports inclusion of the category in DSM-IV. Proposed criteria and narrative description for the disorder are presented.

Classification of pervasive developmental disorders: some concepts and practical considerations

Classifications have to meet a variety of purposes. Clinical and research needs are different and there is much to be said for separate clinical and research schemes. Care is needed to ensure that classifications provide an appropriate medium for teaching about diagnosis and do not cause difficulties when used as a "passport" to resources. Principles of classification are considered in relation to the need to take course, as well as symptomatology, into account, and with respect to the neuropsychiatric interface. The value of a multiaxial approach is noted. The pros and cons of autism and pervasive developmental disorders (PDD) as an overall descriptive term, of lumping or splitting, and of different choices with respect to PDD subcategories are discussed.