Rett syndrome: review and discussion of current diagnostic criteria

Autism sensory dysfunction in an evolutionarily conserved system

There is increasing evidence for a strong genetic basis for autism, with many genetic models being developed in an attempt to replicate autistic symptoms in animals. However, current animal behaviour paradigms rarely match the social and cognitive behaviours exhibited by autistic individuals. Here, we instead assay another functional domain—sensory processing—known to be affected in autism to test a novel genetic autism model in Drosophila melanogaster. We show similar visual response alterations and a similar development trajectory in Nhe3 mutant flies (total n = 72) and in autistic human participants (total n = 154). We report a dissociation between first- and second-order electrophysiological visual responses to steady-state stimulation in adult mutant fruit flies that is strikingly similar to the response pattern in human adults with ASD as well as that of a large sample of neurotypical individuals with high numbers of autistic traits. We explain this as a genetically driven, selective signalling alteration in transient visual dynamics. In contrast to adults, autistic children show a decrease in the first-order response that is matched by the fruit fly model, suggesting that a compensatory change in processing occurs during development. Our results provide the first animal model of autism comprising a differential developmental phenotype in visual processing.

MeCP2-Related Diseases and Animal Models

The role of epigenetics in human disease has become an area of increased research interest. Collaborative efforts from scientists and clinicians have led to a better understanding of the molecular mechanisms by which epigenetic regulation is involved in the pathogenesis of many human diseases. Several neurological and non-neurological disorders are associated with mutations in genes that encode for epigenetic factors. One of the most studied proteins that impacts human disease and is associated with deregulation of epigenetic processes is Methyl CpG binding protein 2 (MeCP2). MeCP2 is an epigenetic regulator that modulates gene expression by translating epigenetic DNA methylation marks into appropriate cellular responses. In order to highlight the importance of epigenetics to development and disease, we will discuss how MeCP2 emerges as a key epigenetic player in human neurodevelopmental, neurological, and non-neurological disorders. We will review our current knowledge on MeCP2-related diseases, including Rett Syndrome, Angelman Syndrome, Fetal Alcohol Spectrum Disorder, Hirschsprung disease, and Cancer. Additionally, we will briefly discuss about the existing MeCP2 animal models that have been generated for a better understanding of how MeCP2 impacts certain human diseases.

Syndromes of disordered chromatin remodeling

Syndromes of disordered 'chromatin remodeling' are unique in medicine because they arise from a general deregulation of DNA transcription caused by mutations in genes encoding enzymes which mediate changes in chromatin structure. Chromatin is the packaged form of DNA in the eukaryotic cell. It consists almost entirely of repeating units, called nucleosomes, in which short segments of DNA are wrapped tightly around a disk-like structure comprising two subunits of each of the histone proteins H2A, H2B, H3 and H4. Histone proteins are covalently modified by a number of different adducts (i.e. acetylation and phosphorylation) that regulate the tightness of the DNA-histone interactions. Mutations in genes encoding enzymes that mediate chromatin structure can result in a loss of proper regulation of chromatin structure, which in turn can result in deregulation of gene transcription and inappropriate protein expression. In this review we present examples of representative genetic diseases that arise as a consequence of disordered chromatin remodeling. These include: alpha-thalassemia/mental retardation syndrome, X-linked (ATR-X); Rett syndrome (RS); immunodeficiency-centromeric instability-facial anomalies syndrome (ICF); Rubinstein-Taybi syndrome (RSTS); and Coffin-Lowry syndrome (CLS).

The influence of premorbid language skills and behavior on language recovery in children with verbal auditory agnosia

Previous studies of children with Landau-Kleffner syndrome and related language-epilepsy syndromes have focused on the relationship of seizure control to language recovery. We examined the effect of premorbid language skills and behavior, as well as some characteristics of clinical seizures and electroencephalograms, on language recovery in a retrospective study of 67 children with the severe receptive and expressive language disorder, verbal auditory agnosia. Fifty-eight percent of these children had seizures, 76% were autistic, and 24% had a history of language regression after showing previously normal language skills. The duration of language loss was not influenced by the persistence of clinical seizures. Premorbid language and behavior were more predictive of language recovery in these children. Most children with normal early language (acquired verbal auditory agnosia) had onset of language loss after age 3 years, in contrast to those with abnormal early language. Children with acquired verbal auditory agnosia were more likely to show fluctuations in language skills than those in other groups. Autistic children were more likely to begin having seizures before age 3 years, and had a longer duration of language loss and lower educational placement at time of last follow-up than those with normal behavior. This study emphasizes the importance of assessing premorbid language and behavior in predicting recovery of language skills in children with language-epilepsy syndromes.

A prevalence study of Rett syndrome in an institutionalized population

An institution for the mentally retarded was surveyed to determine the prevalence rate of Rett syndrome (RS). Four patients with definite RS and one with probable RS were identified in a population of 350, yielding a prevalence rate of 1 in 87, about 1% of institutionalized male and female patients with mental retardation. In this population of patients with severe and profound mental retardation (N = 297), 138 females were surveyed, suggesting a prevalence rate among females of 1 in 34 in an institutional population of persons with mental retardation. Surveys of institutions for persons with mental retardation may be an effective method to identify adults with RS.

Preliminary report on construction and validation of a pediatric sleep disturbance questionnaire

A scale to assess sleep disturbance of children with developmental disabilities is reported. The scale has been used with a small sample of 14 children diagnosed as having Tourette Disorder, 36 physically handicapped children (cerebral palsy). Also, a group of 115 nonhandicapped Native American children were surveyed to assess whether the items might be appropriate for use with such children. The scale has 6 distinct factors and appears to have adequate reliability and validity.

The hand apraxia scale

A scale for the assessment of hand apraxia was developed on a population of 239 institutionalized mentally retarded adults. Guttman scaling indicates adequate reliability and validity.

Rett syndrome and associated movement disorders

Rett syndrome, a progressive neurodegenerative disorder described only in female subjects, is manifested by a wide spectrum of behavioral and motor abnormalities. We studied 32 patients with this disorder, ages 30 months to 28 years old, and characterized their extrapyramidal disturbance. The most common motor abnormalities were stereotyped movements and gait disturbance, seen in all patients. Bruxism, oculogyric crises, parkinsonism, and dystonia were also common, but myoclonus and choreoathetosis were seen only infrequently. The hyperkinetic movement disorders tended to dominate in younger patients, while bradykinetic disorders were more evident in the older patients. This study provides evidence that movement disorders seen in Rett syndrome reflect age-related neurodegenerative changes in the basal ganglia.

Pervasive disintegrative disorder: are Rett syndrome and Heller dementia infantilis subtypes?

Children with developmental regression and emerging symptoms of autism have been given a variety of classifications. The authors compare two boys with Heller dementia with six girls with Rett syndrome. They all differed from children with classic autism in that they had normal prenatal and perinatal periods, followed by marked developmental regression, after which they acquired few or no skills. The boys differed from the girls in terms of estimated prevalence, age at onset, stereotypic breathing patterns, midline hand stereotypies, hand and gait apraxia and speech development. It is suggested that these children should be distinguished from those with classic autism, and should be classified as 'pervasive disintegrative disorder, Heller type' and 'pervasive disintegrative disorder, Rett type'.

Rett syndrome: case reports and management strategies

Rett Syndrome (RS) is a mental retardation syndrome occurring in females consisting of normal pre-, peri-, and neonatal growth and development, followed by rapid regression after 3 but before 30 months, an arrest of the regression and a developmental plateau. The regression results in autistic behavior, with loss of production and comprehension of language, seizures, hyperventilation, characteristic hand-wringing, and ataxic gait. Four case histories of RS from the authors' practice are presented. Management strategies are presented and needed research is suggested.