Dimensional phenotypic analysis and functional categorisation of mutations reveal novel genotype-phenotype associations in Rett syndrome.

We aimed to improve the understanding of genotype-phenotype correlations in Rett syndrome (RS) by adopting a novel approach to categorising phenotypic dimensions - separating typicality of presentation, outcome severity and age of onset - and by classifying MECP2 mutations strictly by predicted functional attributes. MECP2 mutation screening results were available on 190 patients with a clinical diagnosis of RS (140 cases with classic RS, 50 with atypical RS). 135 cases had identified mutations. Of the 140 patients, 116 with classic RS (82.9%) had an identified mutation compared with 19 of 50 patients (38%) with an atypical presentation. Cases with early onset of regression and seizures, and those with clinical features that might indicate alternative aetiologies, were less likely to have mutations. Individuals with late truncating mutations had a less typical presentation than cases with missense and early truncating mutations, presumably reflecting greater residual function of MECP2 protein. Individuals with early truncating mutations had a more severe outcome than cases with missense and late truncating mutations. These findings held when restricting the analysis to cases over 15 years of age and classic cases only. Previous findings of variation in severity among the common mutations were confirmed. The approach to phenotypic and genotypic classification adopted here allowed us to identify genotype-phenotype associations in RS that may aid our understanding of pathogenesis and also contribute to clinical knowledge on the impact of different types of mutations.

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.

Towards a behavioral phenotype for Rett syndrome.

Despite considerable interest in Rett syndrome, there have been few studies of associated behavioral and emotional problems. In the present study, 143 girls with Rett syndrome were compared on the Developmental Behavior Checklist with 85 girls with severe to profound mental retardation of mixed etiologies. After controlling for the effects of physical disabilities, we found that the girls with Rett syndrome presented more "autistic-relating" and fewer antisocial behaviors. A subsample of children with autism was also compared to the girls with Rett syndrome on autistic-relating behaviors, revealing that the Rett syndrome group did not present with classic autistic behavioral features The implications of these results for the identification of a Rett syndrome behavioral phenotype are discussed.

The Rett Syndrome Behaviour Questionnaire (RSBQ): refining the behavioural phenotype of Rett syndrome.

BACKGROUND: Although physical features, including loss of hand skills, deceleration of head growth, spasticity and scoliosis, are cardinal features of Rett syndrome (RS), a number of behavioural features are also associated with the disorder, including hand stereotypies, hyperventilation and breath holding. No study has tested the specificity of these behavioural features to individuals with RS, compared to individuals with severe to profound mental retardation (SMR). METHOD: A novel checklist of characteristic RS behavioural and emotional features, the Rett Syndrome Behaviour Questionnaire (RSBQ), was developed to test the type and specificity of behavioural features of RS against those found in girls with SMR. RESULTS: After controlling for the effects of RS-related physical disabilities, the RSBQ discriminated between the groups. Some aspects of the behaviours found to be specific to RS are included in the necessary or supportive RS diagnostic criteria, notably hand behaviours and breathing problems. Additional behavioural features were also more frequently reported in the RS than the SMR group, including mood fluctuations and signs of fear/anxiety, inconsolable crying and screaming at night, and repetitive mouth and tongue movements and grimacing. CONCLUSIONS: Full validation of the scale requires confirmation of its discriminatory power and reliability with independent samples of individuals with RS and SMR. Further delineation of the specific profile of behaviours seen in RS may help in identification of the function of the MECP2 gene and in improved differential diagnosis and management of individuals with RS.