Journal of Intellectual Disability Research     pp  –    619 ©  Blackwell Science Ltd Blackwell Science, LtdOxford, UKJIDRJournal of Intellectual Disability Research -Blackwell Science Ltd, Original ArticleBehaviour problems in Rett syndromeR. H. Mount et al. Correspondence: Richard Hastings PhD, School of Psychology, University of Wales, Bangor, Gwynedd LL AS, UK (e-mail: r.hastings@bangor.ac.uk). Behaviour problems in adult women with Rett syndrome R. H. Mount, 1 R. P. Hastings, 2 S. Reilly, 3 H. Cass 4 & T. Charman 1 1 Behavioural and Brain Sciences Unit, Institute of Child Health, University College London, London, UK 2 School of Psychology, University of Wales, Bangor, UK 3 School of Human Communication Sciences, LaTrobe University, and Murdoch Children’s Research Institute, Melbourne, Australia 4 Neurosciences Unit, Institute of Child Health, University College London, London, UK Abstract Background Despite considerable interest in the genetic, physical and neurological aspects of Rett syndrome (RS), there have been few studies of asso- ciated behavioural and emotional features. Further- more, few case studies or surveys have included adult women with RS. The main aim of the present study was to compare behaviour problems in a sample of women with RS against data from normative samples. Methods The primary carers of  women with RS completed the community version of the Aberrant Behavior Checklist. Results Women with RS were rated as having lower levels of irritability, hyperactivity and inappropriate speech behaviours than normative samples of adults with intellectual disability. Conclusions A number of factors may affect the pre- sentation of behaviour problems in women with RS (e.g. cognitive impairments or physical disabilities). Therefore, more research is needed in order to gen- erate information about the behavioural phenotype of RS. The implications of the present data for future research are also discussed. Keywords Aberrant Behavior Checklist, behaviour problems, Rett syndrome Introduction Rett syndrome (RS) is a neurological disorder with associated severe to profound intellectual disability (ID) and physical disabilities (Kerr & Engerström ). The disorder in its classic form appears to affect only females. Prevalence studies have suggested that the disorder is rare, affecting somewhere between . in   females (Terai et al. ) and . in   females (Skjeldal et al. ). Dur- ing early development, girls with RS may acquire language skills at the level of single-word utterances, fine and gross motor skills evolve, and some girls begin to walk. However, between  and  months, development slows or arrests, and this period of stag- nation is followed by a period of regression between one and  years of age (Hagberg ). During regression, a profound loss of skills is seen in the domains of social contact and communication, hand use, and language (Engerström ). The development of individuals with RS typically reaches a plateau post-regression between the ages of  and  years. Neuromotor function may con- tinue to decline, but does not necessarily do so (Engerström & Hagberg ), and some individuals with RS may develop new skills during this stage (Piazza et al. ). Post-regression, individuals with RS are profoundly cognitively impaired (Woodyatt & Ozanne , ), typically with a mental age of <  months (e.g. Perry et al. ) and ‘pre- intentional’ levels of communication (Woodyatt & Ozanne , ). Little has been written about the development of adult women with RS, but in