Prevalence of Autism among Adolescents with Intellectual Disabilities

Abstract

Objective: To estimate the prevalence of autism in an epidemiologically-derived population of adolescents with intellectual disabilities (ID). Method:The prevalence of autism was examined using the Autism Diagnostic Interview-Revised, with appropriate care taken in assessing lower functioning individuals and those with additional physical and sensory impairments. Individual assessment during psychological evaluation, and consensus classification of complex cases, involving clinicians experienced in the assessment of autism, contributed to the identification of autism.Results: Overall, 28% of individuals, or 2.0 of the 7.1/1000 with ID in the target population (as we have previously identified in another study), were identified with autism. Autism rates did not differ significantly across severe ID (32.0%) and mild ID (24.1%); males predominated (2.3 males to 1 female), but less so for severe ID (2 males to 1 female, compared with 2.8 males to 1 female for mild ID). Socioeconomic status did not distinguish the groups with and without autism. Less than one-half of the adolescents who met diagnostic criteria for autism were previously diagnosed as such. Conclusions:Our overall prevalence estimate for autism is in the higher range of estimates reported in previous studies of ID (more so for mild ID). This likely reflects the changes in diagnostic criteria for autism that have subsequently occurred. Discussion focuses on the identification of autism in the population with ID, and on the implications for service delivery and clinical training. Can J Psychiatry 2008;53(7):449-459Clinical Implications · Autism is a common coexisting condition in the population with ID. · The condition may remain unrecognized and (or) the symptoms of autism misattributed to other circumstances such as psychiatric disorder. · Services for individuals with ID need to recognize, and adequately support, those with coexisting autism. Limitations· An observational measure standardized specifically for the assessment of autism (for example, the Autism Diagnostic Observation Schedule) was not included. · Identifying the severity of the social-communicative impairment in individuals with ID, rather than identifying those who meet criteria for autism, is likely to have more practical relevance for identification of needs and service planning. · The relatively low prevalence rate for mild ID might have contributed to the higher prevalence rate for autism in this study, although our autism rates for mild, relative to severe, ID are consistent with those derived from recent general population surveys.

Long-Term Memory Deficits are Associated with Elevated Synaptic ERK1/2 Activation and Reversed by mGluR5 Antagonism in an Animal Model of Autism

“…Importantly, these mice exhibit behaviors that align with the three diagnostic criteria for autism (McFarlane et al, 2008;Scattoni et al, 2011). Although intellectual disability is not a DSMIV-specified criterion, its prevalence in autism is not trivial (Baio, 2012;Bryson et al, 2008;Fombonne, 2006;La Malfa et al, 2004). Our studies of hippocampus-dependent OLM in the BTBR strain determined that two-thirds of these mice exhibited marked impairments in OLM, whereas the remaining third performed at the levels of B6 mice.…”

“…A significant proportion of persons diagnosed with autism exhibit intellectual disability, yet no effective treatment exists for these cognitive impairments (Baio, 2012;Bryson et al, 2008;Fombonne, 2006;La Malfa et al, 2004). The complex phenotypes of autism are difficult to model in mice (Moy et al, 2006;Patterson, 2011;Silverman et al, 2010b), thereby slowing the development of successful therapies.…”

The Use of Next-Generation Sequencing for Research and Diagnostics for Intellectual Disability

“…This is particularly relevant for autism spectrum disorders (ASDs), as estimates of comorbidity are high. 28% of ID individuals may meet criteria for ASD (Bryson et al 2008). Estimates of ASD individuals with some degree of ID are frequently in the range of 40% -70% (71% [Chakrabarti and Fombonne 2001], 63% [Bertrand et al 2001], 40% [Baird et al 2006], and 50% [Charman et al 2011]).…”

Psychiatric Conditions and Behavioural Problems in Adolescents with Intellectual Disabilities: Correlates with Autism

“…Further methodological details and prevalence estimate for this population are reported separately. 17 In the population-based sample of adolescents with intellectual disabilities 11 (n = 171), 41 met ADI-R criteria for autism and had a nonverbal IQ of less than 75. Each adolescent was pairwise matched on age, sex, and nonverbal IQ to a participant without autism.…”