ObjectiveReports of rising prevalence of autism spectrum disorders (ASD), along with their profound personal and societal burden, emphasize the need of methodologically sound studies to explore their causes and consequences. We here present the design of a large intergenerational resource for ASD research, along with population-based prevalence estimates of ASD and their diagnostic validity.MethodThe Stockholm Youth Cohort is a record-linkage study comprising all individuals aged 0–17 years, ever resident in Stockholm County in 2001–2007 (N = 589,114). ASD cases (N = 5,100) were identified using a multisource approach, involving registers covering all pathways to ASD diagnosis and care, and categorized according to co-morbid intellectual disability. Prospectively recorded information on potential determinants and consequences of ASD were retrieved from national and regional health and administrative registers. Case ascertainment was validated through case-note review, and cross validation with co-existing cases in a national twin study.ResultsThe 2007 year prevalence of ASD in all children and young people was 11.5 per 1,000 (95% confidence interval 11.2–11.8), with a co-morbid intellectual disability recorded in 42.6% (41.0–44.2) of cases. We found 96.0% (92.0–98.4) of reviewed case-notes being consistent with a diagnosis of ASD, and confirmed ASD in 85.2% (66.2–95.8) of affected twins.ConclusionsFindings from this contemporary study accords with recently reported prevalence estimates from Western countries at around 1%, based on valid case ascertainment. The Stockholm Youth Cohort, in light of the availability of extensive information from Sweden's registers, constitutes an important resource for ASD research. On-going work, including collection of biological samples, will enrich the study further.

The systematic review identified 41 eligible studies. All were published after the year 2000 and 21 originated in Europe. The majority examined QoL in neurodevelopmental disorders, including attention-deficit hyperactivity disorder (k = 17), autism spectrum disorder (k = 6), motor disorders (k = 5) and intellectual disability (k = 4). Despite substantial heterogeneity, studies demonstrate that self-reported global QoL is significantly reduced compared to typical/healthy controls across several disorders and QoL dimensions. Parents' ratings were on average substantially lower, casting doubt on the validity of proxy-report. Studies for large diagnostic groups such as depressive disorders, anxiety disorders, (early onset) schizophrenia and eating disorders are largely lacking. We conclude that representative, well-characterized normative and clinical samples as well as longitudinal and qualitative designs are needed to further clarify the construct of QoL, to derive measures of high ecological validity, and to examine how QoL fluctuates over time and is attributable to specific conditions or contextual factors.

Research on sex-related differences in Autism Spectrum Disorder (ASD) has been impeded by small samples. We pooled 28 datasets from 18 sites across nine European countries to examine sex differences in the ASD phenotype on the ADI-R (376 females, 1763 males) and ADOS (233 females, 1187 males). On the ADI-R, early childhood restricted and repetitive behaviours were lower in females than males, alongside comparable levels of social interaction and communication difficulties in females and males. Current ADI-R and ADOS scores showed no sex differences for ASD severity. There were lower socio-communicative symptoms in older compared to younger individuals. This large European ASD sample adds to the literature on sex and age variations of ASD symptomatology.Electronic supplementary materialThe online version of this article (10.1007/s10803-018-3510-4) contains supplementary material, which is available to authorized users.