Participant inclusion criteria for the ASD sample were an existing clinical diagnosis of ASD according to DSM-IV [50 ], DSM-IV-TR [51 ], DSM-5 [5 ] or ICD-10 [52 ] criteria and age between 6 and 30 years. ASD diagnoses were based on a comprehensive assessment of the participant’s clinical history and/or current symptom profile, depending on when the participant was originally identified at that site. In addition, we assessed ASD symptoms using the Autism Diagnostic Observation Schedule (ADOS; [53 (
link), 54 ]) and the Autism Diagnostic Interview-Revised (ADI-R; [55 ]). However, individuals with a clinical ASD diagnosis who did not reach cut-offs on these instruments were not excluded. Clinical judgement has been found to be more stable than scores on individual diagnostic instruments alone [56 (
link)], reflecting the moderate-to-good but still imperfect accuracy of such tools [57 (
link)].
Exclusion criteria included significant hearing or visual impairments not corrected by glasses or hearing aids, a history of alcohol and/or substance abuse or dependence in the past year and the presence of any MRI contraindications (e.g. metal implants, braces, claustrophobia) or failure to give informed written consent to MRI scanning (or to provide contact details for a primary care physician at centres where this is a pre-condition for scanning). Participants were purposively sampled to enable in depth experimental characterisation of potential biomarkers (including MRI scans). Therefore, we excluded individuals with low IQ (<50) as core measures (e.g. most cognitive tasks and MRI scanning without sedation) were deemed difficult to administer in this group. Participants who did not complete an IQ assessment were excluded (controls:
n = 7, ASD:
n = 10). In the TD group, individuals who had a
T score of 70 or higher on the self-report (1 adult) or parent-report form (1 adolescent, 3 children) of the Social Responsiveness Scale [58 ] were also excluded.
In the ASD sample, psychiatric conditions (except for psychosis or bipolar disorder) were allowed as up to 70% of people with ASD have one or more psychiatric disorders [7 (
link)] and reflect DSM-5 that allows co-occurring psychiatric disorders alongside an ASD diagnosis [5 ]. In future individual biomarker analyses, additional exclusion criteria or sub-grouping may then be applied (e.g. ADI-R cut-offs, medication-free, etc.).
Exclusion criteria of the TD/ID group were the same as described above for the ASD participants with the exception that in the TD group parent- or (where appropriate) self-report of a psychiatric disorder was also an exclusion criteria.
Charman T., Loth E., Tillmann J., Crawley D., Wooldridge C., Goyard D., Ahmad J., Auyeung B., Ambrosino S., Banaschewski T., Baron-Cohen S., Baumeister S., Beckmann C., Bölte S., Bourgeron T., Bours C., Brammer M., Brandeis D., Brogna C., de Bruijn Y., Chakrabarti B., Cornelissen I., Acqua F.D., Dumas G., Durston S., Ecker C., Faulkner J., Frouin V., Garcés P., Ham L., Hayward H., Hipp J., Holt R.J., Isaksson J., Johnson M.H., Jones E.J., Kundu P., Lai M.C., D’ardhuy X.L., Lombardo M.V., Lythgoe D.J., Mandl R., Mason L., Meyer-Lindenberg A., Moessnang C., Mueller N., O’Dwyer L., Oldehinkel M., Oranje B., Pandina G., Persico A.M., Ruggeri B., Ruigrok A.N., Sabet J., Sacco R., Cáceres A.S., Simonoff E., Toro R., Tost H., Waldman J., Williams S.C., Zwiers M.P., Spooren W., Murphy D.G, & Buitelaar J.K. (2017). The EU-AIMS Longitudinal European Autism Project (LEAP): clinical characterisation. Molecular Autism, 8, 27.