Footnotes

• Contributors JNT, DRH, SRL, KMC, NG-K and WW contributed to the conception and design of the project. RCB was involved in the organisation and execution of the project, design and execution of statistical analyses, and prepared the first draft of the manuscript. JCM, CR, WW and DEG also contributed to the organisation and execution of the project. All authors were involved in the review and critique of the manuscript.

• Funding This work was supported by The Australian Research Council (Discovery Project Grant DP110103346 to KMC, JNT, NG-K, and WW); The New South Wales Institute of Psychiatry (Training Fellowship in Psychiatric Research awarded to RCB); Monash Research Fellowship and ARC Discovery Early Career Researcher Grant (DE160100042) to DRH; the Dementia Collaborative Research Centre—Assessment and Better Care, University of New South Wales as part of the Australian Government's Dementia Initiative; and the Genetics of Learning Disability (GOLD) Service. Salary for the molecular component, in part, was supported by the National Health and Medical Research Council (Project Grants 104299 and 1103389) to DEG.

• Competing interests None declared.

• Ethics approval Obtained from required Human Research Ethics Committees.

• Provenance and peer review Not commissioned; externally peer reviewed.