Project created 11th Oct 2017. This project contains files that are used in the Protocol for 'Explaining variation in neurodevelopmental outcomes in children with sex chromosome trisomies: a test of the double hit hypothesis' N.B. Many background documents are the same as those for the Twin study of laterality : see project at https://osf.io/hr6ad/ for details of ethics approvals, protocol, test details, etc. **Additions June 2018** New components have been added to hold Data and Results for this project. Please see the wiki for each component for a description. Appendix 10 contains summary results for an additional exploratory gene-based analysis added in December 2019, which is referenced in a supplementary comment to the paper in Wellcome Open Research. **Corrections May 2021** Appendix 9 had a missing page, which meant that SNPs 7-11 were omitted from the table. This has been corrected, and the script Double_hit_results.rmd has also been updated.