Participants were between the ages of 4-19, living in England or Wales, and had to meet the eligibility criteria. These criteria included: i) having an intellectual disability; ii) having had a diagnostic microarray by an accredited Regional Genetic Centre, or has had next-generation sequencing; iii) having at least one Copy Number Variant or Single Nucleotide Variant reported as pathogenic; iv) having a legal guardian available to consent and provide detailed medical and behavioural history. Participants were either in the Cardiff University Sample with longer and more detailed in-person interviews involving the whole family, or in the University College London Sample with shorter and more frequent online interviews.