DECIPHER is a web-based resource and database of genomic variation data from analysis of patient DNA. It documents submicroscopic chromosome abnormalities (microdeletions and duplications) and pathogenic sequence variants (single nucleotide variants - SNVs, Insertions, Deletions, InDels), from over 25000 patients and maps them to the human genome using Ensembl or UCSC Genome Browser. In addition it catalogues the clinical characteristics from each patient and maintains a database of microdeletion/duplication syndromes, together with links to relevant scientific reports and support groups. An acronym of DatabasE of Chromosomal Imbalance and Phenotype in Humans using Ensembl Resources, DECIPHER was initiated in 2004 at the Sanger Institute in the United Kingdom, funded by the Wellcome Trust. However it is supported by an international research consortium, with patient data contributed by more than 240 clinical genetics centres from 33 countries. Each centre is represented by an experienced clinical geneticist and a senior molecular cytogeneticist. Aims DECIPHER was established in 2004 by Nigel Carter of the Wellcome Trust Sanger Institute and Helen Firth, a clinical genetics consultant at Addenbrooke's Hospital in Cambridge. It has three main aims: Aid in the interpretation of plausibly pathogenic variants from genome- wide analyses by placing them in the context of known pathogenic variants, other plausibly pathogenic variants and population variation Annotate plausibly pathogenic variants with their likely functional impact using Ensembl tools to compare sequence and structural variants with the latest functional annotation of the current human reference genome e.g. define which genes are involved in a specific copy number variant (microdeletion / microduplication) or for sequence variants, whether they are positioned within a gene or regulatory element. Facilitate research into the study of genes that affect human health and development to improve diagnosis, management and therapy of rare diseases. As a tool for clinical geneticists, cytogeneticists and molecular biologists, DECIPHER is used to determine whether gene copy number variations identified in patients are of clinical significance. Members can visualise the genes within the region of DNA altered in their patients, and ascertain whether any are known to be implicated in disease. Chromosomal imbalances are a major cause of developmental delay, learning disabilities and congenital abnormalities and — according to Emily Niemitz writing in Nature Genetics — the database facilitates collaboration between researchers and clinicians who have patients with similar clinical characteristics, which can "assist in the discovery of new syndromes and in the recognition of genes of clinical importance."