Release
New information obtained by dbSNP becomes available to the public periodically in a series of “builds” (i.e. revisions and releases of data). There is no schedule for releasing new builds; instead, builds are usually released when a new genome build becomes available, assuming that the genome has some cataloged variation associated with it. This occurs approximately every 1–2 months. Genome sequences often contain errors so reference SNPs (“refSNP”) from previous builds, as well as new submitted SNPs, are re-mapped to the newly available genome sequence through multiple cycles of BLAST and MegaBLAST. Multiple submitted SNPs, if mapping to the same location, are clustered into one refSNP cluster and are assigned a reference SNP ID number. However, if two refSNP cluster records are found to map to the same location (i.e. are identical), then dbSNP will also merge those records together. In this case, the smallest refSNP number ID (i.e. the earliest record) would now represent both records, and the larger refSNP number IDs would become obsolete. These obsolete refSNP number IDs and are not used again for new records. When a merger of two refSNP records occurs, the change is tracked, and the former refSNP number IDs can still be used as a search query. This process of merging identical records together reduces redundancy within dbSNP.
There are two exceptions to the above merging criteria. First, if there exists two classes of variation at one site (e.g. a SNP and a DIP), then the two refSNP number IDs are not merged. Secondly, clinically important refSNPs that have been cited in the literature are termed “precious” and are never merged so as to prevent later confusion.
Read more about this topic: Db SNP
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—Stefan Zweig (18811942)
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