Find records in other NCBI databases referenced by PMC articles

There are many Entrez links that allow you to find records in other NCBI databases, given a PMC article. For the names of these links, access the E-Info service, with db=pmc (XML or JSON) and see the list of links. For example, to find ClinVar records that are referenced from PMC2869000:

To go the other way, and find PMC articles that link to a given record in another database, you have to use the reciprocal link. Most links of the form pmc_db have a reciprocal link of the form db_pmc. The easiest way to see if the reciprocal link exists is to try it. You can check this comprehensive list of Entrez links to verify that the desired link is supported.