Because BDC uses dbGaP permission infrastructure for controlling access to data, any additional requirements for approval (e.g., a Letter of Collaboration) are enforced. Should BDC implement novel methods for requesting and approving access, these same requirements will be enforced. Study principal investigators for studies with special requirements or especially sensitive data are encouraged to contact the BDC and NHLBI Data Access Committee (centraldac@mail.nih.gov) project office teams to discuss any concerns.