primary ciliary dyskinesia 21 (MONDO_0014123, a Monarch Disease Ontology identifier) is any primary ciliary dyskinesia in which the cause of the disease is a mutation in the DRC1 gene. Also known as: CILD21, DRC1 primary ciliary dyskinesia, ciliary dyskinesia, primary, type 21, primary ciliary dyskinesia 21 without situs inversus, primary ciliary dyskinesia caused by mutation in DRC1, primary ciliary dyskinesia type 21.