RSPH4A and primary ciliary dyskinesia: To date, PCD-causing mutations have been found in twelve genes, encoding proteins involved in the ciliary ultrastructure (DNAH11, DNAI2, DNAL1, TXNDC3, RSPH9, RSPH4A, CCDC39, CCDC40) or assembly (KTU, LRRC50) [8]–[26]; mutations in RPGR and OFD1 have been reported in rare syndromic forms of PCD [27]–[30].