Therefore, we investigated the localization of the DNALI1-associated dynein heavy chains DNAH1 and DNAH7 and the CETN2-associated heavy chain DNAH6 in the ciliary axoneme of respiratory cells from PCD individuals with bi-allelic disease-causing variants in CCDC39 or CCDC40. The gene discussed is CCDC40; the disease is primary ciliary dyskinesia.