Ultrastructural analysis by TEM of respiratory ciliary axonemes from individuals carrying CCDC151 mutations showed a loss of the outer dynein arms (mean of ODAs detected: 0.8–0.9) from ciliary axonemes compared to those of unaffected control individuals (ODA mean: 7.5–9) (Figure 5C). These results are consistent with the ultrastructural ciliary phenotype of ccdc151ts272a (flanders) mutants, ccdc151 RNAi planarians, and Ccdc151Snbl mice (Figures 2H, S4E, and 3C). We further examined this defect at the molecular level by immunofluorescence staining of the respiratory cells of individuals OP-675 and OP-1255 using antibodies directed against two established markers of human dynein arm integrity, the ODA marker DNAH5 and IDA marker DNALI1 (which is a light intermediate dynein associated with some IDAs). DNAH5 was undetectable in the axonemes of CCDC151 mutant individuals, suggesting that CCDC151 deficiency likely causes a disruption of axonemal ODA assembly (Figure 5A). In contrast, DNALI1 correctly localized to the axonemes of both individuals’ respiratory cells. This marker showed a similar distribution to that of control individual’s cilia (Figure 5B), suggesting that CCDC151 mutations do not alter assembly of IDA proteins.