Our data on survival, growth and ventricular volume between L1camy/−;Ccdc39wt/prh and L1camy/− rats as well as L1camwt/−;Ccdc39wt/prh and L1camwt/− rats suggest that the heterozygous level of CCDC39 or L1CAM protein expression is sufficient to maintain ependymal cilia beating or neuronal cell growth, respectively, and does not affect the XLH phenotype or primary ciliary dyskinesia phenotype. This evidence concerns the gene CCDC39 and primary ciliary dyskinesia.