Although chronic lung disease is commonly associated with PCD in human patients, there are no significant histopathological defects in the lungs of mice lacking either ciliary protein Pcdp1 or Spef2, despite the presence of upper airway abnormalities, male infertility, hydrocephalus, and a decrease in ciliary motility [41,42]. This evidence concerns the gene CFAP221 and primary ciliary dyskinesia.