DNAH9 and primary ciliary dyskinesia: Discovery of new disease genes—Four genes, i.e., TTC12 [11], GAS2L2 [12], DNAH9 [13] and DNAJB13 [14], whose mutations are responsible for Primary Ciliary Dyskinesia (PCD) have been identified through molecular and cellular studies performed in the framework of the RaDiCo-DCP cohort.