Around 90% of individuals with PCD have ultrastructural defects affecting protein(s) in the outer and/or inner dynein arms, which give cilia their motility, with roughly 38% of these defects caused by mutations on two genes, DNAI1 and DNAH5, both of which code for proteins found in the ciliary outer dynein arm.There is an international effort to identify genes that code for inner dynein arm proteins or proteins from other ciliary structures (radial spokes, central apparatus, etc.) associated with PCD. The role of DNAH5 in heterotaxy syndromes and left-right asymmetry is also under investigation. At least 32 genes have been implicated in this condition. Another gene associated with this condition is GAS2L2. Pathophysiology
This condition is genetically inherited. Structures that make up the cilia, including inner and/or outer dynein arms, central apparatus, radial spokes, etc. are missing or dysfunctional and thus the axoneme structure lacks the ability to move. Axonemes are the elongated structures that make up cilia and flagella. Additionally, there may be chemical defects that interfere with ciliary function in the presence of adequate structure. Whatever the underlying cause, dysfunction of the cilia begins during and impacts the embryologic phase of development. Specialised monocilia known as nodal cilia are at the heart of this problem. They lack the central-pair microtubules of ordinary motile cilia and so rotate clockwise rather than beat; in the primitive node at the anterior end of the primitive streak in the embryo, these are angled posteriorly such that they describe a D-shape rather than a circle.
DPR and NFJS syndromes were specifically found to be differentiated from other syndromes by a mutation of the keratin 14 gene, located on chromosome 17q21.2. This was found when keratin genes KRT14, KRT16, and KRT17 were reassessed in 2006, revealing pathogenic mutations of KRT14 in all patients with NFJS/DPR, displaying a strong correlation and suggesting a potential causation. The type of mutations observed were heterozygous nonsense or frameshift mutations, meaning the function of the gene was completely disrupted (missense is correlated with EBS). The different phenotypic presentations of recessive (EBS-causing) versus dominant (NFJS/DPR-causing) premature truncation mutations in KRT14 are still unclear. The NFJS/DPR mutations were verified using two screening approaches, in which it was found that 17delG was absent from a panel of 100 control individuals, and C18X and Q7X were found to create a novel recognition site for the endonucleases DdeI and BfaI. Because the mutations were found to be heterozygous, the condition was concluded to be autosomal dominant in its inheritance pattern.Interestingly, a study conducted on five families using a two-point linkage analysis of the combined genotyping data for three families across the NFJS/DPR candidate region generated an LOD score of 6.2 at marker D17S800, with a recombination score of 0. Further analysis revealed that NFJS may be caused by an identical founder mutation located within a 6-Mb interval between D17S946 and D17S2180.