DNAI2 Mutations Cause Primary Ciliary Dyskinesia with Defects in the Outer Dynein Arm

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous disorder characterized by chronic destructive airway disease and randomization of left/right body asymmetry. Males often have reduced fertility due to impaired sperm tail function. The complex PCD phenotype results from dysfunction of cilia of the airways and the embryonic node and the structurally related motile sperm flagella. This is associated with underlying ultrastructural defects that frequently involve the outer dynein arm (ODA) complexes that generate cilia and flagella movement. Applying a positional and functional candidate-gene approach, we identified homozygous loss-of-function DNAI2 mutations (IVS11+1G > A) in four individuals from a family with PCD and ODA defects. Further mutational screening of 105 unrelated PCD families detected two distinct homozygous mutations, including a nonsense (c.787C > T) and a splicing mutation (IVS3-3T > G) resulting in out-of-frame transcripts. Analysis of protein expression of the ODA intermediate chain DNAI2 showed sublocalization throughout respiratory cilia. Electron microscopy showed that mutant respiratory cells from these patients lacked DNAI2 protein expression and exhibited ODA defects. High-resolution immunofluorescence imaging demonstrated absence of the ODA heavy chains DNAH5 and DNAH9 from all DNAI2 mutant ciliary axonemes. In addition, we demonstrated complete or distal absence of DNAI2 from ciliary axonemes in respiratory cells of patients with mutations in genes encoding the ODA chains DNAH5 and DNAI1, respectively. Thus, DNAI2 and DNAH5 mutations affect assembly of proximal and distal ODA complexes, whereas DNAI1 mutations mainly disrupt assembly of proximal ODA complexes

DNAI2 mutations can cause primary ciliary dyskinesia with outer dynein arm defects.

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous disorder characterized by recurrent infections of the airways and randomization of left/right body asymmetry. The phenotype results from dysfunction of motile cilia of the respiratory epithelium and the embryonic node. Dysmotile sperm tails often cause infertility in male PCD patients. Underlying ultrastructural defects frequently involve outer dynein arms (ODA), which are responsible for generation of cilia movement. We recently showed that recessive mutations of DNAH5 encoding a heavy dynein chain are frequently found in PCD with ODA defects. Genes (DNAI1, TXNDC3, DNAH11) encoding for other ODA components can also account for PCD. Here, we analyzed the protein expression of the ODA intermediate chain DNAI2 and found sub-localization throughout respiratory cilia and sperm tails. Mutational screening of 105 PCD families revealed in one affected a homozygous mutation within the facultative splice acceptor site of exon 4. RNA studies confirmed absence of exon 4 in all transcripts predicting a premature stop codon. Consistently mutant respiratory cells lacked DNAI2 expression and exhibited ODA defects by electron microscopy. High-resolution immunofluorescence imaging demonstrated mis-localization of DNAH5 indicating that DNAI2 is essential for assembly of these ODA components. In addition we report homozygous loss-of-function DNAI2 mutations located within the obligatory splice donor site of exon 11 in four affected individuals with ODA defects originating from a consanguineous PCD family that showed significant linkage to the DNAI2 locus in a total genome scan. In summary, we provide the first evidence that DNAI2 can account for PCD with ODA defects