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

Abstract

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.

A 20-year experience of electron microscopy in the diagnosis of primary ciliary dyskinesia

“…Two main genes, DNAI1 and DNAH5 have been identified to date [33,34] for PCD with isolated ODA defects and the other identified genes (i.e. RPGR, TXNDC3, DNAH1, DNAI2, KTU, RSPH9 and RSPH4A) concern a few PCD families [35][36][37][38][39][40]. The identification of the ciliary ultrastructural defect by TEM analysis could also be helpful for genetic analysis.…”

Primary ciliary dyskinesia: a consensus statement on diagnostic and treatment approaches in children

“…Mutations in this gene have been observed in three families with Kartagener's syndrome, PCD and ODA defects [15]. The involvement of DNAI2 in PCD/Kartagener's syndrome was identified applying a positional and functional candidate-gene approach.…”

“…The majority of the genes identified (table 1) to date for autosomal recessive PCD variants (dynein, axonemal, intermediate chain 1 (DNAI1) and 2 (DNAI2) and heavy chain 5 (DNAH5) and 11 (DNAH11) and thioredoxin domain containing 3 (TXNDC3)) encode outer dynein arm (ODA) components [15][16][17][18][19][20], whereas only one gene (chromosome 14 open reading frame 104 (KTU)) is required for cytoplasmic preassembly of axonemal dyneins [21]. In addition mutations in the two genes, radial spoke head 9 homologue (RSPH9) and 4 homologue A (RSPH4A), have been reported in PCD patients with abnormalities of the central microtubular pair [22].…”

Diagnostic Methods in Primary Ciliary Dyskinesia

“…To date mutations have been identified in 6 genes encoding for proteins that are part of the ODA (DNAH5, DNAI1, DNAI2, DNAL1, NME8 (TXNDC3) and DNAH11) [12,[71][72][73][74][75]. Mutations in DNAH5 and DNAI1 are thought to account for the largest proportion of PCD patients: 30% and 9% respectively [19,[76][77][78][79].…”