Mutations in Radial Spoke Head Protein Genes RSPH9 and RSPH4A Cause Primary Ciliary Dyskinesia with Central-Microtubular-Pair Abnormalities

Abstract

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous inherited disorder arising from dysmotility of motile cilia and sperm. This is associated with a variety of ultrastructural defects of the cilia and sperm axoneme that affect movement, leading to clinical consequences on respiratory-tract mucociliary clearance and lung function, fertility, and left-right body-axis determination. We performed whole-genome SNP-based linkage analysis in seven consanguineous families with PCD and central-microtubular-pair abnormalities. This identified two loci, in two families with intermittent absence of the central-pair structure (chromosome 6p21.1, Zmax 6.7) and in five families with complete absence of the central pair (chromosome 6q22.1, Zmax 7.0). Mutations were subsequently identified in two positional candidate genes, RSPH9 on chromosome 6p21.1 and RSPH4A on chromosome 6q22.1. Haplotype analysis identified a common ancestral founder effect RSPH4A mutation present in UK-Pakistani pedigrees. Both RSPH9 and RSPH4A encode protein components of the axonemal radial spoke head. In situ hybridization of murine Rsph9 shows gene expression restricted to regions containing motile cilia. Investigation of the effect of knockdown or mutations of RSPH9 orthologs in zebrafish and Chlamydomonas indicate that radial spoke head proteins are important in maintaining normal movement in motile, "9+2"-structure cilia and flagella. This effect is rescued by reintroduction of gene expression for restoration of a normal beat pattern in zebrafish. Disturbance in function of these genes was not associated with defects in left-right axis determination in humans or zebrafish.

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

“…Mutations within radial spoke head genes have been identified in a few families affected with PCD with associated central pair abnormalities [22]. Patients had no situs inversus.…”

“…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]. In a minority of cases, other inheritance patterns have been recognised [23].…”

Diagnostic Methods in Primary Ciliary Dyskinesia

“…However, numbers of patients with individual genetic defects were extremely low in the only study [48], and larger multi-centre studies are called for to investigate genotype-ciliary phenotype relationships. Subtle functional defects are increasingly recognised to cause phenotypic disease [49,50] and analyses by scientists with substantial experience of normal and abnormal ciliary beating is essential. In expert hands, using HVMA to assess CBP, dyskinesia on >90% ciliated edges has 97% sensitivity and 95% specificity to predict a TEM diagnosis of PCD [45].…”

“…It is also informative to examine the longitudinal sections as rare defects e.g. RSPH4A, can be identified by distinctive patterning [50].…”

“…Male patients with mutations in CCDC114 (coding for a docking protein for the ODA) are generally fertile [70]. Situs abnormalities are not observed in patients with mutations affecting the central pair [64] or radial spokes [49,50,69], nor in patients with reduced generation of multiple motile cilia [13,14]. However, it is likely that variable clinical pictures occur between patients with different mutations within a particular gene and even between patients with identical mutations.…”