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

Victoria Castleman ,Amelia Shoemark,Andrew Bush,Mellisa Dixon,Stephen W Wilson,Claire Hogg,Eddie M.K Chung,Hannah M Mitchison,Robert A Hirst,Colin A Johnson,Keith A Parker,Rahul Chodhari,Orit Reish,Colin Wallis,Leila Romio,Richard D Emes,Saul Purton,Andrew Rutman,René J Herrera ,Nicholas D E Greene ,Patricia Ybot‐González ,Christopher O’callaghan ,Sandra C P De Castro ,R M Gardiner

doi:10.1016/j.ajhg.2009.01.011

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.

Highlights

Primary ciliary dyskinesia (PCD, MIM 242650) refers to a heterogeneous group of genetic ciliopathies characterized by ultrastructural defects in the axonemal structure of ‘‘9þ2’’ motile cilia and sperm flagella.[1]
We have identified mutations in two genes encoding radial spoke head proteins, RSPH9 and RSPH4A, in PCD families that have defects of the central microtubular pair
This is the first report of PCD genes that cause disease associated with cilia-axoneme defects other than a loss or reduction of the outer dynein arms

Summary

Introduction

Primary ciliary dyskinesia (PCD, MIM 242650) refers to a heterogeneous group of genetic ciliopathies characterized by ultrastructural defects in the axonemal structure of ‘‘9þ2’’ motile cilia and sperm flagella.[1] The incidence is estimated at 1:15,000–30,000,2 with higher incidence in certain consanguineous and isolated populations.[3,4] Clinical features reflect the distribution of dysmotile cilia in the body and include neonatal respiratory distress, chronic respiratory infections, sinusitis, and bronchiectasis, due to deficient cilia function in the upper and lower airways. Male and female subfertility occurs as a result of defective sperm flagella and oviduct cilia, respectively. There is occasional hydrocephalus as a result of deficient ependymal cilia.[5,6] In most families, there is apparent randomization of left-right axis development, proposed to result from defective function of embryonic nodal cilia.[7,8] This manifests in about half of patients as situs inversus or more severe laterality defects, such as cardiovascular abnormalities

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