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RSPH9
radial spoke head component 9
RSPH9 is located on the short (p) arm of chromosome 6, at band 6p21.1. Arm ratio per GRCh38 - banding schematic.
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Overview
RSPH9 encodes a protein component of the radial spoke head, a structural complex found within motile cilia and flagella. Cilia are microscopic hair-like projections that extend from many cell types throughout the body, including cells lining the respiratory tract, reproductive organs, and brain ventricles. The radial spokes connect the central pair of microtubules to the outer doublet microtubules within the ciliary axoneme, coordinating the bending motion that enables effective ciliary beating.
When RSPH9 function is compromised through pathogenic variants, the radial spoke structure becomes unstable or incomplete, preventing normal ciliary movement. This leads to impaired mucociliary clearance in the airways, resulting in chronic respiratory symptoms. RSPH9-related conditions follow an autosomal recessive inheritance pattern, meaning pathogenic variants must be present on both gene copies for disease to manifest.
What the gene does
The RSPH9 protein is localised to the radial spoke head within the ciliary axoneme, where it contributes to the structural integrity of this complex. Radial spokes are T-shaped protein assemblies that project from each of the nine outer microtubule doublets towards the central pair apparatus at regular intervals along the cilium length. These structures transmit regulatory signals that control the dynein motor proteins responsible for generating the sliding forces between microtubules that produce ciliary bending.
RSPH9 works in concert with other radial spoke head proteins to maintain the spoke's structural stability and ensure proper communication between the central apparatus and the outer dynein arms. This coordination is essential for converting the sliding motion of microtubules into the asymmetric, wave-like beating pattern required for effective mucus transport in the airways. Without functional RSPH9, the radial spoke head may be absent or structurally abnormal, leading to static or dyskinetic ciliary movement that fails to clear respiratory secretions efficiently.
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Chromosome location
RSPH9 is located on the short arm of chromosome 6 at position 21.1 (6p21.1). This chromosomal region contains multiple genes involved in diverse cellular functions. The genomic structure of RSPH9 and the number of exons encoding the protein have not been comprehensively detailed in standard reference databases.
Protein structure
Domain architecture has not been experimentally characterised in detail for this protein. The RSPH9 protein consists of 276 amino acids and is predicted to contain regions that facilitate its incorporation into the radial spoke head complex and interaction with neighbouring spoke components. Structural studies of radial spoke assemblies suggest RSPH9 likely participates in protein-protein interactions necessary for spoke head assembly and attachment to the central microtubule pair.
Key variants
Pathogenic variants in RSPH9 associated with primary ciliary dyskinesia are typically loss-of-function changes that abolish or severely reduce protein production or function. These include nonsense variants that introduce premature stop codons, frameshift variants resulting from small insertions or deletions, and splice-site variants that disrupt normal mRNA processing. Missense variants affecting critical amino acids required for protein folding or radial spoke assembly have also been reported in affected individuals.
No pathogenic or likely-pathogenic ClinVar variants recorded yet for this gene.
Associated conditions
Pathogenic variants in RSPH9 cause primary ciliary dyskinesia, a genetically heterogeneous disorder characterised by chronic respiratory tract infections, bronchiectasis, and sino-pulmonary disease. Individuals with RSPH9-related ciliary dysfunction typically present with neonatal respiratory distress, persistent wet cough, and recurrent chest infections from early childhood. Unlike some forms of primary ciliary dyskinesia caused by defects in other genes, RSPH9 variants are generally not associated with laterality defects such as situs inversus, as radial spoke defects tend to preserve the ciliary structures required for embryonic left-right patterning while still impairing respiratory ciliary clearance.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic RSPH9 variants typically follow autosomal recessive inheritance.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
UK clinical status
RSPH9 appears on multiple NHS Genomic Medicine Service gene panels relevant to respiratory and developmental disorders. It holds green classification status on the Fetal anomalies panel (version R21), the Primary ciliary disorders panel, and the Respiratory ciliopathies including non-CF bronchiectasis panel (version R189). Green classification indicates strong evidence supporting the gene-disease relationship, meaning RSPH9 variants may be reported in diagnostic genomic testing for individuals with relevant clinical presentations within the NHS.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What symptoms might suggest an RSPH9-related condition?
Individuals with RSPH9-related primary ciliary dyskinesia typically experience chronic wet cough, recurrent respiratory infections from infancy, persistent nasal congestion, and ear infections. Neonatal respiratory distress and later development of bronchiectasis are common features.
How is RSPH9-related primary ciliary dyskinesia inherited?
RSPH9-related conditions follow an autosomal recessive inheritance pattern. An individual must inherit a pathogenic variant from both parents to develop the condition. Carriers with a single pathogenic variant typically show no symptoms.
Do RSPH9 variants cause organ laterality defects?
RSPH9 variants are generally not associated with situs inversus or other laterality abnormalities, unlike some other forms of primary ciliary dyskinesia. The radial spoke defects caused by RSPH9 variants typically impair respiratory ciliary function while preserving embryonic laterality determination.