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NPHP3
nephrocystin 3
NPHP3 is located on the long (q) arm of chromosome 3, at band 3q22.1. Arm ratio per GRCh38 - banding schematic.
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Overview
NPHP3 (nephrocystin 3) is located on chromosome 3 at position 3q22.1 and encodes a 1,330 amino acid protein that functions within primary cilia. Primary cilia are antenna-like projections that sense environmental signals and coordinate cellular responses during development and tissue maintenance. Nephrocystin-3 contributes to the structural integrity of cilia and participates in signalling pathways essential for normal organ development, particularly in the kidneys, retina, and central nervous system.
Pathogenic variants in NPHP3 follow an autosomal recessive inheritance pattern, meaning two altered copies (one from each parent) are required to cause disease. The gene is included in multiple NHS Genomic Medicine Service gene panels for ciliopathies and kidney disorders, reflecting its clinical importance in the UK diagnostic pathway. Carrier screening can identify individuals who carry one pathogenic variant and may be at risk of having affected children if their partner is also a carrier.
What the gene does
Nephrocystin-3 is a ciliary protein that localises to the transition zone and inversin compartment of primary cilia, regions critical for controlling what enters and exits the ciliary structure. The protein functions as a scaffolding molecule, bringing together other proteins required for ciliary assembly and maintenance. Through its protein-protein interactions, nephrocystin-3 helps coordinate signalling cascades involved in planar cell polarity, Wnt signalling, and Hedgehog pathways - all essential for proper tissue patterning during embryonic development.
The protein appears particularly important in epithelial tissues where coordinated ciliary function is required. In the kidney, nephrocystin-3 contributes to the normal architecture of renal tubules. In the retina, it supports photoreceptor cell structure and function. The protein also participates in centrosome function during cell division, linking ciliary biology to cell cycle control. Disruption of nephrocystin-3 function leads to defective cilia that cannot properly sense or transmit signals, resulting in the progressive tissue damage characteristic of ciliopathies.
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Chromosome location
NPHP3 is located on the long arm of chromosome 3 at cytogenetic band 3q22.1. This chromosomal region contains multiple genes involved in developmental processes. The NPHP3 gene spans a substantial genomic interval and contains multiple exons that are transcribed and spliced together to produce the mature messenger RNA template for nephrocystin-3 protein synthesis.
Protein structure
Nephrocystin-3 is organised into several distinct structural regions that mediate its scaffolding functions. The protein contains a coiled coil domain spanning amino acids 83-207 near the N-terminus, which typically facilitates protein-protein interactions. The most prominent feature is an extensive array of tetratricopeptide repeat (TPR) motifs in the C-terminal half of the protein. These include TPR 1 through TPR 11, distributed from amino acid 471 through to position 1294.
TPR domains are structural motifs that form scaffolds for assembling multiprotein complexes, consistent with nephrocystin-3's role in organising ciliary protein networks. The protein terminates in a disordered region from amino acids 1296-1330, which may provide flexibility for dynamic protein interactions. This domain architecture allows nephrocystin-3 to serve as a molecular platform, coordinating the assembly and positioning of other nephrocystin family members and ciliary transport machinery.
Key variants
Pathogenic variants in NPHP3 include missense changes, nonsense mutations, and small insertions or deletions that disrupt protein function. Loss-of-function variants that eliminate nephrocystin-3 expression or severely impair its structural integrity are commonly associated with more severe presentations. The distribution of variants across the gene reflects the functional importance of different domains, with variants affecting the TPR repeat regions often disrupting critical protein-protein interactions required for ciliary function.
Sample of pathogenic variants
3 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
g.(?_132410016)_(132411682_?)del | - | Pathogenic | ★☆☆☆ | Nephronophthisis |
g.(?_132418742)_(132424678_?)del | - | Pathogenic | ★☆☆☆ | Nephronophthisis |
g.(?_132681890)_(132684814_?)del | - | Pathogenic | ★☆☆☆ | Nephronophthisis |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Biallelic pathogenic variants in NPHP3 cause nephronophthisis, a ciliopathy characterised by progressive kidney disease. The condition typically presents in childhood or adolescence with gradual decline in kidney function, often progressing to end-stage renal disease. Some individuals with NPHP3-related nephronophthisis also develop retinal degeneration, liver abnormalities, or skeletal features, reflecting the widespread importance of ciliary function across multiple organ systems. The severity and range of features can vary considerably between affected individuals, even those with the same genetic variants.
Inheritance pattern
Conditions caused by pathogenic NPHP3 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
NPHP3 has been assigned green (high evidence) status on multiple NHS Genomic Medicine Service gene panels, indicating strong confidence in its disease association. The gene appears on panels for CAKUT (congenital anomalies of the kidney and urinary tract), cystic kidney disease, neurological ciliopathies, ophthalmological ciliopathies, rare multisystem ciliopathy disorders, renal ciliopathies, retinal disorders, tubulointerstitial kidney disease, and unexplained kidney failure in young people. This broad panel membership reflects the variable presentation of NPHP3-related disorders and ensures the gene is analysed when ciliopathy is suspected across different clinical contexts. Green classification on these panels means NPHP3 variants are reported and acted upon within NHS diagnostic laboratories when identified in appropriate clinical scenarios.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What does it mean to be a carrier of an NPHP3 variant?
A carrier has one pathogenic NPHP3 variant and one normal copy. Carriers typically have no symptoms because the normal copy provides sufficient nephrocystin-3 function. However, if both parents are carriers, each pregnancy has a 25% chance of inheriting two pathogenic variants and developing nephronophthisis.
How is NPHP3-related nephronophthisis diagnosed?
Diagnosis involves clinical assessment of kidney function, imaging studies to detect characteristic renal changes, and genetic testing to identify biallelic NPHP3 variants. Additional investigations may assess eyes, liver, and other organs that can be affected in ciliopathies.
Are all NPHP3 variants equally severe?
No, the clinical impact varies depending on how severely the variant disrupts nephrocystin-3 function. Complete loss-of-function variants may cause earlier onset or more extensive organ involvement, whilst variants that partially preserve protein activity may result in milder presentations, though individual outcomes remain difficult to predict.