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NPHP4
nephrocystin 4
NPHP4 is located on the short (p) arm of chromosome 1, at band 1p36.31. Arm ratio per GRCh38 - banding schematic.
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Overview
NPHP4 encodes a member of the nephrocystin protein family, which are structural and regulatory components of primary cilia. These cellular projections act as sensory organelles, detecting chemical and mechanical signals from the extracellular environment and coordinating developmental pathways during embryogenesis and tissue maintenance.
Pathogenic variants in NPHP4 are inherited in an autosomal recessive pattern, meaning that affected individuals carry two altered copies of the gene - one from each parent. Carriers with a single variant typically show no symptoms. NPHP4-related disease primarily affects the kidneys, where ciliary dysfunction leads to progressive tubulointerstitial damage and eventual renal failure.
What the gene does
Nephrocystin 4 localises to the transition zone of primary cilia and to centrosomes, cellular structures that organise microtubules and coordinate cell division. The protein participates in ciliary assembly, maintenance of the ciliary diffusion barrier, and regulation of signalling pathways that control kidney tubule development and homeostasis.
Within the cilium, nephrocystin 4 interacts with other nephrocystin family members and ciliary transport machinery to ensure proper cargo delivery to and from the ciliary compartment. This coordinated trafficking is essential for maintaining the distinct protein composition of cilia compared with the rest of the cell. Disruption of nephrocystin 4 function impairs ciliary signalling cascades, including pathways involved in planar cell polarity and oriented cell division, which are critical for the three-dimensional architecture of kidney tubules. Loss of these regulatory mechanisms contributes to cyst formation and progressive kidney fibrosis.
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Chromosome location
NPHP4 is located on chromosome 1 at position p36.31, near the end of the short arm. The gene spans approximately 80 kilobases of genomic DNA and contains 29 coding exons that are transcribed and spliced to produce the mature messenger RNA template for nephrocystin 4 synthesis.
Protein structure
Nephrocystin 4 is a 1426-amino-acid protein with a complex domain organisation. The carboxy-terminal region, spanning amino acids 823-1426, is sufficient for localisation to basal bodies - the structures that anchor cilia to the cell surface. Two notable disordered regions occur at amino acids 450-536 and 896-935; these intrinsically disordered segments may provide structural flexibility and enable protein-protein interactions with multiple binding partners within the ciliary proteome.
Key variants
Pathogenic variants in NPHP4 include nonsense changes that introduce premature stop codons, frameshift deletions or insertions that disrupt the reading frame, and splice-site alterations that result in aberrant messenger RNA processing. These loss-of-function variants typically abolish or severely reduce nephrocystin 4 protein levels, compromising ciliary structure and signalling in affected tissues.
Sample of pathogenic variants
10 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 |
|---|---|---|---|---|
c.111G>A | p.Trp37Ter | Pathogenic/Likely pathogenic | ★★☆☆ | NPHP4-related disorder |
c.1692_1704del | p.Ala565fs | Pathogenic/Likely pathogenic | ★★☆☆ | Nephronophthisis |
c.175C>T | p.Arg59Ter | Pathogenic | ★★☆☆ | Nephronophthisis |
c.1843C>T | p.Gln615Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Nephronophthisis 4 |
c.2007del | p.Phe670fs | Pathogenic/Likely pathogenic | ★★☆☆ | Nephronophthisis 4 |
c.2611C>T | p.Arg871Ter | Pathogenic/Likely pathogenic | ★★☆☆ | NPHP4-related disorder |
c.2932del | p.Glu978fs | Pathogenic | ★★☆☆ | NPHP4-related disorder |
c.3148del | p.Gln1050fs | Pathogenic/Likely pathogenic | ★★☆☆ | Nephronophthisis |
c.3272dup | p.Ser1092fs | Pathogenic | ★★☆☆ | Cystic renal disease |
c.3418G>T | p.Glu1140Ter | Pathogenic/Likely pathogenic | ★★☆☆ | NPHP4-related disorder |
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 NPHP4 cause nephronophthisis, a progressive kidney disorder characterised by tubulointerstitial fibrosis, cyst formation at the corticomedullary junction, and gradual loss of renal function. Nephronophthisis is among the most common genetic causes of kidney failure in children and young adults. Clinical features generally include polyuria, polydipsia, and anaemia, with most affected individuals progressing to end-stage renal disease requiring dialysis or transplantation during the first two decades of life.
Inheritance pattern
Conditions caused by pathogenic NPHP4 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
NPHP4 holds green classification status on nine NHS Genomic Medicine Service gene panels, reflecting robust evidence supporting its role in inherited kidney and ciliopathy disorders. Relevant panels include Cystic kidney disease, Renal ciliopathies, Tubulointerstitial kidney disease, Unexplained kidney failure in young people, Rare multisystem ciliopathy disorders, Ophthalmological ciliopathies, Retinal disorders, Fetal anomalies, and the Developmental Disorders Genotype to Phenotype database. These classifications indicate that NPHP4 testing may be offered through NHS genomic testing pathways for individuals presenting with clinical features consistent with ciliopathies or unexplained progressive kidney disease.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What inheritance pattern does NPHP4 follow?
NPHP4-related conditions are inherited in an autosomal recessive pattern. An affected individual inherits one altered copy from each parent, while parents who are carriers typically show no symptoms.
At what age does nephronophthisis typically present?
Nephronophthisis caused by NPHP4 variants generally manifests during childhood or adolescence, with most affected individuals progressing to kidney failure within the first two decades of life.
Can NPHP4 variants affect organs other than the kidneys?
While kidney disease is the primary feature, some individuals with NPHP4-related nephronophthisis may develop retinal degeneration or other ciliopathy-related manifestations, though renal involvement predominates in most cases.