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PubMed This is a summary of 14 peer-reviewed journal articles Updated
Nephrology

Diagnosis & Testing: Confirming NPHP

At a Glance

Nephronophthisis (NPHP) is definitively diagnosed using advanced genetic testing, which has largely replaced invasive kidney biopsies. Early ultrasounds may appear normal, but genetic tests confirm the exact mutation and guide future care.

The process of diagnosing Nephronophthisis (NPHP) has evolved significantly in recent years. Because the symptoms are often vague, doctors rely on a combination of medical imaging and advanced genetic technology to confirm the diagnosis and determine the best path forward.

What Imaging Reveals (and What it Might Miss)

A kidney ultrasound is often the first step when a doctor suspects a kidney issue. However, NPHP is unique because the kidneys can look surprisingly “normal” in the early stages of the disease [1][2].

The “Pre-Cystic” Phase

In many kidney diseases, large cysts are the primary sign. In NPHP, however, there is a pre-cystic phase [1]. During this time, the kidneys may be normal in size and show no cysts at all [2]. This can sometimes lead to a delay in diagnosis if a doctor is only looking for large cysts. Cysts typically begin to appear much later in the disease process, as chronic scarring becomes more advanced.

Characteristic Ultrasound Signs

As the disease progresses, certain patterns typically emerge on the ultrasound:

  • Increased Echogenicity: The kidney tissue appears “brighter” or “whiter” than usual on the screen, which indicates scarring (fibrosis) [1][3].
  • Loss of Corticomedullary Differentiation: In a healthy kidney, there is a clear visible boundary between the outer layer (cortex) and the inner layer (medulla). In NPHP, this boundary often disappears [1][4].
  • Small-to-Normal Size: Unlike other cystic diseases where kidneys become very large, NPHP kidneys usually stay normal in size or even shrink as scarring increases [1].
  • Small Cysts: If cysts do appear later, they are usually very small and located at the junction between the inner and outer layers of the kidney [1][2].

The Gold Standard: Genetic Testing

Today, Next-Generation Sequencing (NGS) and Whole Exome Sequencing (WES) are the standard methods for diagnosing NPHP [4][5]. These tests act like a powerful “spell-checker” for your child’s DNA, looking for mutations in the genes known to cause the disease [6][7].

Genetic testing is preferred because:

  1. It is Definitive: It can confirm NPHP even when ultrasound results are unclear or normal [8].
  2. It Identifies the Subtype: Knowing the specific gene (such as NPHP1) helps doctors predict how quickly the disease might progress and which other organs need to be monitored [9][10].
  3. It Informs the Family: It clarifies the risk for siblings and helps in planning for future pregnancies [11].

Moving Away from Kidney Biopsy

In the past, a kidney biopsy—where a small needle is used to take a piece of kidney tissue—was the only way to see the characteristic scarring and “tubulointerstitial nephritis” of NPHP [12][13].

While a biopsy can still provide valuable information, it is an invasive procedure that carries risks like bleeding. Because genetic testing is so accurate and can provide a definitive diagnosis from a simple blood draw, it has largely replaced the need for a biopsy in many cases [4][10]. Your doctor may still recommend a biopsy if the genetic tests are inconclusive, but for many families, the genetic “blueprint” provides all the answers needed [14].

Common questions in this guide

Why didn't my child's first kidney ultrasound show any cysts?
In Nephronophthisis, there is often an early pre-cystic phase where the kidneys look normal in size and show no cysts. Cysts typically develop much later in the disease process as kidney scarring becomes more advanced.
Is a kidney biopsy required to diagnose NPHP?
A kidney biopsy is no longer the standard requirement for diagnosing NPHP. Because modern genetic testing is highly accurate and requires only a blood draw, it has largely replaced invasive biopsies in most cases.
What does increased echogenicity mean on a kidney ultrasound?
Increased echogenicity means the kidney tissue appears brighter or whiter than usual on the ultrasound screen. This brightness typically indicates scarring or fibrosis within the kidney tissue, which is a common sign of Nephronophthisis.
Why is genetic testing considered the gold standard for diagnosing NPHP?
Genetic testing definitively confirms the disease even when ultrasound results are unclear. It also identifies the specific gene mutation involved, helping doctors predict disease progression, monitor other at-risk organs, and clarify risks for siblings.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Was a 'Copy Number Variation' (CNV) analysis included in my child's genetic testing to specifically look for the NPHP1 deletion?
  2. 2.Does the ultrasound show 'increased echogenicity' or a 'loss of corticomedullary differentiation'?
  3. 3.Since genetic testing is now the standard, is a kidney biopsy still necessary for my child?
  4. 4.Why were cysts not visible on the first ultrasound, and should we repeat the imaging later?
  5. 5.If we find a specific genetic mutation, what does that tell us about the risk of the disease affecting other organs like the eyes or liver?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (14)
  1. 1

    Clinical and genetic analyses of a Dutch cohort of 40 patients with a nephronophthisis-related ciliopathy.

    Stokman MF, van der Zwaag B, van de Kar NCAJ, et al.

    Pediatric nephrology (Berlin, Germany) 2018; (33(10)):1701-1712 doi:10.1007/s00467-018-3958-7.

    PMID: 29974258
  2. 2

    Rapidly Progressive Kidney Failure With Transient Non-Cystic Kidney Enlargement: A Case Report Highlighting Delayed Medullary Cyst Formation.

    Ito H, Mashiko S, Mizuno S, et al.

    Nephrology (Carlton, Vic.) 2026; (31(4)):e70198 doi:10.1111/nep.70198.

    PMID: 41878779
  3. 3

    Hippo signaling-a central player in cystic kidney disease?

    Müller RU, Schermer B

    Pediatric nephrology (Berlin, Germany) 2020; (35(7)):1143-1152 doi:10.1007/s00467-019-04299-3.

    PMID: 31297585
  4. 4

    Case Report: A Novel In-Frame Deletion of GLIS2 Leading to Nephronophthisis and Early Onset Kidney Failure.

    Al Alawi I, Powell L, Rice SJ, et al.

    Frontiers in genetics 2021; (12()):791495 doi:10.3389/fgene.2021.791495.

    PMID: 34917135
  5. 5

    Whole exome sequencing identifies causative mutations in the majority of consanguineous or familial cases with childhood-onset increased renal echogenicity.

    Braun DA, Schueler M, Halbritter J, et al.

    Kidney international 2016; (89(2)):468-475 doi:10.1038/ki.2015.317.

    PMID: 26489029
  6. 6

    Challenges in Clinicogenetic Correlations: One Phenotype - Many Genes.

    Gannamani R, van der Veen S, van Egmond M, et al.

    Movement disorders clinical practice 2021; (8(3)):311-321 doi:10.1002/mdc3.13163.

    PMID: 33816658
  7. 7

    High diagnostic yield of targeted next-generation sequencing panel as a first-tier molecular test for the patients with myopathy or muscular dystrophy.

    Çavdarlı B, Köken ÖY, Satılmış SBA, et al.

    Annals of human genetics 2023; (87(3)):104-114 doi:10.1111/ahg.12492.

    PMID: 36575883
  8. 8

    Spectrum of Mutations in Pediatric Non-glomerular Chronic Kidney Disease Stages 2-5.

    Wang X, Xiao H, Yao Y, et al.

    Frontiers in genetics 2021; (12()):697085 doi:10.3389/fgene.2021.697085.

    PMID: 34295353
  9. 9

    Defective INPP5E distribution in NPHP1-related Senior-Loken syndrome.

    Ning K, Song E, Sendayen BE, et al.

    Molecular genetics & genomic medicine 2021; (9(1)):e1566 doi:10.1002/mgg3.1566.

    PMID: 33306870
  10. 10

    [Clinical phenotype characteristics and genetic analysis in children with nephronophthisis and related syndromes caused by different gene mutations].

    Zhao X, Jiang LJ, Rong ZH, et al.

    Zhongguo dang dai er ke za zhi = Chinese journal of contemporary pediatrics 2023; (25(8)):831-836 doi:10.7499/j.issn.1008-8830.2303020.

    PMID: 37668031
  11. 11

    Whole Exome Sequencing Reveals a XPNPEP3 Novel Mutation Causing Nephronophthisis in a Pediatric Patient

    Alizadeh R, Jamshidi S, Keramatipour M, et al.

    Iranian biomedical journal 2020; (24(6)):405-8 doi:10.29252/ibj.24.6.400.

    PMID: 32660933
  12. 12

    [Unexpected diagnosis of nephronopthisis in the genetic study of hypertension due to histological diagnosis of benign nephroangioesclerosis evolved in a young caucasian patient].

    Heras Benito M, Pérez García ML, Antúnez Plaza P, Montero Mateos E

    Hipertension y riesgo vascular 2023; (40(3)):150-153 doi:10.1016/j.hipert.2023.02.001.

    PMID: 36894476
  13. 13

    Novel pathogenic MAPKBP1 variant in a family with nephronophthisis.

    Al-Hamed MH, Alzaidan H, Hussein M, et al.

    Clinical kidney journal 2021; (14(2)):728-730 doi:10.1093/ckj/sfaa090.

    PMID: 33623699
  14. 14

    Fluorescence in situ hybridization for the diagnosis of NPHP1 deletion-related nephronophthisis on renal biopsy.

    Larsen CP, Bonsib SM, Beggs ML, Wilson JD

    Human pathology 2018; (81()):71-77 doi:10.1016/j.humpath.2018.06.021.

    PMID: 29949740

This page explains Nephronophthisis (NPHP) diagnostic methods for educational purposes. Always consult a pediatric nephrologist or genetic counselor regarding testing and diagnosis for your child's specific condition.

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