Rare Genetic Kidney Disease and Tethered Cord Collide in a Seven-Year-Old Girl

In the world of rare pediatric disease, some cases arrive like puzzles with two missing pieces instead of one. Physicians at Tianjin Children’s Hospital in China have now reported what they describe as the first genetically confirmed case of nephronophthisis type 1, a hereditary cystic kidney disease, occurring together with a tethered spinal cord in a child. The report, published in BMC Pediatrics, follows a seven-year-old girl whose kidney function collapsed with startling speed, sliding from moderate chronic kidney disease to near end stage renal disease in just five months. The case is a striking reminder that in children with unexplained kidney failure, finding one plausible cause is not the same as finding the true one.

Nephronophthisis is an autosomal recessive disorder, meaning a child must inherit a defective copy of the responsible gene from both parents to develop the disease. It is caused by mutations in genes that encode components of the primary cilium, a tiny antenna-like structure projecting from nearly every cell in the body, making nephronophthisis part of a broader family of conditions known as ciliopathies. Within the kidney, defective ciliary signaling disrupts the architecture of the renal tubules, leading to chronic tubulointerstitial inflammation, fibrosis, and the eventual formation of cysts at the corticomedullary junction. Despite its name, which references the cysts, nephronophthisis is not primarily a cystic disease in the way polycystic kidney disease is; its hallmark is progressive scarring that silently destroys filtering capacity. It is a leading genetic cause of end stage renal disease in children and adolescents worldwide.

The clinical signature of nephronophthisis is notoriously subtle in its early stages. Classic textbook features include polydipsia, excessive thirst, and polyuria, the production of abnormally large volumes of dilute urine, both stemming from the kidney’s impaired ability to concentrate urine. Anemia, growth retardation, and fatigue often follow as renal function declines. What makes the disease so dangerous is precisely how quietly it progresses: many children reach advanced chronic kidney disease before anyone notices, because the surviving nephrons compensate for the damaged ones for years. Type 1 nephronophthisis, caused by defects in the NPHP1 gene, is the most common form and typically follows a juvenile course, with most patients reaching kidney failure within the first two decades of life.

The girl in this report arrived at medical attention almost by accident. She was admitted after a visit for abdominal pain, during which laboratory testing revealed renal dysfunction that no one had suspected. Her serum creatinine, a waste molecule that accumulates when the kidneys fail to filter blood adequately, measured 101.7 micromoles per liter, and her estimated glomerular filtration rate, the standard measure of kidney filtering capacity, stood at 45.2 milliliters per minute per 1.73 square meters of body surface area. Those numbers placed her in stage 3 chronic kidney disease, a level at which many adults already feel unwell. Yet this child had none of the classic thirst and urination symptoms that usually announce nephronophthisis. The only urinary clue was a relatively low urine specific gravity, a laboratory measure indicating that her kidneys could not concentrate urine properly, a finding easily overlooked in a child with other complaints.

Her history held another thread: a long-standing pattern of enuresis, or bedwetting, and daytime urinary incontinence. That symptom pointed the clinical team toward a completely different diagnostic territory, one involving the nervous system rather than inherited kidney disease. Magnetic resonance imaging of her spine revealed separation of the cauda equina, the bundle of nerve roots at the base of the spinal cord, from the filum terminale, the fibrous strand that anchors the cord to the tailbone. This finding is characteristic of a tethered cord, a condition in which the spinal cord is abnormally anchored and stretched as a child grows. Tethered cord is one of the important causes of neurogenic bladder in children, a dysfunction in which the bladder fails to store or empty urine properly because its nerve supply is compromised.

Here the diagnostic picture grew genuinely tangled. A neurogenic bladder can, over time, drive secondary chronic kidney disease by generating high pressures, incomplete emptying, and recurrent infections that scar the kidneys. Abdominal computed tomography in this patient showed mild bladder wall thickening, measured at 4 millimeters under adequate bladder distension, a finding consistent with chronic bladder strain. Yet a voiding cystourethrogram, an X-ray study in which contrast dye is instilled into the bladder while the child urinates, detected no vesicoureteral reflux, the backward flow of urine toward the kidneys, and no structural abnormalities. In other words, the anatomical evidence that the tethered cord was actively damaging her kidneys was thin. The team faced a genuine diagnostic fork: was this a primary genetic kidney disease, a secondary kidney injury from bladder dysfunction, or both?

The answer came from genetic testing, which identified a homozygous pathogenic deletion of exons 1 through 20 of the NPHP1 gene. That is a devastating molecular finding: essentially the entire functional span of the gene was missing from both of her chromosomes, leaving her cells unable to produce the normal ciliary protein. Large homozygous deletions of this kind are the most common disease-causing mechanism in NPHP1-related nephronophthisis. The result settled the central question. This child carried a primary, inherited, progressive kidney disease, and the tethered cord, while real and requiring treatment, was at minimum not the sole explanation for her failing kidneys. The co-occurrence of the two conditions had, to the authors’ knowledge, never been reported before.

Management proceeded on both fronts. The girl underwent neurosurgical intervention to release the tethered cord, the standard treatment aimed at preventing further neurological and bladder deterioration. But her kidneys did not stabilize. Over the following five months, her renal function progressed rapidly from stage 3 chronic kidney disease to pre-end stage renal disease, the threshold at which dialysis or transplantation becomes necessary. The authors of the report suggest that this trajectory underscores a critical clinical lesson: the presence of an identifiable secondary injury factor, such as a neurogenic bladder, can create a seductive diagnostic shortcut, leading clinicians to attribute all renal decline to that factor while an underlying genetic disease continues its silent advance. In this case, the tethered cord was found and treated, yet the primary disease ran its course regardless.

The broader message of the report reaches well beyond this single patient. Nephronophthisis is genetically heterogeneous, with more than twenty implicated genes, and its phenotype can be modified by additional syndromic features ranging from retinal degeneration to liver fibrosis. Distinguishing a primary ciliopathy from secondary kidney injury requires a level of suspicion that, the authors argue, should translate into early genetic testing for children with unexplained chronic kidney disease, even when a plausible alternative cause has already been identified. Modern sequencing has made such testing faster and more accessible than ever, and a molecular diagnosis carries consequences that imaging alone cannot deliver: it clarifies prognosis, informs the risk to future siblings, shapes decisions about transplant timing, and can reveal extrarenal manifestations that demand surveillance. For a seven-year-old whose kidneys failed in months, the genetic answer arrived, but the case stands as a warning written in real time. When a child’s kidneys fail without explanation, one diagnosis should never be allowed to end the search.

Subject of Research: A pediatric case report of genetically confirmed nephronophthisis type 1 co-occurring with tethered cord and rapid progression to end stage renal disease

Article Title: A case report of nephronophthisis type 1 (NPHP1) complicated with tethered cord in a pediatric patient: clinical phenotype and rapid progression to end stage renal disease

Article References: Deng, H., Fan, S., Jiang, Y., Yang, L., & Wang, W. (2026). A case report of nephronophthisis type 1 (NPHP1) complicated with tethered cord in a pediatric patient: clinical phenotype and rapid progression to end stage renal disease. BMC Pediatrics. https://doi.org/10.1186/s12887-026-07771-w

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07771-w

Keywords: nephronophthisis, NPHP1, tethered cord, chronic kidney disease, end stage renal disease, pediatric nephrology, genetic testing, ciliopathy, neurogenic bladder, case report, autosomal recessive, renal dysfunction