A Male Patient with a Solitary Kidney and Severe Proteinuria Diagnosed with Dent Disease 1

A solitary kidney rarely causes renal dysfunction or hypertension during childhood. However, the presence of proteinuria raises concern for progressive renal impairment, warranting detailed evaluation for possible compensatory hyperfiltration or coexisting glomerular disease. Dent disease is a rare X-linked proximal tubulopathy characterized by low-molecular-weight proteinuria (LMWP) due to defective receptor-mediated endocytosis in the proximal tubules. Although uncommon, it represents an important differential diagnosis in children with persistent proteinuria. We report a male patient with a solitary kidney secondary to multicystic dysplastic kidney (MCDK) who developed marked proteinuria and was ultimately diagnosed with Dent disease 1 by genetic analysis.

A 14-year-old boy had been prenatally diagnosed with multiple cysts in the right kidney on fetal ultrasonography, and postnatal imaging confirmed right-sided MCDK. He had no extrarenal malformations, and his growth and development were normal. At 11 months of age, urinalysis showed 1+ hematuria and 1+ proteinuria. At 2 years of age, following a streptococcal infection, urinalysis revealed 1+ hematuria and 3+ proteinuria. Microscopy demonstrated approximately 30 red blood cells per high-power field and a urinary protein-to-creatinine ratio (UPCR) of 3.2 g/gCr. Although acute post-streptococcal glomerulonephritis was suspected, there was no hypertension or hypocomplementemia. Because persistent proteinuria (UPCR 1–3 g/gCr) continued, a renal biopsy was performed six months later. Histopathological examination revealed minimal glomerular change without glomerular enlargement, tubular atrophy, or interstitial inflammation. Immunofluorescence showed no deposition of C3 or immunoglobulins. Despite treatment with renin–angiotensin system inhibitors, the UPCR remained between 1 and 3 g/gCr. The urinary β2-microglobulin level was markedly elevated at 153 μg/mgCr, indicating proximal tubular dysfunction.

Differential diagnoses for tubular dysfunction, including mitochondrial disorders, were excluded. At age 14, next-generation sequencing with a renal disease gene panel identified a pathogenic variant in the CLCN5 gene, confirming Dent disease 1.

In patients with a solitary kidney presenting with proteinuria, differential diagnoses usually include compensatory hyperfiltration or secondary glomerular disease. In our patient, the absence of such findings emphasized the importance of genetic analysis in establishing the diagnosis of Dent disease. Although Dent disease primarily causes LMWP, it often presents with total proteinuria and microscopic hematuria, mimicking glomerular disease. To our knowledge, this is the first reported case of coexisting Dent disease and MCDK, suggesting that these two conditions can occur independently rather than being pathogenetically related. Genetic testing was crucial for confirming the diagnosis and preventing unnecessary or ineffective treatments. This case highlights that, when persistent proteinuria is observed in a child with a solitary kidney, clinicians should consider not only glomerular diseases but also hereditary tubular disorders such as Dent disease. Early recognition and appropriate genetic evaluation are essential for accurate diagnosis, prognosis, family counseling, and long-term management.