Renal histology and MRI in a 25-year-old Japanese man with nephronophthisis 4 .

We investigated a 25-year-old Japanese man who had polycystic kidneys and end-stage renal failure without a positive family history. Ultrasonography revealed enlarged kidneys with increased echogenicity and multiple cystic lesions. MRI showed replacement of both kidneys by cystic lesions without definite walls. Renal biopsy demonstrated interstitial fibrosis, especially at the corticomedullary junction. The residual tubular system showed starfish-like disruption. Tubules with cystic dilation were mainly the distal loop of Henle and the distal tubules since immunohistochemical staining was positive for cytokeratin 7 (the distal loop of Henle and the distal tubule) and Tamm-Horsfall protein (the distal loop of Henle), while being negative for aquaporin 3 (the collecting duct) and CD10 (proximal tubule). Comprehensive genetic analysis identified compound heterozygous missense mutations of <italic>NPHP4</italic> with autosomal recessive inheritance since his asymptomatic parents each had a single heterozygous missense mutation of <italic>NPHP4</italic>. In conclusion, MRI and immunohistochemical analysis of renal biopsy specimens may be useful for evaluation of this disease.
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