A mother and daughter with unexplained renal failure

Significance of kidney biopsy in autosomal dominant tubulointerstitial kidney disease-UMOD: is kidney biopsy truly nonspecific?

Background

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is a rare hereditary disease caused by a variety of genetic mutations. Carriers of a mutation in the responsible genes are at risk of reaching end-stage kidney disease typically in middle age. The frequency of this disease is assumed to be underestimated because of a lack of disease-specific signs. Pathological findings obtained from kidney of uromodulin related ADTKD (ADTKD-UMOD) patients are regarded as non-specific and less-informative for its diagnosis. This research was undertaken to evaluate the significance of kidney biopsy in ADTKD-UMOD patients.

Methods

Thirteen patients from 10 families with nine identified uromodulin (UMOD) gene mutations who underwent kidney biopsy in the past were studied. Their kidney tissues were stained with anti-UMOD antibody in addition to conventional methods such as PAS staining. When positive, the numbers of tubules with visible UMOD protein accumulations were calculated based on the total numbers of UMOD expressing tubules. Pathological findings such as tubulointerstitial fibrosis, atrophy, inflammation and glomerulosclerosis were also evaluated and analyzed.

Results

Interstitial fibrosis and tubular atrophy were present in all 13 patients. Most atrophic tubules with thickening and lamellation of tubular basement membranes showed negative UMOD staining. In all but two patients with C94F mutations, massive accumulation of UMOD proteins was observed in the renal endoplasmic reticulum. UMOD accumulations were also detectable by PAS staining as polymorphic unstructured materials in the 11 patients at frequencies of 2.6–53.4%. 80.4% of the UMOD accumulations were surrounded by halos. The detection rate of UMOD accumulations positively correlated with eGFR. Glomerulosclerosis was detected in 11/13 patients, with a frequency of 20.0 to 61.1%, while no cystic dilatations of glomeruli were detected.

Conclusions

Massively accumulated UMOD proteins in ADTKD-UMOD kidneys are detectable not only by immunostaining using anti-UMOD antibody but also by conventional methods such as PAS staining, although their detection is not easy. These findings can provide important clues to the diagnosis of ADTKD-UMOD. Kidney biopsy in ADTKD-UMOD may be more informative than assumed previously.

The renal biopsy in the genomic era

Renal biopsy was introduced in the 1950s. By 1980 the pathologic diagnostic criteria for the majority of medical kidney diseases known today, including pediatric diseases, were established using light, electron microscopy and immunohistochemistry. However, it has become clear that there are limitations in the morphologic evaluation, mainly because a given pattern of injury can be caused by different aetiologies and, conversely, a single aetiology may present with more than one histological pattern. An explosion in kidney disease research in the last 20-30 years has brought new knowledge from bench to bedside rapidly and resulted in new molecular and genetic tools that enhance the diagnostic and prognostic power of the renal biopsy. Genomic technologies such as polymerase chain reaction (PCR), in situ hybridization and oligonucleotide microarrays, collectively known as genomics, detect single or multiple genes underscoring the pathologic changes and revealing specific causes of injury that may require different treatment. The aims of this review are to (1) summarize current recommendations for diagnostic renal biopsies encompassing light microscopy, immunofluorescence or immunohistochemistry and electron microscopy; (2) address the limitations of morphology; (3) show current contributions of genomic technologies adjunct to the renal biopsy, and provide examples of how these may transform pathologic interpretation into molecular disease phenotypes.