Histomorphological and clinical characteristics of patients with thin glomerular basement membrane nephropathy.

BACKGROUND: Thin basement membrane nephropathy (TBMN) is a disorder characterized by ultrastructural abnormalities of the glomerular basement membrane (GBM), representing a spectrum of genetic and clinical phenotypes ranging from benign hematuria to proteinuria and chronic kidney disease. Recent studies have shown that a significant percentage of patients who initially present with hematuria later develop proteinuria and worsening renal function. MATERIALS AND METHODS: We retrospectively analyzed records of patients diagnosed with TBMN, including their clinical, laboratory, and histological features, in Slovenia from 2015 to 2020. RESULTS: TBMN was the main diagnosis at kidney biopsy in 34 (65%) of 52 included patients, while in 18 patients (35%) TBMN was diagnosed in addition to other renal diseases. In the isolated TBMN group, 29 of 34 patients had glomerulosclerosis (global, global and segmental, segmental only) accompanied by interstitial fibrosis/tubular atrophy of varying degrees. 13 patients with isolated TBMN had signs of advanced chronic kidney disease at the time of diagnosis, with estimated glomerular filtration rate < 60 mL/min/1.73m2. 29 patients had proteinuria, which exceeded 3 g/day in 4 patients. TBMN represents a proportion of patients with focal segmental glomerulosclerosis (FSGS) that have often been classified in the past as etiologically indeterminate FSGS. CONCLUSION: Ultrastructural examination showing diffuse thinning of the GBM is crucial for the TBMN diagnosis. TBMN was the main diagnosis of kidney biopsy in 2/3 of our patients, while it was accompanied by other renal diseases in 1/3. Up to 1/3 of patients with isolated TBMN had evidence of advanced chronic kidney disease at the time of diagnosis.