CUBN gene mutations may cause focal segmental glomerulosclerosis (FSGS) in children

Background Imerslund-Gräsbeck Syndrome (IGS) is mainly caused by CUBN gene biallelic mutations. Proteinuria accompanies IGS specific symptoms in about half of the patients, isolated proteinuria is rarely reported. Here we present 3 patients with isolated proteinuria and focal segmental glomerulosclerosis (FSGS) caused by CUBN gene biallelic pathogenic variants. Method Whole exome sequencing was performed on three children with isolated proteinuria. CUBN gene biallelic pathogenic variants were found and then verified by sanger sequencing. Their clinical, pathological and molecular genetic characteristics were analyzed and correlated accordingly. Results All three children presented with isolated proteinuria, no megaloblastic anemia. Their urine levels of β2 microglobulin were normal or slightly higher. Renal biopsies showed focal segmental glomerulosclerosis with mild glomerular mesangial hypercellularity, partial effacement of foot processes and podocyte microvillation. Two of them were found to carry compound heterozygous mutations and one homozygous mutation of CUBN gene. Totally four CUBN gene biallelic pathogenic variants were identified, including c.9287 T > C (p.L3096P), c.122 + 1G > A, c.7906C > T (p.R2636*), c.10233G > A (p.W3411*). Except for intron splice-site mutation, all other variants are located in highly conserved sites of CUB domain for binding to albumin. Conclusion The results demonstrate that CUBN gene mutations may cause isolated proteinuria pathologically presented as FSGS. Our cases extend the spectrum of renal manifestation and genotype of CUBN gene mutations.

Urinary coenzyme Q10 as a diagnostic biomarker and predictor of remission in a patient with ADCK4-associated Glomerulopathy: a case report

Background AarF domain-containing kinase 4 (ADCK4)-associated glomerulopathy is a mitochondrial nephropathy caused by mutations in the ADCK4 gene, which disrupt coenzyme Q10 biosynthesis. Case presentation We report the case of a 25-year-old female patient with ADCK4-associated glomerulopathy presenting with proteinuria (and with no additional systemic symptoms). A known missense substitution c.737G > A (p.S246N) and a novel frameshift c.577-600del (p.193-200del) mutation were found. We followed the patient for 24 months during supplementation with coenzyme Q10 (20 mg/kg/d – 30 mg/kg/d) and describe the clinical course. In addition, we measured serum and urine coenzyme Q10 levels before and after coenzyme Q10 supplementation and compared them with those of healthy control subjects. The patient’s urinary coenzyme Q10 to creatinine ratio was higher than that of healthy controls before coenzyme Q10 supplementation, but decreased consistently with proteinuria after coenzyme Q10 supplementation. Conclusions Although the use of urinary coenzyme Q10 as a diagnostic biomarker and predictor of clinical remission in patients with ADCK4-associated glomerulopathy should be confirmed by larger studies, we recommend measuring urinary coenzyme Q10 in patients with isolated proteinuria of unknown cause, since it may provide a diagnostic clue to mitochondrial nephropathy.

Early-onset COQ8B (ADCK4) glomerulopathy in a child with isolated proteinuria: a case report and literature review

Background Herein, a 3-year-old boy presented with hidden-onset isolated proteinuria was reported. The disease was induced by COQ8B (previously termed ADCK4) compound heterozygous variants, including c.[271C > T] and c.[737G > A], which were inherited from his father and mother, respectively. Case presentation The patient visited our clinic due to non-nephrotic range proteinuria for 3 months, but no obvious abnormality was detected in the vital signs or laboratory test results. Renal histopathology revealed mitochondrial nephropathy, which manifested as mild glomerular abnormalities under light microscope, together with mitochondrial proliferation and hypertrophy and crowded arrangement under electron microscope. As suggested by whole exome sequencing, the patient inherited the COQ8B compound heterozygous variants from both of his parents who showed normal phenotype. After literature review, it was confirmed that one of the variant site (c.[271C > T]) had not been reported among the East Asian populations so far. Conclusions Steroid-resistant nephrotic syndrome and focal segmental glomerulosclerosis are the most common phenotypes and renal histopathological manifestations of COQ8B variant. Nonetheless, our case shows that such variant may have hidden and mild clinical manifestations at the early onset. Therefore, early diagnosis will help to identify children at the early disease stage who have opportunity to benefit from oral coenzyme Q10 supplementation.

P1701ANTIBODY MEDIATED REJECTION: CLINICAL PHENOTYPE MATTERS

Background and Aims Protocol biopsies following kidney transplantation (KT) allow the histological diagnosis of antibody-mediated rejection (ABMR) with stable renal function (RF). Controversy arises when considering isolated proteinuria as a clinical biomarker. Currently, there is no effective treatment for ABMR and transplant units may decide on treatment independently of the clinical expression. Method KT recipients (1987-2017) with post-KT biopsies (2008-2018) showing ABMR graft lesions (category 2-Banff’2015) >1year post-KT were included. Cases were grouped into phenotypes of ABMR according to the clinical picture at biopsy : 1) acute RF impairment (↑creatinine >15% three weeks before biopsy) with/without proteinuria and with/without DSA detection. 2) sub-acute RF impairment (↑creatinine >15% six months before biopsy) with/without proteinuria and with/without DSA detection, 3) performed for DSA detection with stable RF and no proteinuria or 4) protocol biopsy, with stable RF, no proteinuria or DSA detection. We considered an additional category: 5) isolated proteinuria (↑>500 mg or x2 six months before biopsy). Categories 1), 2) and 5) were considered clinical ABMR. Categories 3) and 4) were considered subclinical ABMR. We aimed to evaluate graft outcomes in the different ABMR phenotypes. Results In a cohort of 105 KT recipients with histologic lesions of ABMR, biopsies corresponded to phenotypes 1) in 35 (33%), 2) 10 (9,5%), 3) 21 (20,3%), 4) 14 (13,4%) and y 5) in 25 23,8%). No differences between clinical and subclinical ABMR were found in baseline characteristics except for donors ‘age, who were older within the clinical group (51.8±18.8 vs. 43.88 ±16.1; p=0.04). At time of biopsy, subclinical had better RF than clinical ABMR (creatinine 1.3±0.4 mg/dl vs. 2.2±1.1 mg/dl; p=0.02) and less proteinuria (161 mg/g [IQR 93-269] vs 939 mg/g [IQR 412-2000]; p=0.001) Graft survival was worse in those patients with acute and sub-acute RF impairment, followed by those with isolated proteinuria (Figure 1). In comparison to subclinical ABMR, those with RF impairment and isolated proteinuria had an increased risk of graft lost; HR 9.4 (95% IC 2.2-40.7, p=0.002) and 4.8 (95% IC 1.01-23.2, P=0.05) respectively. DSA detection in these groups did not impact graft survival. Specific treatment was not different among groups, except for steroid pulses, which were more frequently applied in cases of ABMR with clinical manifestation. Conclusion The clinical phenotypes of ABMR influence long-term graft survival independently from treatment. Understanding graft evolution according to clinical phenotype at the time of histologic diagnosis should guide the therapeutic strategy, to balance risk-benefit ratio.