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HCV, HBV, and HIV associated with autoimmune kidney diseases
DISCUSSION
This case describes a child with rapidly progressive proteinuria and hematuria following a URI who was found to have VUS mutations in 3 different genes associated with chronic kidney disease. Serology tests on the patient were negative for streptococcal antibodies and antinuclear antibodies, ruling out poststreptococcal glomerulonephritis, or systemic lupus erythematosus. His renal biopsy findings were concerning for altered podocytes, mesangial cells, and basement membrane without inflammatory infiltrate, immune complex, complements, immunoglobulin A, or vasculopathy. His blood inflammatory markers, erythrocyte sedimentation rate, C-reactive protein, and ferritin were normal when his care team initiated daily steroids.
Overall, the patient’s clinical presentation and histopathology findings were suggestive of Alport syndrome or thin basement membrane nephropathy with a high potential to progress into FSGS.10-12 Alport syndrome affects 1 in 5000 to 10,000 children annually due to S-linked inheritance of COL4A5, or autosomal recessive inheritance of COL4A3 or COL4A4 genes. It presents with hematuria and hearing loss.10 Our patient had a single copy COL4A4 gene mutation that was classified as VUS. He also had 2 additional VUS affecting the TRPC6 and OSGEP genes. TRPC6 gene mutation can be associated with FSGS through autosomal dominant inheritance. Both COL4A4 and TRPC6 gene mutations were paternally inherited. Although the patient’s father not having renal disease argues against the clinical significance of these findings, there is literature on the potential role of heterozygous COL4A4 variant mimicking thin basement membrane nephropathy that can lead to renal impairment upon copresence of superimposed conditions.13 The patient’s rapidly progressing hematuria and changes in the basement membrane were worrisome for emerging FSGS. Furthermore, VUS of TRPC6 has been reported in late onset autosomal dominant FSGS and can be associated with early onset steroid-resistant nephrotic syndrome (NS) in children.14 This concern was voiced by 3 nephrology consultants during the initial evaluation, leading to the consensus that steroid treatment for podocytopathy would not alter the patient’s long-term outcomes (ie, progression to FSGS).
Immunomodulation
Our rationale for immunomodulatory treatment was based on the abrupt onset of renal concerns following a URI, suggesting the importance of an inflammatory trigger causing altered homeostasis in a genetically susceptible host. Preclinical models show that microbial products such as lipopolysaccharides can lead to podocytopathy by several mechanisms through activation of toll-like receptor signaling. It can directly cause apoptosis by downregulation of the intracellular Akt survival pathway.15 Lipopolysaccharide can also activate the NF-αB pathway and upregulate the production of interleukin-1 (IL-1) and TNF-α in mesangial cells.16,17
Both cytokines can promote mesangial cell proliferation.18 Through autocrine and paracrine mechanisms, proinflammatory cytokines can further perpetuate somatic tissue changes and contribute to the development of podocytopathy. For instance, TNF-α can promote podocyte injury and proteinuria by downregulation of the slit diaphragm protein expression (ie, nephrin, ezrin, or podocin), and disruption of podocyte cytoskeleton.19,20 TNF-α promotes the influx and activation of macrophages and inflammatory cells. It is actively involved in chronic alterations within the glomeruli by the upregulation of matrix metalloproteases by integrins, as well as activation of myofibroblast progenitors and extracellular matrix deposition in crosstalk with transforming growth factor and other key mediators.17,21,22
For the patient described in this case report, initial improvement on steroids encouraged the pursuit of additional treatment to downregulate inflammatory pathways within the glomerular milieu. However, within the COVID-19 environment, escalating the patient’s treatment using traditional immunomodulators (ie, calcineurin inhibitors or mycophenolate mofetil) was not favored due to the risk of infection. Initially, anakinra, a recombinant IL-1 receptor antagonist, was preferred as a steroid-sparing agent for its short life and safety profile during the pandemic. At first, the patient responded well to anakinra and was allowed a steroid wean when the dose was titrated up to 6 mg/kg daily. However, anakinra did not prevent the escalation of proteinuria following a URI. After the treatment was changed to adalimumab, a fully humanized monoclonal antibody to TNF-α, the patient continued to improve and reach full remission despite experiencing a cold and the flu in the following months.