A comparison of the ocular features in Pierson and Alport syndrome: a case report and literature review

BACKGROUND

Pierson syndrome and X-linked Alport syndrome result from pathogenic variants in LAMB2 and COL4A5, respectively, and both affect basement membranes in the kidney and the eye. This study describes the ocular features in an individual with a homozygous LAMB2 pathogenic variant and compares the reported abnormalities in Pierson syndrome with those in Alport syndrome.

METHODS

A 28-year-old man who developed kidney failure 10 years previously and subsequently had an atrial septal defect repair was suspected of having genetic kidney disease on the basis of his likely diagnosis of Focal and Segmental Glomerulosclerosis (FSGS), his young age at presentation, and his cardiac anomaly. He then underwent Whole Exome Sequencing and a formal ophthalmological examination.

RESULTS

The patient was found to have a homozygous Likely Pathogenic missense variant (p.(Arg1719Cys)) in LAMB2 consistent with the diagnosis of Pierson syndrome. He had normal visual acuity, normal optic globe and cornea size, and normal lens appearance on direct examination. Upon further testing, his cornea demonstrated central thinning. There was also increased corneal endothelial pleomorphism, a reduced foveal reflex, and a blunted foveal curvature, similar to the features seen in X-linked Alport syndrome.

CONCLUSION

Our patient had a later onset form of Pierson syndrome or "FSGS type 5, with or without ocular abnormalities," consistent with his "milder" LAMB2 missense variant. The resemblance of the ocular features in Pierson syndrome and X-linked Alport syndrome suggests that mutations in LAMB2 and COL4A5 have similar effects on basement membranes and the pathogenesis of ocular damage.

Global coagulation assays in patients with chronic kidney disease and their role in predicting thrombotic risk

BACKGROUND

Despite cardiovascular diseases and thrombosis being major causes of death in patients with chronic kidney disease (CKD), there remains no effective biomarker to predict thrombotic risk in this population.

OBJECTIVE

To evaluate global coagulation assays in patients with CKD and correlate the biomarkers to clinical outcomes.

MATERIAL AND METHODS

Patients with eGFR<30 mL/min/1.73m² were recruited (n = 90) in this prospective observational study. Blood samples were collected for global coagulation assays, including thromboelastography, calibrated automated thrombogram (CAT), overall hemostatic potential (OHP) and tissue factor pathway inhibitor (TFPI).

RESULTS

Following adjustment for age and gender, CKD subjects (mean age 66 years, 36 % female) had increased maximum amplitude on thromboelastography (70.1 vs 60.2 mm, p < 0.001), higher peak thrombin (233.2 vs 219.7 mm, p = 0.030) and increased OHP (16.1 vs 6.4 units, p < 0.001) compared to healthy controls (n = 153). TFPI was also increased in CKD patients (36.4 vs 14.5 ng/mL, p < 0.001). Compared to hemodialysis patients (n = 43), peritoneal-dialysis patients (n = 25) had more hypercoagulable parameters. Thirty-five CKD patients reported thrombotic complications - key predictors included dialysis, higher fibrinogen, reduced endogenous thrombin potential, elevated D-dimer and increased TFPI. Using the dialysis cohort, the predictive risk model based on the key predictors performed better than Framingham heart score and number of cardiovascular risk factors (Harrell's C-stat 0.862 vs 0.585 vs 0.565).

CONCLUSION

CKD appears to confer a hypercoagulable state compared to healthy controls. Interestingly, reduced thrombin generation and raised TFPI was paradoxically associated with increased thrombotic risks, highlighting possible complex compensatory mechanisms within the coagulation system, which may be important in predicting clinical outcomes.

Increased retinal drusen in IgA glomerulonephritis are further evidence for complement activation in disease pathogenesis

Drusen are retinal deposits comprising cell debris, immune material and complement that are characteristic of macular degeneration but also found in glomerulonephritis. This was a pilot cross-sectional study to determine how often drusen occurred in IgA glomerulonephritis and their clinical significance. Study participants underwent non-mydriatic retinal photography, and their deidentified retinal images were examined for drusen by two trained graders, who compared central drusen counts, counts ≥ 10 and drusen size with those of matched controls. The cohort comprised 122 individuals with IgA glomerulonephritis including 89 males (73%), 49 individuals (40%) of East Asian or Southern European ancestry, with an overall median age of 54 years (34-64), and median disease duration of 9 years (4-17). Thirty-nine (33%) had an eGFR < 60 ml/min/1.73 m² and 72 had previously reached kidney failure (61%). Overall mean drusen counts were higher in IgA glomerulonephritis (9 ± 27) than controls (2 ± 7, p < 0.001). Central counts ≥ 10 were also more common (OR = 3.31 (1.42-7.73, p = 0.006), and were associated with longer disease duration (p = 0.03) but not kidney failure (p = 0.31). Larger drusen were associated with more mesangial IgA staining (p = 0.004). Increased drusen counts were also present in IgA glomerulonephritis secondary to Crohn's disease but not with Henoch-Schonlein purpura. The finding of retinal drusen in IgA glomerulonephritis is consistent with complement activation and represents a model for better understanding glomerular immune deposition and a supporting argument for treatment with anti-complement therapies.

Retinal drusen are more common and larger in SLE with renal impairment

Introduction

Complement has been implicated in systemic lupus erythematosus (SLE) pathogenesis on the basis of the associations with inherited complement defects and genome-wide association study risk alleles, glomerular deposits, reduced serum levels, and occasional reports of retinal drusen. This study examined drusen in SLE and their clinical significance.

Methods

This cross-sectional observational study compared individuals with SLE recruited from renal and rheumatology clinics with hospital controls. Participants were reviewed for clinical features and underwent imaging with a nonmydriatic retinal camera. Deidentified images were examined by 2 trained graders for drusen number and size using a grid overlay.

Results

The cohort with SLE (n = 65) comprised 55 women (85%) and 10 men (15%) with a median age of 47 years (interquartile range 35–59), where 23 (35%) were of southern European or Asian ancestry, and 32 (49%) had biopsy-proven lupus nephritis. Individuals with SLE had higher mean drusen numbers than controls (27 ± 60, 3 ± 9, respectively, P = 0.001), more drusen counts ≥10 (31, 48% and 3, 5%, respectively, P < 0.001), and more medium-large drusen (14, 22% and 3, 5%, respectively, P < 0.001). In SLE, mean drusen counts were higher, and drusen were larger, with an estimated glomerular filtration rate (eGFR) <90 ml/min per 1.73 m² (P = 0.02, P = 0.02, respectively) or class IV nephritis (P = 0.03, P = 0.02).

Conclusion

Drusen composition resembles that of glomerular immune deposits. CFH controls complement activation in the extracellular matrix and CFH risk variants are shared by drusen in macular degeneration and by SLE. CFH represents a possible treatment target for SLE especially with renal impairment.

Nox-4 deletion reduces oxidative stress and injury by PKC-α-associated mechanisms in diabetic nephropathy

Current treatments for diabetic nephropathy (DN) only result in slowing its progression, thus highlighting a need to identify novel targets. Increased production of reactive oxygen species (ROS) is considered a key downstream pathway of end-organ injury with increasing data implicating both mitochondrial and cytosolic sources of ROS. The enzyme, NADPH oxidase, generates ROS in the kidney and has been implicated in the activation of protein kinase C (PKC), in the pathogenesis of DN, but the link between PKC and Nox-derived ROS has not been evaluated in detail in vivo. In this study, global deletion of a NADPH-oxidase isoform, Nox4, was examined in mice with streptozotocin-induced diabetes (C57Bl6/J) in order to evaluate the effects of Nox4 deletion, not only on renal structure and function but also on the PKC pathway and downstream events. Nox4 deletion attenuated diabetes-associated increases in albuminuria, glomerulosclerosis, and extracellular matrix accumulation. Lack of Nox4 resulted in a decrease in diabetes-induced renal cortical ROS derived from the mitochondria and the cytosol, urinary isoprostanes, and PKC activity. Immunostaining of renal cortex revealed that major isoforms of PKC, PKC-α and PKC-β1, were increased with diabetes and normalized by Nox4 deletion. Downregulation of the PKC pathway was observed in tandem with reduced expression of vascular endothelial growth factor (VEGF), transforming growth factor (TGF)-β1 and restoration of the podocyte slit pore protein nephrin. This study suggests that deletion of Nox4 may alleviate renal injury via PKC-dependent mechanisms, further strengthening the view that Nox4 is a suitable target for renoprotection in diabetes.

Genetic targeting or pharmacologic inhibition of NADPH oxidase nox4 provides renoprotection in long-term diabetic nephropathy

Diabetic nephropathy may occur, in part, as a result of intrarenal oxidative stress. NADPH oxidases comprise the only known dedicated reactive oxygen species (ROS)-forming enzyme family. In the rodent kidney, three isoforms of the catalytic subunit of NADPH oxidase are expressed (Nox1, Nox2, and Nox4). Here we show that Nox4 is the main source of renal ROS in a mouse model of diabetic nephropathy induced by streptozotocin administration in ApoE(-/-) mice. Deletion of Nox4, but not of Nox1, resulted in renal protection from glomerular injury as evidenced by attenuated albuminuria, preserved structure, reduced glomerular accumulation of extracellular matrix proteins, attenuated glomerular macrophage infiltration, and reduced renal expression of monocyte chemoattractant protein-1 and NF-κB in streptozotocin-induced diabetic ApoE(-/-) mice. Importantly, administration of the most specific Nox1/4 inhibitor, GKT137831, replicated these renoprotective effects of Nox4 deletion. In human podocytes, silencing of the Nox4 gene resulted in reduced production of ROS and downregulation of proinflammatory and profibrotic markers that are implicated in diabetic nephropathy. Collectively, these results identify Nox4 as a key source of ROS responsible for kidney injury in diabetes and provide proof of principle for an innovative small molecule approach to treat and/or prevent chronic kidney failure.

Role of Nox2 in diabetic kidney disease

NADPH oxidase (Nox) isoforms have been implicated in contributing to diabetic microvascular complications, but the functional role of individual isoforms in diabetic kidney are unclear. Nox2, in particular, is highly expressed in phagocytes and may play a key inflammatory role in diabetic kidney disease. To determine the role of Nox2, we evaluated kidney function and pathology in wild-type (WT; C57BL/6) and Nox2 knockout (KO) mice with type 1 diabetes. Diabetes was induced in male Nox2 KO and WT mice with a multiple low-dose streptozotocin protocol. Groups were studied for kidney disease after 8 and 20 wk of diabetes. Hyperglycemia and body weights were similar in WT and Nox2 KO diabetic mice. All functional and structural features of early and later stage diabetic kidney disease (albuminuria, mesangial matrix, tubulointerstitial disease, and gene expression of matrix and transforming growth factor-β) were similar in both diabetic groups compared with their respective nondiabetic groups, except for reduction of macrophage infiltration and monocyte chemoattractant protein-1 in the diabetic Nox2 KO mice. Systolic blood pressure by telemetry was surprisingly increased in Nox2 KO mice; however, the systolic blood pressure was reduced in the diabetic WT and Nox2 KO mice by tail-cuff. Interestingly, diabetic Nox2 KO mice had marked upregulation of renal Nox4 at both the glomerular and cortical levels. The present results demonstrate that lack of Nox2 does not protect against diabetic kidney disease in type 1 diabetes, despite a reduction in macrophage infiltration. The lack of renoprotection may be due to upregulation of renal Nox4.

Post-stroke inhibition of induced NADPH oxidase type 4 prevents oxidative stress and neurodegeneration

Ischemic stroke is the second leading cause of death worldwide. Only one moderately effective therapy exists, albeit with contraindications that exclude 90% of the patients. This medical need contrasts with a high failure rate of more than 1,000 pre-clinical drug candidates for stroke therapies. Thus, there is a need for translatable mechanisms of neuroprotection and more rigid thresholds of relevance in pre-clinical stroke models. One such candidate mechanism is oxidative stress. However, antioxidant approaches have failed in clinical trials, and the significant sources of oxidative stress in stroke are unknown. We here identify NADPH oxidase type 4 (NOX4) as a major source of oxidative stress and an effective therapeutic target in acute stroke. Upon ischemia, NOX4 was induced in human and mouse brain. Mice deficient in NOX4 (Nox4(-/-)) of either sex, but not those deficient for NOX1 or NOX2, were largely protected from oxidative stress, blood-brain-barrier leakage, and neuronal apoptosis, after both transient and permanent cerebral ischemia. This effect was independent of age, as elderly mice were equally protected. Restoration of oxidative stress reversed the stroke-protective phenotype in Nox4(-/-) mice. Application of the only validated low-molecular-weight pharmacological NADPH oxidase inhibitor, VAS2870, several hours after ischemia was as protective as deleting NOX4. The extent of neuroprotection was exceptional, resulting in significantly improved long-term neurological functions and reduced mortality. NOX4 therefore represents a major source of oxidative stress and novel class of drug target for stroke therapy.

Receptor for advanced glycation end products (RAGE) deficiency attenuates the development of atherosclerosis in diabetes

OBJECTIVE

Activation of the receptor for advanced glycation end products (RAGE) in diabetic vasculature is considered to be a key mediator of atherogenesis. This study examines the effects of deletion of RAGE on the development of atherosclerosis in the diabetic apoE(-/-) model of accelerated atherosclerosis.

RESEARCH DESIGN AND METHODS

ApoE(-/-) and RAGE(-/-)/apoE(-/-) double knockout mice were rendered diabetic with streptozotocin and followed for 20 weeks, at which time plaque accumulation was assessed by en face analysis.

RESULTS

Although diabetic apoE(-/-) mice showed increased plaque accumulation (14.9 +/- 1.7%), diabetic RAGE(-/-)/apoE(-/-) mice had significantly reduced atherosclerotic plaque area (4.9 +/- 0.4%) to levels not significantly different from control apoE(-/-) mice (4.3 +/- 0.4%). These beneficial effects on the vasculature were associated with attenuation of leukocyte recruitment; decreased expression of proinflammatory mediators, including the nuclear factor-kappaB subunit p65, VCAM-1, and MCP-1; and reduced oxidative stress, as reflected by staining for nitrotyrosine and reduced expression of various NADPH oxidase subunits, gp91phox, p47phox, and rac-1. Both RAGE and RAGE ligands, including S100A8/A9, high mobility group box 1 (HMGB1), and the advanced glycation end product (AGE) carboxymethyllysine were increased in plaques from diabetic apoE(-/-) mice. Furthermore, the accumulation of AGEs and other ligands to RAGE was reduced in diabetic RAGE(-/-)/apoE(-/-) mice.

CONCLUSIONS

This study provides evidence for RAGE playing a central role in the development of accelerated atherosclerosis associated with diabetes. These findings emphasize the potential utility of strategies targeting RAGE activation in the prevention and treatment of diabetic macrovascular complications.

Use of magnetic resonance imaging to assess renal structure and function in reflux nephropathy

AIM

Despite numerous potential advantages, the role of magnetic resonance imaging (MRI) in depicting structural and functional abnormalities in kidney disease has not been well addressed. In reflux nephropathy in particular, nuclear scintigraphy (NS) has become the diagnostic gold standard, however, other imaging modalities may be required for adequate clinical appraisal. We therefore assessed the use of MRI in reflux nephropathy, comparing findings with those obtained using conventional imaging techniques.

METHODS

Eight women with likely or proven reflux nephropathy underwent MRI scanning with structural and split functional appraisal. Results were compared with those obtained with ultrasound and NS.

RESULTS

As expected, structural abnormalities were better defined with MRI than with ultrasound. NS findings were confirmed in most, but not all, MRI scans: NS and ultrasound had failed to identify scarring and cyst development in one patient. A close correlation was observed between MRI and NS renal functional estimates, regardless of whether whole kidney (r(2) = 0.87, P = 0001) or region of interest (r(2) = 0.99, P < 0001) techniques were used. Bland Altman plot analysis suggested methods were interchangeable.

CONCLUSION

MRI provided more accurate diagnostic information structurally than ultrasound and MRI and split renal functional estimates correlated well with NS. It achieved in one study what otherwise required additional scans and without the need for ionizing radiation. These results suggest it should be considered as a diagnostic tool for reflux nephropathy.

Diabetic nephropathy: from mechanisms to rational therapies

Diabetic nephropathy is a microvascular complication of diabetes. Specifically, it represents a major cause of morbidity and mortality in type 1 and type 2 diabetic subjects and has become the leading cause of end-stage renal disease in the Western world. Diabetic nephropathy appears to develop as a result of interactions between environmental insults and genetic susceptibility. Indeed, hyperglycemia is a clinical prerequisite for this complication, but it should be noted that only a subset of diabetic subjects will ultimately develop nephropathy. Over recent decades, cellular and molecular mechanisms underlying diabetic nephropathy have been increasingly delineated. In particular, diabetic kidney disease appears to occur as a result of the deleterious effects of both metabolic and hemodynamic insults, which at the cellular level lead to the activation of intracellular signaling pathways and transcription factors, thus triggering the production/release of cytokines, chemokines and growth factors, which mediate and/or amplify the renal damage. This ultimately leads to the structural and functional features characteristic of diabetic kidney disease. In the present review we summarize the evidence for key mediators of injury, which appear to be excellent treatment targets in diabetic nephropathy. The targets include various vasoactive hormones, the biochemical processes of the advanced glycation and protein kinase C. Furthermore, we review current and potentially new renoprotective therapies in the setting of diabetes.