AJKD Atlas of Renal Pathology: Fabry nephropathy

Genetic Susceptibility to Chronic Kidney Disease: Links, Risks and Management

Chronic kidney disease (CKD) is associated with significant morbidity and mortality worldwide. In recent years, our understanding of genetic causes of CKD has expanded significantly with several renal conditions having been identified. This review discusses the current landscape of genetic kidney disease and their potential treatment options. This review will focus on cystic kidney disease, glomerular disease with genetic associations, congenital anomalies of kidneys and urinary tract (CAKUT), autosomal dominant-tubulointerstitial kidney disease (ADTKD), inherited nephrolithiasis and nephrocalcinosis.

A Case of a 49-Year-Old Man with Nonclassical Fabry Disease Diagnosed by Renal Biopsy

Fabry disease (FD) is a rare X-linked lysosomal storage disorder caused by mutations in the galactosidase A (GLA) gene that result in deficiency of α-GLA activity, leading to major organ failure and premature mortality. According to different disease courses, FD can be divided into classical and nonclassical phenotypes. The nonclassical FD phenotype is always absent of characteristic symptoms, which makes identifying it challenging. This article presents a 49-year-old man with a 10-year history of proteinuria and decreased glomerular filtration rate. An electrocardiogram showed a complete right bundle branch block and abnormal Q waves in high lateral, accompanied by dramatically elevated ST segment. Consequently, a renal biopsy was performed. Vacuolation was found in many podocytes in light microscopic examinations. Similarly, a myelin-like structure was detected by electron microscopy. Pathological findings were most consistent with FD. Consequently, genetic analysis, p.R301Q (c.902G>A [p.Arg301Gln]), confirmed the FD diagnosis. Angiotensin receptor blocker and traditional Chinese medicine, but not enzyme replacement therapy, were prescribed due to financial constraints. The patient had stabilization of kidney disease 6 months later. The case showed that renal biopsy should be performed in patients with cardiac and renal symptoms, which could contribute toward the correct diagnosis for nonclassical FD type.

Defective lysosomal storage in Fabry disease modifies mitochondrial structure, metabolism and turnover in renal epithelial cells

Fabry disease (FD) is an X-linked lysosomal storage disorder. Deficiency of the lysosomal enzyme alpha-galactosidase (GLA) leads to accumulation of potentially toxic globotriaosylceramide (Gb3) on a multisystem level. Cardiac and cerebrovascular abnormalities as well as progressive renal failure are severe, life-threatening long-term complications. The complete pathophysiology of chronic kidney disease (CKD) in FD and the role of tubular involvement for its progression are unclear. We established human renal tubular epithelial cell lines from the urine of male FD patients and male controls. The renal tubular system is rich in mitochondria and involved in transport processes at high-energy costs. Our studies revealed fragmented mitochondria with disrupted cristae structure in FD patient cells. Oxidative stress levels were elevated and oxidative phosphorylation was upregulated in FD pointing at enhanced energetic needs. Mitochondrial homeostasis and energy metabolism revealed major changes as evidenced by differences in mitochondrial number, energy production and fuel consumption. The changes were accompanied by activation of the autophagy machinery in FD. Sirtuin1, an important sensor of (renal) metabolic stress and modifier of different defense pathways, was highly expressed in FD. Our data show that lysosomal FD impairs mitochondrial function and results in severe disturbance of mitochondrial energy metabolism in renal cells. This insight on a tissue-specific level points to new therapeutic targets which might enhance treatment efficacy.

LMX1B-associated nephropathy that showed myelin figures on electron microscopy

The mutation of LIM homeodomain transcription factor LMX1B gene leads to nail-patella syndrome (NPS), which is characterized by dysplastic nails, hypoplastic patellae, iliac horns and nephropathy. The characteristic renal histological finding of NPS nephropathy is irregular thickening of the glomerular basement membrane with patchy lucent areas, including deposits of bundles of type III collagen fibrils revealed by electron microscopy (EM). Fabry disease is a lysosomal storage disorder caused by a deficiency of α-galactosidase A activity, and the characteristic EM finding is a lamellated membrane structure (myelin figures). We present the case of a male with LMX1B-associated nephropathy (LAN) who showed focal segmental glomerulosclerosis (FSGS) on light microscopy, and myelin figures and slight deposits of collagen fibrils on EM, without findings of glomerular basement membrane abnormality suggestive for NPS. A 21-year-old Japanese-Brazilian man was admitted to hospital for an investigation of the cause of proteinuria and decreased renal function. A renal biopsy was performed to investigate the cause of renal damage. Fabry disease was initially considered, based on the presence of myelin figures on EM, but since he had normal α-galactosidase A activity, this initial diagnosis was denied, and the patient was subsequently diagnosed with FSGS. At 22 years after that renal biopsy, the patient was incidentally diagnosed with LAN when NM_002316:3c.746G > A:p.(Arg249Gln) LMX1B variant was identified in his older brother by a pre-transplantation examination, and the same mutation was confirmed in the patient. Myelin figures revealed by EM might become one of the clues for the diagnosis of LAN.

Renal Manifestations of Fabry Disease: A Narrative Review

Purpose of review

In this narrative review, we describe general aspects, histological alterations, treatment, and implications of Fabry disease (FD) nephropathy. This information should be used to guide physicians and patients in a shared decision-making process.

Source of information

Original peer-reviewed articles, review articles, and opinion pieces were identified from PubMed and Google Scholar databases. Only sources in English were accessed.

Methods

We performed a focused narrative review assessing the main aspects of FD nephropathy. The literature was critically analyzed from a theoretical and contextual perspective, and thematic analysis was performed.

Key findings

FD nephropathy is related to the progressive accumulation of GL3, which occurs in all types of renal cells. It is more prominent in podocytes, which seem to play an important role in the pathogenesis of this nephropathy. A precise detection of renal disorders is of fundamental importance because the specific treatment of FD is usually delayed, making reversibility unlikely and leading to a worse prognosis.

Limitations

As no formal tool was applied to assess the quality of the included studies, selection bias may have occurred. Nonetheless, we have attempted to provide a comprehensive review on the topic using current studies from experts in FD and extensive review of the literature.

Myelin bodies in LMX1B-associated nephropathy: potential for misdiagnosis

BACKGROUND

Myelin figures, or zebra bodies, seen on electron microscopy were historically considered pathognomonic of Fabry disease, a rare lysosomal storage disorder caused by alpha-galactosidase A deficiency and associated with X-linked recessive mode of inheritance. More recently, iatrogenic phospholipidosis has emerged as an important alternate cause of myelin figures in the kidney.

METHODS

We report two families with autosomal dominant nephropathy presenting with proteinuria and microscopic hematuria, and the kidney biopsies were notable for the presence of myelin figures and zebra bodies.

RESULTS

Laboratory and genetic work-up for Fabry disease was negative. Genetic testing in both families revealed the same heterozygous missense mutation in LMX1B (C.737G>A, p.Arg246Gln). LMX1B mutations are known to cause nail-patella syndrome, featuring dysplastic nails and patella with or without nephropathy, as well as isolated LMX1B-associated nephropathy in the absence of extrarenal manifestations.

CONCLUSIONS

LMX1B mutation-associated nephropathy should be considered in hereditary cases of proteinuria and/or hematuria, even in the absence of unique glomerular basement membrane changes indicative of nail-patella syndrome. In addition, LMX1B mutation should be included in the differential diagnosis of myelin figures and zebra bodies on kidney biopsy, so as to avoid a misdiagnosis.

A case of female Fabry disease revealed by renal biopsy

Fabry disease (FD) is an X-linked inherited glycosphingolipid metabolism disorder, therefore, heterozygous female FD patients display highly variable clinical symptoms, disease severity, and pathological findings. This makes it very challenging to diagnosing female patients with FD. A 69-year-old Japanese female was introduced to the nephrologist for the evaluation of proteinuria. A renal biopsy was performed. Although the light microscopic examinations revealed that most of the glomeruli showed minor glomerular abnormalities, however, vacuolation was apparently found in the tubular epithelial cells. Immunofluorescence staining for globotriaosylceramide was positively detected in some podocytes and distal tubular epithelial cells. In addition, myelin-like structure (zebra body) was detected by electron microscopy. Pathological findings were most consistent with FD. Consequently, biochemical and genetic analysis confirmed the diagnosis of female FD. Enzyme replacement therapy was performed in conjunction with renin-angiotensin aldosterone system inhibitors and beta-blockers. The patient's family members received the analysis, and the same DNA missense mutation was detected in the patient's grandson. The enzyme replacement therapy was introduced to the grandson. The present case showed that renal biopsy can contribute towards a correct diagnosis for FD. Particularly, in female FD patients, careful examination of pathological changes is essential, for example, vacuolation of any type of renal cells may be a clue for the diagnosis.

TFEB-driven lysosomal biogenesis is pivotal for PGC1α-dependent renal stress resistance

Because injured mitochondria can accelerate cell death through the elaboration of oxidative free radicals and other mediators, it is striking that proliferator γ coactivator 1-α (PGC1α), a stimulator of increased mitochondrial abundance, protects stressed renal cells instead of potentiating injury. Here, we report that PGC1α’s induction of lysosomes via transcription factor EB (TFEB) may be pivotal for kidney protection. CRISPR and stable gene transfer showed that PGC1α-KO tubular cells were sensitized to the genotoxic stressor cisplatin, whereas Tg cells were protected. The biosensor mitochondrial-targeted Keima (mtKeima) unexpectedly revealed that cisplatin blunts mitophagy both in cells and mice. PGC1α and its downstream mediator NAD⁺ counteracted this effect. PGC1α did not consistently affect known autophagy pathways modulated by cisplatin. Instead RNA sequencing identified coordinated regulation of lysosomal biogenesis via TFEB. This effector pathway was sufficiently important that inhibition of TFEB or lysosomes unveiled a striking harmful effect of excess PGC1α in cells and conditional mice. These results uncover an unexpected effect of cisplatin on mitophagy and PGC1α’s reliance on lysosomes for kidney protection. Finally, the data illuminate TFEB as a potentially novel target for renal tubular stress resistance.

PGC1α is renoprotective in the setting of platinum-based chemotherapy through the induction of mitophagy and lysosomal biogenesis via transcription factor EB.

Clinical parameters, LysoGb3, podocyturia, and kidney biopsy in children with Fabry disease: is a correlation possible?

BACKGROUND

Fabry disease is an X-linked lysosomal storage disorder caused by α-galactosidase enzyme deficiency. We present clinical, biochemical, and histologic findings in children with classical phenotypic presentation of Fabry disease.

METHODS

A retrospective analysis was performed using charts from 14 children with confirmed diagnosis. Clinical parameters were evaluated. Globotriaosylsphingosine -lysoGb3- detection in plasma, podocyturia, and kidney biopsy were carried out in all cases.

RESULTS

All patients except one demonstrated at least one symptom of Fabry disease. LysoGb3 levels were above the normal range in all patients. Podocyturia was documented in all patients. Kidney biopsy revealed glomerular, interstitial, vascular, and tubular changes on light microscopy in nearly all patients. Electron microscopy showed podocyte inclusions in all patients.

CONCLUSIONS

No difference in symptomatology was discernible between boys and girls. Podocyturia was detectable in children serving as a possible early marker of kidney injury. LysoGb3 was elevated in all cases, emphasizing the importance for diagnosis especially in female patients with normal αGal A activity. A possible association between lysoGb3 and symptom severity and histological involvement in kidney biopsy should be assessed in prospective studies with enough statistical power to determine if lysoGb3 can be used to predict nephropathy in children with Fabry disease.