Insights into the renal pathogenesis in Schimke immuno-osseous dysplasia: A renal histological characterization and expression analysis

Mechanisms of podocyte injury in genetic kidney disease

Glomerular diseases are a leading cause of chronic kidney disease worldwide. Both acquired and hereditary glomerulopathies frequently share a common final disease mechanism: disruption of the glomerular filtration barrier, podocyte injury, and ultimately podocyte death and detachment. Over 70 monogenic causes of proteinuric kidney disease have been identified, and most of these genes are highly expressed in podocytes, regulating key processes such as maintenance of the slit diaphragm, regulation of actin cytoskeleton remodeling, and modulation of downstream transcriptional pathways. Collectively, these are increasingly being referred to as hereditary "podocytopathies," in which podocyte injury is the central feature driving proteinuria and kidney dysfunction. In this review, we provide an overview of the monogenic podocytopathies and discuss the molecular mechanisms by which single-gene defects lead to podocyte injury and ultimately glomerulosclerosis. We review how advances in genomic technology and a better understanding of the cell biological basis of disease have led to the development of more targeted and personalized therapeutic strategies, including an overview of small molecule and gene therapy approaches.

When should the nephrologist think about genetics in patients with glomerular diseases?

This review discusses the significance of genetics in diagnosing glomerular diseases. Advances in genetic testing, particularly next-generation sequencing, have improved the accessibility and accuracy of diagnosing monogenic diseases, allowing for targeted gene panels and whole-exome/genome sequencing to identify genetic variants associated with glomerular diseases. Key indicators for considering a genetic cause include the age of onset, extrarenal features, family history, and inconclusive kidney biopsy results. Early-onset diseases, for instance, have a higher likelihood of being genetically caused, while extrarenal manifestations can also suggest an underlying genetic condition. A thorough family history can reveal patterns of inheritance that point to monogenic causes, although complexities like incomplete penetrance, skewed X inactivation and mosaicism can complicate the assessment. Also, autosomal recessive conditions imply asymptomatic parents, making genetic suspicion less likely, while de novo mutations can occur without any family history, further obscuring genetic assessment. Focal segmental glomerulosclerosis (FSGS) is characterized by podocyte injury and depletion, presenting in various forms, including primary, genetic, and secondary FSGS. Accurate classification of FSGS patients based on clinical and histological features is essential for guiding treatment decisions, optimizing therapeutic plans, avoiding unnecessary immunosuppression, and predicting relapse risk after kidney transplantation. Overall, a clinicopathological approach, enriched by genetic testing, offers a precise framework for diagnosis and management in glomerular diseases. Future directions for research and clinical practice include potential advancements in genetic testing and personalized medicine, which could further improve diagnostic precision and individualized treatment strategies.

Genetic and Clinical Features of Schimke Immuno-Osseous Dysplasia: Single-Centre Retrospective Study of 21 Unrelated Paediatric Patients over a Period of 20 Years

Schimke immuno-osseous dysplasia (SIOD) is a hereditary autosomal-recessive multi-system disorder with early mortality. It has variable clinical presentations, mainly characterised by disproportional short stature, steroid-resistant nephrotic syndrome, spondyloepiphyseal dysplasia, and T-cell immunodeficiency. In the majority of cases, SIOD is caused by pathogenic sequence variants (PSVs) in the SMARCAL1 gene that encodes protein involved in chromatin remodelling. SIOD is an ultra-rare condition, with an incidence of ~1 per 1-3 million live births; data on its genetic and clinical features are scarce. We conducted a retrospective study of 21 paediatric patients with SIOD diagnosed in our centre during the years 2003-2023. The most common extra-renal clinical features were short stature, osseous dysplasia, multiple stigmas, and leukopenia. Proteinuria of varying severity was observed in 16 cases. The five-year overall survival rate (OS) was 89% (95% CI 77-100%), and the ten-year OS was 10%. Next-generation sequencing (NGS) revealed the following PSVs in SMARCAL1 in 19 patients: c.355_500del, c.2542G>T, c.2290C>T, c.2562del, c.2533_2534del, c.1582A>C, c.1933C>T, c.1010T>C, c.1736C>T, c.2070dup, c.2551A>T, c.2149_2150dup, c.939delC, and c.1451T>A; the most common was c.2542G>T, resulting in premature translation termination (p.E848*), and it was found in 14 patients either in a homozygous (four patients) or compound-heterozygous (10 patients) state. According to microsatellite analysis, it is a "founder mutation" in Russia.

Schimke immuno-osseous dysplasia. A case report in Colombia

Background

Schimke immune-osseous dysplasia (SIOD) is an ultra-rare multisystemic, monogenic, and autosomal recessive inherited disease caused by biallelic mutations in the SMARCAL1 gene. Approximately 100 cases have been reported worldwide. The disease is characterized by skeletal, renal, and immunological abnormalities.

Case description

This is a 6-year-old female patient who debuted with nephrotic syndrome at five years of age, with a switch to corticosteroid resistance and poor response to immunosuppressive treatment received. The patient was admitted and referred to our institution due to convulsive status. During her hospitalization, thrombosis was found in the left renal vein, and a renal biopsy report of Collapsing Focal and Segmental Glomerulosclerosis (FSGS) was obtained. The patient had multiple infections during hospitalization, with T lymphocyte lymphopenia and severe IgG hypogammaglobulinemia. Additionally, given dysmorphic facies, delayed weight-height development, and spondyloepiphyseal dysplasia, exome sequencing was performed, finding an homozygous pathogenic variant c.1933C > T p.Arg645Cys in SMARCAL1, compatible with the diagnosis of SIOD.

Discussion

We present the case of a patient that exhibited a severe phenotype of the disease, with skeletal, renal, severe combined immunological compromise and cerebrovascular involvement during follow-up, and the available proposed mechanisms of the disease focused on the clinical manifestations of this patient. It is the first case of SIOD reported in Colombia and the first comprehensive characterization reported in the literature of a patient with homozygosity of the known variant c.1933C > T p.Arg645Cys.

Conclusion

A severe phenotype of the disease with cerebrovascular involvement by homozygosity of the known variant c.1933C > T p.Arg645Cys in the SMARCAL1 gene can be expected.

Successful low-dose immunotherapy after kidney transplantation in a 10-year-old girl with Schimke immuno-osseous dysplasia

BACKGROUND

This case report highlights a successful steroid-free, low-dose immunosuppressive protocol for renal transplantation in a pediatric patient with Schimke immuno-osseous dysplasia with excellent 7-year patient and graft survival. Schimke immuno-osseous dysplasia is a rare multisystem disorder involving the kidney. Renal transplantation is a therapeutic option, but posttransplant mortality is high due to severe infections and posttransplant lymphoproliferative disease.

METHODS

A 10-year-old girl diagnosed with Schimke immuno-osseous dysplasia and end-stage renal disease underwent an AB0-compatible living-related kidney transplantation, with no donor-specific antibodies. Our standard immunosuppression protocol was modified due to the risk of infection. Basiliximab was used as induction therapy, and a reduced dose of mycophenolate mofetil and tacrolimus was initiated following transplantation, maintaining the patient on a low tacrolimus target (3-5 μg/L). Mycophenolate mofetil was discontinued after 8 weeks due to neutropenia and the patient was kept on tacrolimus as monotherapy. Five years posttransplant the patient developed acute onset of neurological symptoms, consisting of ataxia, lack of voluntary coordination, balance, aphasia and dysphagia, and diplopia. She recovered without neurological deficits within 6 weeks. Extensive evaluation revealed no pathology. To avoid a possible a component of tacrolimus-induced cerebral vasoconstriction, the immunosuppressive therapy was changed to everolimus.

RESULTS

Seven years posttransplant, the patient has experienced no serious infections, no rejections, and had excellent graft function, and no de novo donor-specific antibodies.

CONCLUSIONS

The present results indicate that low-dose immunosuppressive therapy after renal transplantation with low immunological risk should be considered for patients with Schimke immuno-osseous dysplasia.

T-cell receptor signaling in Schimke immuno-osseous dysplasia is SMARCAL1-independent

Schimke immuno-osseous dysplasia (SIOD) caused by mutations in SMARCAL1 is an ultra-rare disease characterized by specific facial features, skeletal dysplasia, and steroid-resistant nephrotic syndrome, which often leads to kidney failure and requires transplantation. Cellular (T-cell) deficiency, lymphopenia, and infections have been frequently reported, but whether they are due to T-cell-intrinsic defects in T-cell receptor (TCR) signaling associated with SMARCAL1 deficiency or to T-cell-extrinsic effects such as the impaired proliferation of hematopoietic precursors or T-cell-specific immunosuppression after renal transplantation remains unknown. We have explored the effects of SMARCAL1 deficiency on T-cell receptor signaling in primary and immortalized T cells from a 9-year-old SIOD patient under immunosuppression treatment when compared to healthy donors. Immortalized T cells recapitulated the SMARCAL1 deficiency of the patient, as judged by their impaired response to gamma irradiation. The results indicated that TCR-mediated signaling was normal in SIOD-derived immortalized T cells but strongly impaired in the primary T cells of the patient, although rescued with TCR-independent stimuli such as PMA + ionomycin, suggesting that SIOD-associated T-cell signaling is not intrinsically defective but rather the result of the impaired proliferation of hematopoietic precursors or of T-cell-specific immunosuppression. The lack of early thymic emigrants in our patients may support the former hypothesis.

Sequential Stem Cell-Kidney Transplantation in Schimke Immuno-osseous Dysplasia

Lifelong immunosuppression is required for allograft survival after kidney transplantation but may not ultimately prevent allograft loss resulting from chronic rejection. We developed an approach that attempts to abrogate immune rejection and the need for post-transplantation immunosuppression in three patients with Schimke immuno-osseous dysplasia who had both T-cell immunodeficiency and renal failure. Each patient received sequential transplants of αβ T-cell-depleted and CD19 B-cell-depleted haploidentical hematopoietic stem cells and a kidney from the same donor. Full donor hematopoietic chimerism and functional ex vivo T-cell tolerance was achieved, and the patients continued to have normal renal function without immunosuppression at 22 to 34 months after kidney transplantation. (Funded by the Kruzn for a Kure Foundation.).

Inborn errors of immunity associated with characteristic phenotypes

OBJECTIVES

The aim of the report is to describe the main immunodeficiencies with syndromic characteristics according to the new classification of Inborn Errors of Immunity.

DATA SOURCE

The data search was centered on the PubMed platform on review studies, meta-analyses, systematic reviews, case reports and a randomized study published in the last 10 years that allowed the characterization of the several immunological defects included in this group.

DATA SYNTHESIS

Immunodeficiencies with syndromic characteristics include 65 immunological defects in 9 subgroups. The diversity of clinical manifestations is observed in each described disease and may appear early or later, with variable severity. Congenital thrombocytopenia, syndromes with DNA repair defect, immuno-osseous dysplasias, thymic defects, Hyper IgE Syndrome, anhidrotic ectodermal dysplasia with immunodeficiency and purine nucleoside phosphorylase deficiency were addressed.

CONCLUSIONS

Immunological defects can present with very different characteristics; however, the occurrence of infectious processes, autoimmune disorders and progression to malignancy may suggest diagnostic research. In the case of diseases with gene mutations, family history is of utmost importance.

Podocytic infolding in Schimke immuno-osseous dysplasia with novel SMARCAL1 mutations: a case report

Background

Schimke immuno-osseous dysplasia (SIOD) is a rare autosomal recessive disorder characterized by spondyloepiphyseal dysplasia, progressive renal insufficiency and defective cellular immunity. Podocytic infolding glomerulopathy (PIG) is a newly proposed disease entity characterized by microspheres or microtubular structures associated with podocytes infolding into the glomerular basement membrane (GBM) on electron microscopy (EM).

Case presentation

A 4-year-old boy was admitted to our ward due to proteinuria and edema lasting 1 month. He had a short trunk and demonstrated subtle dysmorphology, with a triangular shape, a broad nasal bridge and a bulbous nasal tip. The laboratory findings were as follows: lymphocytes, 0.5 × 10⁹/L; urine protein, 3.67 g/d; albumin, 9.8 g/L; and cholesterol, 11.72 mmol/L. Skeletal X rays showed small iliac wings, small ossification centers of the capital femoral epiphyses, shallow dysplastic acetabular fossae and mildly flattened vertebrae. The specimen for light microscopy (LM) suggested focal segmental glomerulosclerosis (FSGS). EM revealed a focal thickness of the GBM with some cytoplasmic processes of podocyte infolding into the GBM. Gene sequencing showed novel compound heterozygous mutations in the SMARCAL1 gene (c.2141 + 5G > A; c.2528 + 1G > A) that were inherited from his parents. Finally, we established the diagnosis of SIOD and treated him with diuretics and angiotensin-converting enzyme inhibitors (ACEIs).

Conclusion

The pathogenic mechanism of PIG has not been clarified. Further studies are required to understand whether gene mutations, especially those related to podocytes, contribute to the pathogenesis of podocytic infolding.

Schimke immuno-osseous dysplasia, two new cases with peculiar EEG pattern

Schimke Immuno-Osseous Dysplasia (SIOD) is an autosomal recessive multisystem disorder caused by pathogenic variants in the gene SMARCAL1. The clinical picture is characterized by spondyloepiphyseal dysplasia resulting in growth failure, nephropathy and T-cell deficiency. Neurologic manifestations include microcephaly, cognitive impairment, migraine-like headaches and cerebrovascular manifestations such as cerebral atherosclerotic vascular disease and reversible cerebral vasoconstriction. The role of SMARCAL1 deficiency in non-vascular neurological complications is still under debate. Epilepsy has been reported in a few patients, even in the absence of brain abnormalities. Data regarding electroencephalographic (EEG) patterns in SIOD are scarce METHODS: We describe the clinical, neuroradiological and EEG findings in two unrelated patients with SIOD showing a peculiar pseudo-periodic EEG pattern apparently not related to the cerebrovascular complications, since it was recognized both before and after cerebrovascular events CONCLUSION: Our observations support the hypothesis that SMARCAL1plays an important role in neurodevelopment and brain function and expand the spectrum of neurological abnormalities related to SIOD.

Whole Exome Sequencing Identified a Novel Biallelic SMARCAL1 Mutation in the Extremely Rare Disease SIOD

Schimke immuno-osseous dysplasia (SIOD) is an extremely rare autosomal recessive pleiotropic disease. Although biallelic mutations in SMARCAL1 gene have been reported to be the genetic etiology of SIOD, its molecular diagnosis has been challenging in a relatively proportion of cases due to the extreme rarity. Here, we made a definitive SIOD diagnosis of a 5-year-old girl with an extremely mild phenotype by applying whole exome sequencing (WES). As a result, a novel maternal mutation (c.2141+5G > A) confirmed to create a novel splice donor site combined with a known paternal mutation (c.1933C > T; p.Arg645Cys) were detected. In addition, previous reported SIOD cases showed excessive enrichment for mutations in the helicase ATP-binding and C-terminal domains of SMARCAL1. Similarly, the novel mutation we identified caused a mutant protein truncated in the SMARCAL1 C-terminus. Interestingly, based on the phenotypic profile, compared to reported cases, the patient in our study exhibited milder symptoms with renal dysfunctions limited to asymptomatic proteinuria, but no neurological signs or recurrent infections. Moreover, we identified 73 SMARCAL1-interacting genes, which formed a significant interconnected interaction network with roles in disease-related pathways such as double-strand break repair via homologous recombination, DNA repair, and replication fork processing. Notably, the top 15 SMARCAL1-interacting genes all showed a similar renal temporal expression pattern. Altogether, to our knowledge, the case in this study is the first case diagnosed originally based on a genetic test via WES rather than a characteristic phenotype. The identification of the novel allelic mutation (c.2141+5G > A) extends the phenotypic spectrum of SMARCAL1 mutations and the following bioinformatics analysis presents additional genetic evidence to illustrate the role of SMARCAL1 in SIOD.

Schimke immunoosseous dysplasia and management considerations for vascular risks

Schimke immunoosseous dysplasia (SIOD) is a multisystemic condition characterized by early arteriosclerosis and progressive renal insufficiency, among other features. Many SIOD patients have severe, migraine-like headaches, transient neurologic attacks, or cerebral ischemic events. Cerebral events could be exacerbated or precipitated by hypertension, and it is unclear how these are related to arteriosclerotic changes as dyslipidemia is also a feature of SIOD. The correlation between hypercholesterolemia and cardiovascular risk in SIOD is unclear. Also, the etiology and management of headaches is not well characterized. Here we report our clinical observations in the management of SIOD in a patient who was diagnosed in school age despite early signs and symptoms. We describe biallelic variants, including a previously unreported c.1931G>A (p.Arg644Gln) variant in SMARCAL1. We specifically investigated whether migraine-like headaches and progressive nephropathy may be related to blood pressure dysregulation. We found a correlation between tighter blood pressure regulation using ambulatory blood pressure monitoring and a subjective decrease in headache symptoms. We discuss blood pressure medication management in SIOD. We also characterize dyslipidemia relative to atherosclerosis risks and provide new management strategies to consider for optimizing care.

Low renal but high extrarenal phenotype variability in Schimke immuno-osseous dysplasia

Schimke immuno-osseous dysplasia (SIOD) is a rare multisystem disorder with early mortality and steroid-resistant nephrotic syndrome (SRNS) progressing to end-stage kidney disease. We hypothesized that next-generation gene panel sequencing may unsurface oligosymptomatic cases of SIOD with potentially milder disease courses. We analyzed the renal and extrarenal phenotypic spectrum and genotype-phenotype associations in 34 patients from 28 families, the largest SMARCAL1-associated nephropathy cohort to date. In 11 patients the diagnosis was made unsuspectedly through SRNS gene panel testing. Renal disease first manifested at median age 4.5 yrs, with focal segmental glmerulosclerosis or minimal change nephropathy on biopsy and rapid progression to end-stage kidney disease (ESKD) at median age 8.7 yrs. Whereas patients diagnosed by phenotype more frequently developed severe extrarenal complications (cerebral ischemic events, septicemia) and were more likely to die before age 10 years than patients identified by SRNS-gene panel screening (88 vs. 40%), the subgroups did not differ with respect to age at proteinuria onset and progression to ESKD. Also, 10 of 11 children diagnosed unsuspectedly by Next Generation Sequencing were small at diagnosis and all showed progressive growth failure. Severe phenotypes were usually associated with biallelic truncating mutations and milder phenotypes with biallelic missense mutations. However, no genotype-phenotype correlation was observed for the renal disease course. In conclusion, while short stature is a reliable clue to SIOD in children with SRNS, other systemic features are highly variable. Our findings support routine SMARCAL1 testing also in non-syndromic SRNS.

Increased Wnt and Notch signaling: a clue to the renal disease in Schimke immuno-osseous dysplasia?

Background

Schimke immuno-osseous dysplasia (SIOD) is a multisystemic disorder caused by biallelic mutations in the SWI/SNF-related matrix-associated actin-dependent regulator of chromatin, subfamily A-like 1 (SMARCAL1) gene. Changes in gene expression underlie the arteriosclerosis and T-cell immunodeficiency of SIOD; therefore, we hypothesized that SMARCAL1 deficiency causes the focal segmental glomerulosclerosis (FSGS) of SIOD by altering renal gene expression. We tested this hypothesis by gene expression analysis of an SIOD patient kidney and verified these findings through immunofluorescent analysis in additional SIOD patients and a genetic interaction analysis in Drosophila.

Results

We found increased expression of components and targets of the Wnt and Notch signaling pathways in the SIOD patient kidney, increased levels of unphosphorylated β-catenin and Notch1 intracellular domain in the glomeruli of most SIOD patient kidneys, and genetic interaction between the Drosophila SMARCAL1 homologue Marcal1 and genes of the Wnt and Notch signaling pathways.

Conclusions

We conclude that increased Wnt and Notch activity result from SMARCAL1 deficiency and, as established causes of FSGS, contribute to the renal disease of most SIOD patients. This further clarifies the pathogenesis of SIOD and will hopefully direct potential therapeutic approaches for SIOD patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-016-0519-7) contains supplementary material, which is available to authorized users.

The Genetics of Nephrotic Syndrome

Nephrotic syndrome (NS) is a common pediatric kidney disease and is defined as massive proteinuria, hypoalbuminemia, and edema. Dysfunction of the glomerular filtration barrier, which is made up of endothelial cells, glomerular basement membrane, and visceral epithelial cells known as podocytes, is evident in children with NS. While most children have steroid-responsive nephrotic syndrome (SSNS), approximately 20% have steroid-resistant nephrotic syndrome (SRNS) and are at risk for progressive kidney dysfunction. While the cause of SSNS is still not well understood, there has been an explosion of research into the genetic causes of SRNS in the past 15 years. More than 30 proteins regulating the function of the glomerular filtration barrier have been associated with SRNS including podocyte slit diaphragm proteins, podocyte actin cytoskeletal proteins, mitochondrial proteins, adhesion and glomerular basement membrane proteins, transcription factors, and others. A genetic cause of SRNS can be found in approximately 70% of infants presenting in the first 3 months of life and 50% of infants presenting between 4 and 12 months, with much lower likelihood for older patients. Identification of the underlying genetic etiology of SRNS is important in children because it allows for counseling of other family members who may be at risk, predicts risk of recurrent disease after kidney transplant, and predicts response to immunosuppressive therapy. Correlations between genetic mutation and clinical phenotype as well as genetic risk factors for SSNS and SRNS are reviewed in this article.