Recessive missense mutations in LAMB2 expand the clinical spectrum of LAMB2-associated disorders

The clinical characteristics and genotype analysis of LAMB2 gene mutation

Purpose

To report a case of steroid-resistant nephrotic syndrome caused by a LAMB2 gene mutation, examine the associated literature, outline the clinical and genetic features of Pierson syndrome, and deepen the clinical comprehension of this condition.

Method

The study involved retrospective summary and analysis of the clinical presentations, genetic mutation features, and prognosis of one case involving a LAMB2 gene mutation. PubMed, Medline, Web of Science, CNKI, and Wanfang databases were searched to gather and summarize information on the pathological phenotypes and genotypic alterations associated with LAMB2 mutations.

Result

A 9-month-old infant presented with edema and massive proteinuria, along with horizontal nystagmus and miosis, manifesting clinically as steroid-resistant nephrotic syndrome. Ocular symptoms prompted both a kidney biopsy and genetic testing. The biopsy revealed minimal change disease, while genetic testing identified compound heterozygous mutations in the LAMB2 gene: c.1405C > T (p.R469X) and c.1066 T > A (p.C356S), inherited from the father and mother, respectively. These mutations were determined to be novel. The diagnosis was confirmed as a LAMB2 gene mutation. A literature review of 26 cases with LAMB2 mutations indicated these typically presented as steroid-resistant or congenital nephrotic syndrome, with 14 cases also displaying ocular symptoms. Among the 18 cases undergoing kidney biopsy, findings included focal segmental glomerulosclerosis in 10 cases, minimal change disease in 4 cases, diffuse mesangial sclerosis in 2 cases, IgM nephropathy in 1 case, and mesangial proliferation in 1 case. Electron microscopy in 10 cases showed basement membrane splitting. Genetic analysis revealed 15 cases with compound heterozygous mutations, 5 with homozygous mutations, 3 with heterozygous mutations, 2 with frame-shift mutations, and 1 with a truncating mutation. 16 out of the 26 reported cases progressed to end-stage kidney disease.

Conclusion

Mutations in the LAMB2 gene primarily manifest as steroid-resistant or congenital nephrotic syndrome, often accompanied by ocular abnormalities, suggesting a strong likelihood of this disease. The results of genetic testing offer a foundational basis for clinical diagnosis. The identification of a new mutation site in this case expands the known spectrum of mutations in the LAMB2 gene. Unfortunately, the prognosis associated with this condition is generally poor.

Nephrotic Syndrome Throughout Childhood: Diagnosing Podocytopathies From the Womb to the Dorm

The etiologies of podocyte dysfunction that lead to pediatric nephrotic syndrome (NS) are vast and vary with age at presentation. The discovery of numerous novel genetic podocytopathies and the evolution of diagnostic technologies has transformed the investigation of steroid-resistant NS while simultaneously promoting the replacement of traditional morphology-based disease classifications with a mechanistic approach. Podocytopathies associated with primary and secondary steroid-resistant NS manifest as diffuse mesangial sclerosis, minimal change disease, focal segmental glomerulosclerosis, and collapsing glomerulopathy. Molecular testing, once an ancillary option, has become a vital component of the clinical investigation and when paired with kidney biopsy findings, provides data that can optimize treatment and prognosis. This review focuses on the causes including selected monogenic defects, clinical phenotypes, histopathologic findings, and age-appropriate differential diagnoses of nephrotic syndrome in the pediatric population with an emphasis on podocytopathies.

Congenital anterior segment ocular disorders: Genotype-phenotype correlations and emerging novel mechanisms

Development of the anterior segment of the eye requires reciprocal sequential interactions between the arising tissues, facilitated by numerous genetic factors. Disruption of any of these processes results in congenital anomalies in the affected tissue(s) leading to anterior segment disorders (ASD) including aniridia, Axenfeld-Rieger anomaly, congenital corneal opacities (Peters anomaly, cornea plana, congenital primary aphakia), and primary congenital glaucoma. Current understanding of the genetic factors involved in ASD remains incomplete, with approximately 50% overall receiving a genetic diagnosis. While some genes are strongly associated with a specific clinical diagnosis, the majority of known factors are linked with highly variable phenotypic presentations, with pathogenic variants in FOXC1, CYP1B1, and PITX2 associated with the broadest spectrum of ASD conditions. This review discusses typical clinical presentations including associated systemic features of various forms of ASD; the latest functional data and genotype-phenotype correlations related to 25 ASD factors including newly identified genes; promising novel candidates; and current and emerging treatments for these complex conditions. Recent developments of interest in the genetics of ASD include identification of phenotypic expansions for several factors, discovery of multiple modes of inheritance for some genes, and novel mechanisms including a growing number of non-coding variants and alleles affecting specific domains/residues and requiring further studies.

LAMB2 gene: broad clinical spectrum in Pierson syndrome

Pierson syndrome (PS) is a rare autosomal recessive disease, characterized by congenital nephrotic syndrome (CNS), and ocular and neurologic abnormalities. In affected cases, there is abnormal b-2 laminin which is compound of the several basement membranes caused by inherited mutations in the LAMB2 gene. Although patients have mutations in the same gene, the phenotype is highly variable. In this case series, the relationship between genotype and phenotype is emphasized, and information about the clinical follow-up of the patients is presented. Hereby, we report four pediatric cases with PS as a result of mutation in the LAMB2 gene. Clinical spectrum of LAMB2-associated disorders varies from mild-to-severe ocular, kidney, and neurologic involvement. Since genotype-phenotype correlation in PS has not been clearly demonstrated, we recommend that all patients with ophthalmic anomalies and glomerular proteinuria should be tested for LAMB2 mutations.

Calcium signaling crosstalk between the endoplasmic reticulum and mitochondria, a new drug development strategies of kidney diseases

Calcium (Ca2+) acts as a second messenger and constitutes a complex and large information exchange system between the endoplasmic reticulum (ER) and mitochondria; this process is involved in various life activities, such as energy metabolism, cell proliferation and apoptosis. Increasing evidence has suggested that alterations in Ca2+ crosstalk between the ER and mitochondria, including alterations in ER and mitochondrial Ca2+ channels and related Ca2+ regulatory proteins, such as sarco/endoplasmic reticulum Ca2+-ATPase (SERCA), inositol 1,4,5-trisphosphate receptor (IP3R), and calnexin (CNX), are closely associated with the development of kidney disease. Therapies targeting intracellular Ca2+ signaling have emerged as an emerging field in the treatment of renal diseases. In this review, we focused on recent advances in Ca2+ signaling, ER and mitochondrial Ca2+ monitoring methods and Ca2+ homeostasis in the development of renal diseases and sought to identify new targets and insights for the treatment of renal diseases by targeting Ca2+ channels or related Ca2+ regulatory proteins.

Tips for Testing Adults With Suspected Genetic Kidney Disease

Genetic kidney disease is common but often unrecognized. It accounts for most cystic kidney diseases and tubulopathies, many forms of congenital abnormalities of the kidney and urinary tract (CAKUT), and some glomerulopathies. Genetic kidney disease is typically suspected where the disease usually has a genetic basis or there is another affected family member, a young age at onset, or extrarenal involvement, but there are also many exceptions to these "rules". Genetic testing requires the patient's written informed consent. When a patient declines testing, another later conversation may be worthwhile. Genetic testing not only indicates the diagnosis but also the inheritance pattern, likely at-risk family members, disease in other organs, clinical course, and possibly effective treatments. Sometimes genetic testing does not identify a pathogenic variant even where other evidence is strong. A variant of uncertain significance (VUS) may be reported but should not be used for clinical decision making. It may be reclassified after more information becomes available without necessarily retesting the patient. Patients should be provided with a copy of their genetic test report, the results explained, and at-risk family members offered "cascade" testing. A referral to a clinical geneticist or genetic counselor helps identify affected family members and in providing advice to assist with reproductive decisions.

Phenotype, genotype, and clinical outcome of Taiwanese with congenital nephrotic syndrome

BACKGROUND/PURPOSE

Congenital nephrotic syndrome (CNS) is one of the important causes of end-stage kidney disease in children. Studies on the genotype, phenotype, and clinical outcome in infants with CNS caused by genetic mutations are scarce.

METHODS

We analyzed the genetic background, clinical manifestations, treatment response, and prognosis of pediatric patients with CNS in Taiwan.

RESULTS

Fifteen infants with CNS were enrolled, and 11 patients of median age 21 (interquartile range 3∼44) days caused by genetic mutations from 10 unrelated families were included in the study. Of the eleven patients, 9 had extra-renal manifestations including microcephaly, facial dysmorphism, and skeletal anomalies. More than two-thirds of the patients had disease onset before 1 month of age. Diffuse meningeal sclerosis was the most common histological characteristic. Whole exome sequencing followed by direct Sanger sequence revealed mutations in OSGEP (R247Q), WT1 (R366H and R467Q), LAMB2 (Q1209∗ and c. 5432-5451 19 bp deletion), NUP93 (D302V), and LAGE3 (c.188+1G > A). Three of the variants were novel. Corticosteroids and/or immunosuppressants were administered in 2 patients, but both were refractory to treatment. During the mean 3.5 years of follow-up, all but two died of uremia and sepsis. The two survivors reached end-stage kidney disease and required peritoneal dialysis, and one of them underwent uneventful renal transplantation.

CONCLUSION

The majority of patients with CNS in Taiwan were caused by OSGEP followed by WT1 mutation. R247Q is the hotspot mutation of OSGEP in Taiwan. CNS patients in Taiwan suffer from significant morbidity and mortality.

Ocular manifestations of the genetic causes of focal and segmental glomerulosclerosis

Genetic forms of focal and segmental glomerulosclerosis (FSGS) often have extra-renal manifestations. This study examined FSGS-associated genes from the Genomics England Renal proteinuria panel for reported and likely ocular features. Thirty-two of the 55 genes (58%) were associated with ocular abnormalities in human disease, and a further 12 (22%) were expressed in the retina or had an eye phenotype in mouse models. The commonest genes affected in congenital nephrotic syndrome (NPHS1, NPHS2, WT1, LAMB2, PAX2 but not PLCE1) may have ocular manifestations . Many genes affected in childhood-adolescent onset FSGS (NPHS1, NPHS2, WT1, LAMB2, SMARCAL1, NUP107 but not TRPC6 or PLCE1) have ocular features. The commonest genes affected in adult-onset FSGS (COL4A3-COL4A5, GLA ) have ocular abnormalities but not the other frequently affected genes (ACTN4, CD2AP, INF2, TRPC6). Common ocular associations of genetic FSGS include cataract, myopia, strabismus, ptosis and retinal atrophy. Mitochondrial forms of FSGS (MELAS, MIDD, Kearn's Sayre disease) are associated with retinal atrophy and inherited retinal degeneration. Some genetic kidney diseases (CAKUT, ciliopathies, tubulopathies) that result in secondary forms of FSGS also have ocular features. Ocular manifestations suggest a genetic basis for FSGS, often help identify the affected gene, and prompt genetic testing. In general, ocular abnormalities require early evaluation by an ophthalmologist, and sometimes, monitoring or treatment to improve vision or prevent visual loss from complications. In addition, the patient should be examined for other syndromic features and first degree family members assessed.

Early-Onset Myopia and Retinal Detachment without Typical Microcoria or Severe Proteinuria due to a Novel LAMB2 Variant

PURPOSE

To describe the ocular and renal features, as well as outcomes of retinal detachment repair, in patients with a novel, homozygous laminin β-2 (LAMB2) pathogenic variant.

DESIGN

Single-center retrospective chart review of patients with a homozygous variant, c.619T>C p.(Ser207Pro), in the LAMB2 gene.

SUBJECTS

Eleven patients (22 eyes) from 4 families.

METHODS

Demographic data and ocular findings were recorded. Patients were recalled for a detailed renal evaluation.

MAIN OUTCOME MEASURES

Ocular features, renal features, and outcomes of retinal detachment repair.

RESULTS

The mean age at presentation was 6.0 (range, 1-26) years. None of the study eyes had microcoria, and none of the patients had nephrotic-range proteinuria. The mean refraction and axial length were -7.9 diopters (range, -4.0 to -12.0 diopters) and 25.3 (range, 22.7-27.7) mm, respectively. Eleven eyes (50%) had cataract at presentation. Fifteen eyes had a clear view to the fundus and all showed tessellated myopic fundus, avascular peripheral retina evident clinically or on fluorescein angiography, and rudimentary fovea. Optic disc pallor was observed in 10 eyes (66.7%). Straightened retinal vessels, abnormal vascular emanation (situs inversus) from the optic disc, supernumerary vascular branching at the optic disc, and vascular tortuosity were observed in 10 (66.7%), 2 (13.4%), 2 (13.4%), and 2 (13.4%) eyes, respectively. Discrete areas of punched-out chorioretinal atrophy were observed in 4 (26.7%) eyes. Spectral-domain OCT showed retinal and choroidal thinning in 13 eyes (86.7%), retinoschisis temporal to the fovea in 2 eyes (13.4%), and rudimentary fovea in 15 eyes (100%). Among the 22 eyes, 14 eyes (63.6%) developed rhegmatogenous retinal detachment (RRD), mostly during childhood, of which 5 patients had bilateral RRD. Eight eyes were operated on and 6 (75%) achieved retinal reattachment at the last follow-up. The mean preoperative visual acuity was 20/300 and the mean postoperative visual acuity at the last follow-up was 20/400.

CONCLUSIONS

This study describes a distinct phenotype of LAMB2-related disease with a novel, homozygous LAMB2 variant, and further expands the spectrum of ophthalmic and renal features, and the molecular genetic basis, of LAMB2-related disease. Because the typical microcoria and nephrotic-range proteinuria might be absent, the retinal features can guide the diagnosis.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any materials discussed in this article.

Artificial intelligence and the analysis of cryo-EM data provide structural insight into the molecular mechanisms underlying LN-lamininopathies

Laminins (Lm) are major components of basement membranes (BM), which polymerize to form a planar lattice on cell surface. Genetic alternations of Lm affect their oligomerization patterns and lead to failures in BM assembly manifesting in a group of human disorders collectively defined as Lm N-terminal domain lamininopathies (LN-lamininopathies). We have employed a recently determined cryo-EM structure of the Lm polymer node, the basic repeating unit of the Lm lattice, along with structure prediction and modeling to systematically analyze structures of twenty-three pathogenic Lm polymer nodes implicated in human disease. Our analysis provides the detailed mechanistic explanation how Lm mutations lead to failures in Lm polymerization underlining LN-lamininopathies. We propose the new categorization scheme of LN-lamininopathies based on the insight gained from the structural analysis. Our results can help to facilitate rational drug design aiming in the treatment of Lm deficiencies.

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.

Systematic Review of Clinical Characteristics and Genotype-Phenotype Correlation in LAMB2-Associated Disease

Introduction

Laminin subunit beta-2 (LAMB2)-associated disease, termed Pierson syndrome, presents with congenital nephrotic syndrome, ocular symptoms, and neuromuscular symptoms. In recent years, however, the widespread use of next-generation sequencing (NGS) has helped to discover a variety of phenotypes associated with this disease. Therefore, we conducted this systematic review.

Methods

A literature search of patients with LAMB2 variants was conducted, and 110 patients were investigated, including 12 of our patients. For genotype-phenotype correlation analyses, the extracted data were investigated for pathogenic variant types, the severity of nephropathy, and extrarenal symptoms. Survival analyses were also performed for the onset age of end-stage kidney disease (ESKD).

Results

Among all patients, 81 (78%) presented with congenital nephrotic syndrome, and 52 (55%) developed ESKD within 12 months. The median age at ESKD onset was 6.0 months. Kidney survival analysis showed that patients with biallelic truncating variants had a significantly earlier progression to ESKD than those with other variants (median age 1.2 months vs. 60.0 months, P < 0.05). Although the laminin N-terminal domain is functionally important in laminin proteins, and variants in the laminin N-terminal domain are said to result in a severe kidney phenotype such as earlier onset age and worse prognosis, there were no significant differences in onset age of nephropathy and progression to ESKD between patients with nontruncating variants located in the laminin N-terminal domain and those with variants located outside this domain.

Conclusion

This study revealed a diversity of LAMB2-associated diseases, characteristics of LAMB2 nephropathy, and genotype-phenotype correlations.

Case of Pierson syndrome presented with hyphema,vitrous haemorrhage and subsequent neovascular glaucoma

BACKGROUND

Pierson syndrome is a rare autosomal recessive disorder that causes congenital nephrotic syndrome, neurodevelopmental abnormalities, and several ocular signs. The Pierson syndrome is caused by a mutation of the LAMB2 gene, that encodes laminin beta 2, which is expressed in the glomerular basement membrane, in neuromuscular junctions, and within ocular structures. First described by Pierson et al., the ocular signs of Pierson syndrome include microcoria, which is most characteristic sign, as well as iris abnormalities, cataract, glaucoma, and retinal detachment.

CASE PRESENTATION

Herein, we report the case of a young female who, at 16 months, was diagnosed with congenital nephrotic syndrome, subsequently underwent a kidney transplant at age 4,did cataract surgery with IOL implantation in both eyes at age of 2 years and presented with ocular signs including high myopia, band keratopathy, t, nystagmus, retina, and optic nerve atrophy, she did not show nor did the family report any neurodevelopmental abnormalities. her genetic studies this missense variant c.970T< C p. (Cys324Arg) of LAMB2, later she developed spontaneous hyphema along with vitreous haemorrhage and increased intra ocular pressure in her left eye, she underwent cyclophotocouagulation to treat her high IOP.

CONCLUSION

LAMB 2 mutations can be associated with multiple ocular signs that varies from mild to severe form, we are her to report our case who did not present with the typical ocular sign of microcoria for PS, did not have any neurodevelopmental  abnormality and presented with hyphaemia 2ndry to iris neovascularisation with vitreous haemorrhage with neovascular glaucoma.

Clinical and Pathologic Features of Congenital Myasthenic Syndromes Caused by 35 Genes-A Comprehensive Review

Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders characterized by impaired neuromuscular signal transmission due to germline pathogenic variants in genes expressed at the neuromuscular junction (NMJ). A total of 35 genes have been reported in CMS (AGRN, ALG14, ALG2, CHAT, CHD8, CHRNA1, CHRNB1, CHRND, CHRNE, CHRNG, COL13A1, COLQ, DOK7, DPAGT1, GFPT1, GMPPB, LAMA5, LAMB2, LRP4, MUSK, MYO9A, PLEC, PREPL, PURA, RAPSN, RPH3A, SCN4A, SLC18A3, SLC25A1, SLC5A7, SNAP25, SYT2, TOR1AIP1, UNC13A, VAMP1). The 35 genes can be classified into 14 groups according to the pathomechanical, clinical, and therapeutic features of CMS patients. Measurement of compound muscle action potentials elicited by repetitive nerve stimulation is required to diagnose CMS. Clinical and electrophysiological features are not sufficient to identify a defective molecule, and genetic studies are always required for accurate diagnosis. From a pharmacological point of view, cholinesterase inhibitors are effective in most groups of CMS, but are contraindicated in some groups of CMS. Similarly, ephedrine, salbutamol (albuterol), amifampridine are effective in most but not all groups of CMS. This review extensively covers pathomechanical and clinical features of CMS by citing 442 relevant articles.

Monogenic focal segmental glomerulosclerosis: A conceptual framework for identification and management of a heterogeneous disease

Focal segmental glomerulosclerosis (FSGS) is not a disease, rather a pattern of histological injury occurring from a variety of causes. The exact pathogenesis has yet to be fully elucidated but is likely varied based on the type of injury and the primary target of that injury. However, the approach to treatment is often based on the degree of podocyte foot process effacement and clinical presentation without sufficient attention paid to etiology. In this regard, there are many monogenic causes of FSGS with variable presentation from nephrotic syndrome with histological features of primary podocytopathy to more modest degrees of proteinuria with limited evidence of podocyte foot process injury. It is likely that genetic causes are largely underdiagnosed, as the role and the timing of genetic testing in FSGS is not established and genetic counseling, testing options, and interpretation of genotype in the context of phenotype may be outside the scope of practice for both nephrologists and geneticists. Yet most clinicians believe that a genetic diagnosis can lead to targeted therapy, limit the use of high-dose corticosteroids as a therapeutic trial, and allow the prediction of the natural history and risk for recurrence in the transplanted kidney. In this manuscript, we emphasize that genetic FSGS is not monolithic in its presentation, opine on the importance of genetic testing and provide an algorithmic approach to deployment of genetic testing in a timely fashion when faced with a patient with FSGS.

Biochemical composition of the glomerular extracellular matrix in patients with diabetic kidney disease

In the glomeruli, mesangial cells produce mesangial matrix while podocytes wrap glomerular capillaries with cellular extensions named foot processes and tether the glomerular basement membrane (GBM). The turnover of the mature GBM and the ability of adult podocytes to repair injured GBM are unclear. The actin cytoskeleton is a major cytoplasmic component of podocyte foot processes and links the cell to the GBM. Predominant components of the normal glomerular extracellular matrix (ECM) include glycosaminoglycans, proteoglycans, laminins, fibronectin-1, and several types of collagen. In patients with diabetes, multiorgan composition of extracellular tissues is anomalous, including the kidney, so that the constitution and arrangement of glomerular ECM is profoundly altered. In patients with diabetic kidney disease (DKD), the global quantity of glomerular ECM is increased. The level of sulfated proteoglycans is reduced while hyaluronic acid is augmented, compared to control subjects. The concentration of mesangial fibronectin-1 varies depending on the stage of DKD. Mesangial type III collagen is abundant in patients with DKD, unlike normal kidneys. The amount of type V and type VI collagens is higher in DKD and increases with the progression of the disease. The GBM contains lower amount of type IV collagen in DKD compared to normal tissue. Further, genetic variants in the α3 chain of type IV collagen may modulate susceptibility to DKD and end-stage kidney disease. Human cellular models of glomerular cells, analyses of human glomerular proteome, and improved microscopy procedures have been developed to investigate the molecular composition and organization of the human glomerular ECM.

A novel model of nephrotic syndrome results from a point mutation in Lama5 and is modified by genetic background

Nephrotic syndrome is characterized by severe proteinuria, hypoalbuminaemia, edema and hyperlipidaemia. Genetic studies of nephrotic syndrome have led to the identification of proteins playing a crucial role in slit diaphragm signaling, regulation of actin cytoskeleton dynamics and cell-matrix interactions. The laminin α5 chain is essential for embryonic development and, in association with laminin β2 and laminin γ1, is a major component of the glomerular basement membrane, a critical component of the glomerular filtration barrier. Mutations in LAMA5 were recently identified in children with nephrotic syndrome. Here, we have identified a novel missense mutation (E884G) in the uncharacterized L4a domain of LAMA5 where homozygous mice develop nephrotic syndrome with severe proteinuria with histological and ultrastructural changes in the glomerulus mimicking the progression seen in most patients. The levels of LAMA5 are reduced in vivo and the assembly of the laminin 521 heterotrimer significantly reduced in vitro. Proteomic analysis of the glomerular extracellular fraction revealed changes in the matrix composition. Importantly, the genetic background of the mice had a significant effect on aspects of disease progression from proteinuria to changes in podocyte morphology. Thus, our novel model will provide insights into pathologic mechanisms of nephrotic syndrome and pathways that influence the response to a dysfunctional glomerular basement membrane that may be important in a range of kidney diseases.

Management of Steroid-Resistant Nephrotic Syndrome in Children

Nephrotic syndrome (NS) affects 115-169 children per 100,000, with rates varying by ethnicity and location. Immune dysregulation, systemic circulating substances, or hereditary structural abnormalities of the podocyte are considered to have a role in the etiology of idiopathic NS. Following daily therapy with corticosteroids, more than 85% of children and adolescents (often aged 1 to 12 years) with idiopathic nephrotic syndrome have full proteinuria remission. Patients with steroid-resistant nephrotic syndrome (SRNS) do not demonstrate remission after four weeks of daily prednisolone therapy. The incidence of steroid-resistant nephrotic syndrome in children varies between 35 and 92 percent. A third of SRNS patients have mutations in one of the important podocyte genes. An unidentified circulating factor is most likely to blame for the remaining instances of SRNS.

The aim of this article is to explore and review the genetic factors and management of steroid-resistant nephrotic syndrome. An all language literature search was conducted on MEDLINE, COCHRANE, EMBASE, and Google Scholar till September 2021. The following search strings and Medical Subject Headings (MeSH) terms were used: “Steroid resistance”, “nephrotic syndrome”, “nephrosis” and “hypoalbuminemia”. We comprehensively reviewed the literature on the epidemiology, genetics, current treatment protocols, and management of steroid-resistant nephrotic syndrome.

We found that for individuals with non-genetic SRNS, calcineurin inhibitors (cyclosporine and tacrolimus) constitute the current mainstay of treatment, with around 70% of patients achieving full or partial remission and an acceptable long-term prognosis. Patients with SRNS who do not react to calcineurin inhibitors or other immunosuppressive medications may have deterioration in kidney function and may develop end-stage renal failure. Nonspecific renal protective medicines, such as angiotensin-converting enzyme inhibitors, angiotensin 2 receptor blockers, and anti-lipid medications, slow the course of the illness. Recurrent focal segmental glomerulosclerosis in the allograft affects around a third of individuals who get a kidney transplant, and it frequently responds to a combination of plasma exchange, rituximab, and increased immunosuppression. Despite the fact that these results show a considerable improvement in outcome, further multicenter controlled studies are required to determine the optimum drugs and regimens to be used.

Congenital nephrotic syndrome

Congenital nephrotic syndrome (CNS), a challenging form of nephrotic syndrome, is characterized by massive proteinuria, hypoalbuminemia, and edema. Extensive leakage of plasma proteins is the main feature of CNS. Patients can be diagnosed in utero or during the first few weeks of life, usually before three months. The etiology of CNS can be related to either genetic or nongenetic etiologies. Pathogenic variants in NPHS1, NPHS2, LAMB2, WT1, and PLCE1 genes have been implicated in this disease. The clinical course is complicated by significant edema, infections, thrombosis, hypothyroidism, failure to thrive, and others. Obtaining vascular access, frequent intravenous albumin infusions, diuretic use, infection prevention, and nutritional support are the mainstay management during their first month of life. The best therapy for these patients is kidney transplantation. CNS diagnosis and treatment continue to be a challenge for clinicians. This review increases the awareness about the pathogenesis, diagnosis, and management of CNS patients.

Glomerular Endothelial Cell-Derived microRNA-192 Regulates Nephronectin Expression in Idiopathic Membranous Glomerulonephritis

BACKGROUND

Autoantibodies binding to podocyte antigens cause idiopathic membranous glomerulonephritis (iMGN). However, it remains elusive how autoantibodies reach the subepithelial space because the glomerular filtration barrier (GFB) is size selective and almost impermeable for antibodies.

METHODS

Kidney biopsies from patients with iMGN, cell culture, zebrafish, and mouse models were used to investigate the role of nephronectin (NPNT) regulating microRNAs (miRs) for the GFB.

RESULTS

Glomerular endothelial cell (GEC)-derived miR-192-5p and podocyte-derived miR-378a-3p are upregulated in urine and glomeruli of patients with iMGN, whereas glomerular NPNT is reduced. Overexpression of miR-192-5p and morpholino-mediated npnt knockdown induced edema, proteinuria, and podocyte effacement similar to podocyte-derived miR-378a-3p in zebrafish. Structural changes of the glomerular basement membrane (GBM) with increased lucidity, splitting, and lamellation, especially of the lamina rara interna, similar to ultrastructural findings seen in advanced stages of iMGN, were found. IgG-size nanoparticles accumulated in lucidity areas of the lamina rara interna and lamina densa of the GBM in npnt-knockdown zebrafish models. Loss of slit diaphragm proteins and severe structural impairment of the GBM were further confirmed in podocyte-specific Npnt knockout mice. GECs downregulate podocyte NPNT by transfer of miR-192-5p-containing exosomes in a paracrine manner.

CONCLUSIONS

Podocyte NPNT is important for proper glomerular filter function and GBM structure and is regulated by GEC-derived miR-192-5p and podocyte-derived miR-378a-3p. We hypothesize that loss of NPNT in the GBM is an important part of the initial pathophysiology of iMGN and enables autoantigenicity of podocyte antigens and subepithelial immune complex deposition in iMGN.

Laminin Polymerization and Inherited Disease: Lessons From Genetics

The laminins (LM) are a family of basement membranes glycoproteins with essential structural roles in supporting epithelia, endothelia, nerves and muscle adhesion, and signaling roles in regulating cell migration, proliferation, stem cell maintenance and differentiation. Laminins are obligate heterotrimers comprised of α, β and γ chains that assemble intracellularly. However, extracellularly these heterotrimers then assemble into higher-order networks via interaction between their laminin N-terminal (LN) domains. In vitro protein studies have identified assembly kinetics and the structural motifs involved in binding of adjacent LN domains. The physiological importance of these interactions has been identified through the study of pathogenic point mutations in LN domains that lead to syndromic disorders presenting with phenotypes dependent on which laminin gene is mutated. Genotype-phenotype comparison between knockout and LN domain missense mutations of the same laminin allows inferences to be drawn about the roles of laminin network assembly in terms of tissue function. In this review, we will discuss these comparisons in terms of laminin disorders, and the therapeutic options that understanding these processes have allowed. We will also discuss recent findings of non-laminin mediators of laminin network assembly and their implications in terms of basement membrane structure and function.

Five-Year Follow-Up and Successful Kidney Transplantation in a Girl with a Severe Phenotype of Pierson Syndrome

Pierson syndrome (PIERSS) is a rare autosomal recessive disorder characterized by the combination of congenital nephrotic syndrome (CNS) and extrarenal symptoms including ocular malformations and neurodevelopmental deficits. PIERSS is caused by biallelic pathogenic variants in the LAMB2 gene leading to the defects of β2-laminin, the protein mainly expressed in the glomerular basement membrane, ocular structures, and neuromuscular junctions. Severe complications of PIERSS lead to the fatal outcome in early childhood in majority of the cases. We report a case of 5-year-old girl with severe phenotype of PIERSS caused by biallelic functional null variants of the LAMB2 gene. Due to consequences of CNS, the patient required bilateral nephrectomy and peritoneal dialysis since early infancy. The course was additionally complicated by tubulopathy, life-threatening infections, severe hypertension, erythropoietin-resistant anemia, generalized muscular hypotonia, neurogenic bladder, profound neurodevelopmental delay, epilepsy, gastrointestinal problems, secondary hypothyroidism, and necessity of repeated ocular surgery due to microcoria, cataract, and nystagmus. Due to multidisciplinary efforts, at the age of 4 years, the kidney transplantation was possible. Currently, the renal graft has an excellent function; however, the girl presents severe neurodevelopmental delay. The report presents a unique long-term follow-up of severe PIERSS with a few new phenotypical findings. It highlights the clinical problems and challenges in management of this rare condition.

Laminin β2 variants associated with isolated nephropathy that impact matrix regulation

Mutations in LAMB2, encoding laminin β₂, cause Pierson syndrome and occasionally milder nephropathy without extrarenal abnormalities. The most deleterious missense mutations that have been identified affect primarily the N-terminus of laminin β₂. On the other hand, those associated with isolated nephropathy are distributed across the entire molecule, and variants in the β₂ LEa-LF-LEb domains are exclusively found in cases with isolated nephropathy. Here we report the clinical features of mild isolated nephropathy associated with 3 LAMB2 variants in the LEa-LF-LEb domains (p.R469Q, p.G699R, and p.R1078C) and their biochemical characterization. Although Pierson syndrome missense mutations often inhibit laminin β₂ secretion, the 3 recombinant variants were secreted as efficiently as WT. However, the β₂ variants lost pH dependency for heparin binding, resulting in aberrant binding under physiologic conditions. This suggests that the binding of laminin β₂ to negatively charged molecules is involved in glomerular basement membrane (GBM) permselectivity. Moreover, the excessive binding of the β₂ variants to other laminins appears to lead to their increased deposition in the GBM. Laminin β₂ also serves as a potentially novel cell-adhesive ligand for integrin α₄β₁. Our findings define biochemical functions of laminin β₂ variants influencing glomerular filtration that may underlie the pathogenesis of isolated nephropathy caused by LAMB2 abnormalities.

An extremely mild clinical course in a case with LAMB2-associated nephritis diagnosed with next-generation sequencing

Biallelic pathogenic variants in the laminin β2 (LAMB2) gene, which encodes laminin β2, are associated with Pierson syndrome characterized by a congenital nephrotic syndrome that rapidly progresses to end-stage renal disease, distinct ocular maldevelopment with bilateral microcoria, and neurodevelopmental deficits. However, the phenotypic spectrum of LAMB2-associated disorder is broader than expected, and cases with milder phenotypes such as isolated congenital or infantile nephrotic syndrome have also been reported. We report a patient with LAMB2-associated renal disorder showing an extremely mild phenotype. A 5-year-old girl presented with asymptomatic proteinuria and hematuria detected by urinalysis screening. She had been previously healthy without any additional renal symptoms. The serum albumin and creatinine levels were normal. Renal biopsy revealed minor glomerular abnormalities with occasional focal mesangial proliferation. Electron microscopy showed no structural changes in the glomerular basement membrane. Targeted sequencing of podocyte-related genes using next-generation sequencing was performed. As a result, previously reported biallelic pathogenic variants of the truncating variant (c.5073_5076dupCCAG) and a splice site variant (c.3797 + 5G > A) in the LAMB2 gene were detected, and the patient was diagnosed with LAMB2-associated renal disorder. Interestingly, a previously reported case with this splicing variant also showed an atypically mild phenotype. We suggest that clinicians should consider LAMB2-associated nephritis as an important differential diagnosis in children with asymptomatic proteinuria and microscopic hematuria if there is no structural change in the glomerular basement membrane. A comprehensive gene-screening system using next-generation sequencing is useful for diagnosing these atypical cases with isolated urine abnormalities.

Integration of genetic and histopathology data in interpretation of kidney disease

For many years renal biopsy has been the gold standard for diagnosis in many forms of kidney disease. It provides rapid, accurate and clinically useful information in most individuals with kidney disease. However, in recent years, other diagnostic modalities have become available that may provide more detailed and specific diagnostic information in addition to, or instead of, renal biopsy. Genomics is one of these modalities. Previously prohibitively expensive and time consuming, it is now increasingly available and practical in a clinical setting for the diagnosis of inherited kidney disease. Inherited kidney disease is a significant cause of kidney disease, in both the adult and paediatric populations. While individual inherited kidney diseases are rare, together they represent a significant burden of disease. Because of the heterogenicity of inherited kidney disease, diagnosis and management can be a challenge and often multiple diagnostic modalities are needed to arrive at a diagnosis. We present updates in genomic medicine for renal disease, how genetic testing integrates with our knowledge of renal histopathology and how the two modalities may interact to enhance patient care.

Endoplasmic Reticulum Calcium Homeostasis in Kidney Disease: Pathogenesis and Therapeutic Targets

Calcium (Ca²⁺) homeostasis is a crucial determinant of cellular function and survival. Endoplasmic reticulum (ER) acts as the largest intracellular Ca²⁺ store that maintains Ca²⁺ homeostasis through the ER Ca²⁺ uptake pump, sarco/ER Ca²⁺ ATPase, ER Ca²⁺ release channels, inositol 1,4,5-trisphosphate receptor channel, ryanodine receptor, and Ca²⁺-binding proteins inside of the ER lumen. Alterations in ER homeostasis trigger ER Ca²⁺ depletion and ER stress, which have been associated with the development of a variety of diseases. In addition, recent studies have highlighted the role of ER Ca²⁺ imbalance caused by dysfunction of sarco/ER Ca²⁺ ATPase, ryanodine receptor, and inositol 1,4,5-trisphosphate receptor channel in various kidney diseases. Despite progress in the understanding of the importance of these ER Ca²⁺ channels, pumps, and binding proteins in the pathogenesis of kidney disease, treatment is still lacking. This mini-review is focused on: i) Ca²⁺ homeostasis in the ER, ii) ER Ca²⁺ dyshomeostasis and apoptosis, and iii) altered ER Ca²⁺ homeostasis in kidney disease, including podocytopathy, diabetic nephropathy, albuminuria, autosomal dominant polycystic kidney disease, and ischemia/reperfusion-induced acute kidney injury.

Understanding What You Have Found: A Family With a Mutation in the LAMA1 Gene With Literature Review

Introduction

Cerebellar dysplasia with cysts (CDC) is an imaging finding which is typically seen with in individuals with dystroglycanopathy. One of the diseases causing this condition is "Poretti-Boltshauser Syndrome; PTBHS" (OMIM #615960). Homozygous or compound heterozygous mutations in the LAMA1 gene cause this disease.

Case presentation

7 years old twin siblings consulted to the medical genetics department because of walking problems and cerebellar examination findings.

Management and Outcome

Clinical and radiological findings of the patient suggested a syndrome with recessive inheritance. Whole exome sequencing (WES) test was performed for definitive diagnosis. As a result of the patient's WES analysis, a homozygous mutation was detected in the LAMA1 gene.

Discussion

When determining the inheritance pattern of genetic diseases, if parents have consanquinity, this situation leads us to recessive inheritance diseases. Even if we are not consanquinity, but they say the same village, it is necessary to pay attention to the diseases of the recessive group. Whole exome sequencing analysis results in large amount of data generation. A good clinical evaluation is required to detect the mutation as a result of large data. To understand what we have found, we need to know what we are looking for.

Treatment of nephrotic syndrome: going beyond immunosuppressive therapy

It is indisputable that immunosuppressive therapy and pathological diagnosis of renal biopsy have greatly improved the prognosis of childhood nephrotic syndrome. Unfortunately, there is no "one-size-fits-all" approach for precise patient stratification and treatment when facing the huge challenges posed by steroid-resistant nephrotic syndrome (SRNS). But genomic medicine has brought a glimmer of light, and the cognition of SRNS has entered a new stage. Based on this, identification of single genetic variants of SRNS has recognized the key role of podocyte injury in its pathogenesis. Targeted treatment of podocyte injury is paramount, and immunosuppressant with podocyte-targeted therapy seems to be more suitable as the first choice for SRNS, that is, we need to pay attention to their additional non-immunosuppressive effects. In the same way, other effect factors of nephrotic syndrome and the related causes of immunosuppressive therapy resistance require us to select reasonable and targeted non-immunosuppressive therapies, instead of only blindly using steroids and immunosuppressants, which may be ineffective and bring significant side effects. This article provides a summary of the clinical value of identification of genetic variants in podocytes and non-immunosuppressive therapy for nephrotic syndrome in children.

Mutations in LAMB2 Are Associated With Albuminuria and Optic Nerve Hypoplasia With Hypopituitarism

CONTEXT

Mutations in LAMB2, encoding the basement membrane protein, laminin β2, are associated with an autosomal recessive disorder characterized by congenital nephrotic syndrome, ocular abnormalities, and neurodevelopmental delay (Pierson syndrome).

CASE DESCRIPTION

This report describes a 12-year-old boy with short stature, visual impairment, and developmental delay who presented with macroscopic hematuria and albuminuria. He had isolated growth hormone deficiency, optic nerve hypoplasia, and a small anterior pituitary with corpus callosum dysgenesis on his cranial magnetic resonance imaging, thereby supporting a diagnosis of optic nerve hypoplasia syndrome. Renal histopathology revealed focal segmental glomerulosclerosis. Using next-generation sequencing on a targeted gene panel for steroid-resistant nephrotic syndrome, compound heterozygous missense mutations were identified in LAMB2 (c.737G>A p.Arg246Gln, c.3982G>C p.Gly1328Arg). Immunohistochemical analysis revealed reduced glomerular laminin β2 expression compared to control kidney and a thin basement membrane on electron microscopy. Laminin β2 is expressed during pituitary development and Lamb2-/- mice exhibit stunted growth, abnormal neural retinae, and here we show, abnormal parenchyma of the anterior pituitary gland.

CONCLUSION

We propose that patients with genetically undefined optic nerve hypoplasia syndrome should be screened for albuminuria and, if present, screened for mutations in LAMB2.

Molecular mechanisms determining severity in patients with Pierson syndrome

Null variants in LAMB2 cause Pierson syndrome (PS), a severe congenital nephrotic syndrome with ocular and neurological defects. Patients' kidney specimens show complete negativity for laminin β2 expression on glomerular basement membrane (GBM). In contrast, missense variants outside the laminin N-terminal (LN) domain in LAMB2 lead to milder phenotypes. However, we experienced cases not showing these typical genotype-phenotype correlations. In this paper, we report six PS patients: four with mild phenotypes and two with severe phenotypes. We conducted molecular studies including protein expression and transcript analyses. The results revealed that three of the four cases with milder phenotypes had missense variants located outside the LN domain and one of the two severe PS cases had a homozygous missense variant located in the LN domain; these variant positions could explain their phenotypes. However, one mild case possessed a splicing site variant (c.3797 + 5G>A) that should be associated with a severe phenotype. Upon transcript analysis, this variant generated some differently sized transcripts, including completely normal transcript, which could have conferred the milder phenotype. In one severe case, we detected the single-nucleotide substitution of c.4616G>A located outside the LN domain, which should be associated with a milder phenotype. However, we detected aberrant splicing caused by the creation of a novel splice site by this single-base substitution. These are novel mechanisms leading to an atypical genotype-phenotype correlation. In addition, all four cases with milder phenotypes showed laminin β2 expression on GBM. We identified novel mechanisms leading to atypical genotype-phenotype correlation in PS.

New Mutation of Coenzyme Q10 Monooxygenase 6 Causing Podocyte Injury in a Focal Segmental Glomerulosclerosis Patient

Background:

Focal segmental glomerulosclerosis (FSGS) is a kidney disease that is commonly associated with proteinuria and the progressive loss of renal function, which is characterized by podocyte injury and the depletion and collapse of glomerular capillary segments. The pathogenesis of FSGS has not been completely elucidated; however, recent advances in molecular genetics have provided increasing evidence that podocyte structural and functional disruption is central to FSGS pathogenesis. Here, we identified a patient with FSGS and aimed to characterize the pathogenic gene and verify its mechanism.

Methods:

Using next-generation sequencing and Sanger sequencing, we screened the causative gene that was linked to FSGS in this study. The patient's total blood RNA was extracted to validate the messenger RNA (mRNA) expression of coenzyme Q₁₀ monooxygenase 6 (COQ6) and validated it by immunohistochemistry. COQ6 knockdown in podocytes was performed in vitro with small interfering RNA, and then, F-actin was determined using immunofluorescence staining. Cell apoptosis was evaluated by flow cytometry, the expression of active caspase-3 was determined by Western blot, and mitochondrial function was detected by MitoSOX.

Results:

Using whole-exome sequencing and Sanger sequencing, we screened a new causative gene, COQ6, NM_182480: exon1: c.G41A: p.W14X. The mRNA expression of COQ6 in the proband showed decreased. Moreover, the expression of COQ6, which was validated by immunohistochemistry, also had the same change in the proband. Finally, we focused on the COQ6 gene to clarify the mechanism of podocyte injury. Flow cytometry showed significantly increased in apoptotic podocytes, and Western blotting showed increases in active caspase-3 in si-COQ6 podocytes. Meanwhile, reactive oxygen species (ROS) levels were increased and F-actin immunofluorescence was irregularly distributed in the si-COQ6 group.

Conclusions:

This study reported a possible mechanism for FSGS and suggested that a new mutation in COQ6, which could cause respiratory chain defect, increase the generation of ROS, destroy the podocyte cytoskeleton, and induce apoptosis. It provides basic theoretical basis for the screening of FSGS in the future.

Genetic testing in steroid-resistant nephrotic syndrome: why, who, when and how?

Steroid-resistant nephrotic syndrome (SRNS) is a common cause of chronic kidney disease in childhood and has a significant risk of rapid progression to end-stage renal disease. The identification of over 50 monogenic causes of SRNS has revealed dysfunction in podocyte-associated proteins in the pathogenesis of proteinuria, highlighting their essential role in glomerular function. Recent technological advances in high-throughput sequencing have enabled indication-driven genetic panel testing for patients with SRNS. The availability of genetic testing, combined with the significant phenotypic variability of monogenic SRNS, poses unique challenges for clinicians when directing genetic testing. This highlights the need for clear clinical guidelines that provide a systematic approach for mutational screening in SRNS. The likelihood of identifying a causative mutation is inversely related to age at disease onset and is increased with a positive family history or the presence of extra-renal manifestations. An unequivocal molecular diagnosis could allow for a personalised treatment approach with weaning of immunosuppressive therapy, avoidance of renal biopsy and provision of accurate, well-informed genetic counselling. Identification of novel causative mutations will continue to unravel the pathogenic mechanisms of glomerular disease and provide new insights into podocyte biology and glomerular function.

Alport syndrome and Pierson syndrome: Diseases of the glomerular basement membrane

The glomerular basement membrane (GBM) is an important component of the kidney's glomerular filtration barrier. Like all basement membranes, the GBM contains type IV collagen, laminin, nidogen, and heparan sulfate proteoglycan. It is flanked by the podocytes and glomerular endothelial cells that both synthesize it and adhere to it. Mutations that affect the GBM's collagen α3α4α5(IV) components cause Alport syndrome (kidney disease with variable ear and eye defects) and its variants, including thin basement membrane nephropathy. Mutations in LAMB2 that impact the synthesis or function of laminin α5β2γ1 (LM-521) cause Pierson syndrome (congenital nephrotic syndrome with eye and neurological defects) and its less severe variants, including isolated congenital nephrotic syndrome. The very different types of kidney diseases that result from mutations in collagen IV vs. laminin are likely due to very different pathogenic mechanisms. A better understanding of these mechanisms should lead to targeted therapeutic approaches that can help people with these rare but important diseases.

Protein-anchoring therapy to target extracellular matrix proteins to their physiological destinations

Endplate acetylcholinesterase (AChE) deficiency is a form of congenital myasthenic syndrome (CMS) caused by mutations in COLQ, which encodes collagen Q (ColQ). ColQ is an extracellular matrix (ECM) protein that anchors AChE to the synaptic basal lamina. Biglycan, encoded by BGN, is another ECM protein that binds to the dystrophin-associated protein complex (DAPC) on skeletal muscle, which links the actin cytoskeleton and ECM proteins to stabilize the sarcolemma during repeated muscle contractions. Upregulation of biglycan stabilizes the DPAC. Gene therapy can potentially ameliorate any disease that can be recapitulated in cultured cells. However, the difficulty of tissue-specific and developmental stage-specific regulated expression of transgenes, as well as the difficulty of introducing a transgene into all cells in a specific tissue, prevents us from successfully applying gene therapy to many human diseases. In contrast to intracellular proteins, an ECM protein is anchored to the target tissue via its specific binding affinity for protein(s) expressed on the cell surface within the target tissue. Exploiting this unique feature of ECM proteins, we developed protein-anchoring therapy in which a transgene product expressed even in remote tissues can be delivered and anchored to a target tissue using specific binding signals. We demonstrate the application of protein-anchoring therapy to two disease models. First, intravenous administration of adeno-associated virus (AAV) serotype 8-COLQ to Colq-deficient mice, resulting in specific anchoring of ectopically expressed ColQ-AChE at the NMJ, markedly improved motor functions, synaptic transmission, and the ultrastructure of the neuromuscular junction (NMJ). In the second example, Mdx mice, a model for Duchenne muscular dystrophy, were intravenously injected with AAV8-BGN. The treatment ameliorated motor deficits, mitigated muscle histopathologies, decreased plasma creatine kinase activities, and upregulated expression of utrophin and DAPC component proteins. We propose that protein-anchoring therapy could be applied to hereditary/acquired defects in ECM and secreted proteins, as well as therapeutic overexpression of such factors.

Laminin-521 Protein Therapy for Glomerular Basement Membrane and Podocyte Abnormalities in a Model of Pierson Syndrome

Background Laminin α5β2γ1 (LM-521) is a major component of the GBM. Mutations in LAMB2 that prevent LM-521 synthesis and/or secretion cause Pierson syndrome, a rare congenital nephrotic syndrome with diffuse mesangial sclerosis and ocular and neurologic defects. Because the GBM is uniquely accessible to plasma, which permeates endothelial cell fenestrae, we hypothesized that intravenous delivery of LM-521 could replace the missing LM-521 in the GBM of Lamb2 mutant mice and restore glomerular permselectivity.Methods We injected human LM-521 (hLM-521), a macromolecule of approximately 800 kD, into the retro-orbital sinus of Lamb2-/- pups daily. Deposition of hLM-521 into the GBM was investigated by fluorescence microscopy. We assayed the effects of hLM-521 on glomerular permselectivity by urinalysis and the effects on podocytes by desmin immunostaining and ultrastructural analysis of podocyte architecture.Results Injected hLM-521 rapidly and stably accumulated in the GBM of all glomeruli. Super-resolution imaging showed that hLM-521 accumulated in the correct orientation in the GBM, primarily on the endothelial aspect. Treatment with hLM-521 greatly reduced the expression of the podocyte injury marker desmin and attenuated the foot process effacement observed in untreated pups. Moreover, treatment with hLM-521 delayed the onset of proteinuria but did not prevent nephrotic syndrome, perhaps due to its absence from the podocyte aspect of the GBM.Conclusions These studies show that GBM composition and function can be altered in vivovia vascular delivery of even very large proteins, which may advance therapeutic options for patients with abnormal GBM composition, whether genetic or acquired.

Monogenic Causes of Proteinuria in Children

Glomerular disease is a common cause for proteinuria and chronic kidney disease leading to end-stage renal disease requiring dialysis or kidney transplantation in children. Nephrotic syndrome in children is diagnosed by the presence of a triad of proteinuria, hypoalbuminemia, and edema. Minimal change disease is the most common histopathological finding in children and adolescents with nephrotic syndrome. Focal segmental sclerosis is also found in children and is the most common pathological finding in patients with monogenic causes of nephrotic syndrome. Current classification system for nephrotic syndrome is based on response to steroid therapy as a majority of patients develop steroid sensitive nephrotic syndrome regardless of histopathological diagnosis or the presence of genetic mutations. Recent studies investigating the genetics of nephrotic syndrome have shed light on the pathophysiology and mechanisms of proteinuria in nephrotic syndrome. Gene mutations have been identified in several subcellular compartments of the glomerular podocyte and play a critical role in mitochondrial function, actin cytoskeleton dynamics, cell-matrix interactions, slit diaphragm, and podocyte integrity. A subset of genetic mutations are known to cause nephrotic syndrome that is responsive to immunosuppressive therapy but clinical data are limited with respect to renal prognosis and disease progression in a majority of patients. To date, more than 50 genes have been identified as causative factors in nephrotic syndrome in children and adults. As genetic testing becomes more prevalent and affordable, we expect rapid advances in our understanding of mechanisms of proteinuria and genetic diagnosis will help direct future therapy for individual patients.

Skeletal impairment in Pierson syndrome: Is there a role for lamininβ2 in bone physiology?

INTRODUCTION

Pierson syndrome is caused by a mutation of LAMB2, encoding for laminin β2. Clinical phenotype is variable but usually associates congenital nephrotic syndrome (CNS) and ocular abnormalities. Neuromuscular impairment has also been described.

METHODS

We report on a 15-year old girl, suffering from Pierson Syndrome, who developed severe bone deformations during puberty. This patient initially displayed CNS and microcoria, leading to the clinical diagnosis of Pierson syndrome. Genetic analysis revealed a truncating mutation and a splice site mutation of LAMB2. The patient received a renal transplantation (R-Tx) at the age of 3. After R-Tx, renal evolution was simple, the patient receiving low-dose corticosteroids, tacrolimus and mycophenolate mofetil. At the age of 12, bone deformations progressively appeared. At the time of bone impairment, renal function was subnormal (glomerular filtration rate using iohexol clearance 50mL/min per 1.73m²), and parameters of calcium/phosphate metabolism were normal (calcium 2.45mmol/L, phosphorus 1.30mmol/L, PTH 81ng/L, ALP 334U/L, 25OH-D 73nmol/L). Radiographs showed major deformations such as scoliosis, genu varum and diffuse epiphyseal abnormalities. A high resolution scanner (HR-pQCT) was performed, demonstrating a bone of "normal low" quantity and quality; major radial and cubital deformations were observed. Stainings of laminin β2 were performed on bone and renal samples from the patient and healthy controls: as expected, laminin β2 was expressed in the control kidney but not in the patient's renal tissue, and a similar pattern was observed in bone.

CONCLUSION

This is the first case of skeletal impairment ever described in Pierson syndrome. Integrin α3β1, receptor for laminin β2, are found in podocytes and osteoblasts, and the observation of both the presence of laminin β2 staining in healthy bone and its absence in the patient's bone raises the question of a potential role of laminin β2 in bone physiology.

Basement Membrane Defects in Genetic Kidney Diseases

The glomerular basement membrane (GBM) is a specialized structure with a significant role in maintaining the glomerular filtration barrier. This GBM is formed from the fusion of two basement membranes during development and its function in the filtration barrier is achieved by key extracellular matrix components including type IV collagen, laminins, nidogens, and heparan sulfate proteoglycans. The characteristics of specific matrix isoforms such as laminin-521 (α5β2γ1) and the α3α4α5 chain of type IV collagen are essential for the formation of a mature GBM and the restricted tissue distribution of these isoforms makes the GBM a unique structure. Detailed investigation of the GBM has been driven by the identification of inherited abnormalities in matrix proteins and the need to understand pathogenic mechanisms causing severe glomerular disease. A well-described hereditary GBM disease is Alport syndrome, associated with a progressive glomerular disease, hearing loss, and lens defects due to mutations in the genes COL4A3, COL4A4, or COL4A5. Other proteins associated with inherited diseases of the GBM include laminin β2 in Pierson syndrome and LMX1B in nail patella syndrome. The knowledge of these genetic mutations associated with GBM defects has enhanced our understanding of cell-matrix signaling pathways affected in glomerular disease. This review will address current knowledge of GBM-associated abnormalities and related signaling pathways, as well as discussing the advances toward disease-targeted therapies for patients with glomerular disease.

Pathogenicity of a Human Laminin β2 Mutation Revealed in Models of Alport Syndrome

Pierson syndrome is a congenital nephrotic syndrome with eye and neurologic defects caused by mutations in laminin β2 (LAMB2), a major component of the glomerular basement membrane (GBM). Pathogenic missense mutations in human LAMB2 cluster in or near the laminin amino-terminal (LN) domain, a domain required for extracellular polymerization of laminin trimers and basement membrane scaffolding. Here, we investigated an LN domain missense mutation, LAMB2-S80R, which was discovered in a patient with Pierson syndrome and unusually late onset of proteinuria. Biochemical data indicated that this mutation impairs laminin polymerization, which we hypothesized to be the cause of the patient's nephrotic syndrome. Testing this hypothesis in genetically altered mice showed that the corresponding amino acid change (LAMB2-S83R) alone is not pathogenic. However, expression of LAMB2-S83R significantly increased the rate of progression to kidney failure in a Col4a3^-/- mouse model of autosomal recessive Alport syndrome and increased proteinuria in Col4a5^+/- females that exhibit a mild form of X-linked Alport syndrome due to mosaic deposition of collagen α3α4α5(IV) in the GBM. Collectively, these data show the pathogenicity of LAMB2-S80R and provide the first evidence of genetic modification of Alport phenotypes by variation in another GBM component. This finding could help explain the wide range of Alport syndrome onset and severity observed in patients with Alport syndrome, even for family members who share the same COL4 mutation. Our results also show the complexities of using model organisms to investigate genetic variants suspected of being pathogenic in humans.

Loss of podocalyxin causes a novel syndromic type of congenital nephrotic syndrome

Many cellular structures directly imply specific biological functions. For example, normal slit diaphragm structures that extend from podocyte foot processes ensure the filtering function of renal glomeruli. These slits are covered by a number of surface proteins, such as nephrin, podocin, podocalyxin and CD2AP. Here we report a human patient presenting with congenital nephrotic syndrome, omphalocele and microcoria due to two loss-of-function mutations in PODXL, which encodes podocalyxin, inherited from each parent. This set of symptoms strikingly mimics previously reported mouse Podxl^−/− embryos, emphasizing the essential function of PODXL in mammalian kidney development and highlighting this patient as a human PODXL-null model. The results underscore the utility of current genomics approaches to provide insights into the genetic mechanisms of human disease traits through molecular diagnosis.

Partial uniparental isodisomy of chromosome 16 unmasks a deleterious biallelic mutation in IFT140 that causes Mainzer-Saldino syndrome

BACKGROUND

The ciliopathies represent an umbrella group of >50 clinical entities that share both clinical features and molecular etiology underscored by structural and functional defects of the primary cilium. Despite the advances in gene discovery, this group of entities continues to pose a diagnostic challenge, in part due to significant genetic and phenotypic heterogeneity and variability. We consulted a pediatric case from asymptomatic, non-consanguineous parents who presented as a suspected ciliopathy due to a constellation of retinal, renal, and skeletal findings.

RESULTS

Although clinical panel sequencing of genes implicated in nephrotic syndromes yielded no likely causal mutation, an oligo-SNP microarray identified a ~20-Mb region of homozygosity, with no altered gene dosage, on chromosome 16p13. Intersection of the proband's phenotypes with known disease genes within the homozygous region yielded a single candidate, IFT140, encoding a retrograde intraflagellar transport protein implicated previously in several ciliopathies, including the phenotypically overlapping Mainzer-Saldino syndrome (MZSDS). Sanger sequencing yielded a maternally inherited homozygous c.634G>A; p.Gly212Arg mutation altering the exon 6 splice donor site. Functional studies in cells from the proband showed that the locus produced two transcripts: a majority message containing a mis-splicing event that caused a premature termination codon and a minority message homozygous for the p.Gly212Arg allele. Zebrafish in vivo complementation studies of the latter transcript demonstrated a loss of function effect. Finally, we conducted post-hoc trio-based whole exome sequencing studies to (a) test the possibility of other causal loci in the proband and (b) explain the Mendelian error of segregation for the IFT140 mutation. We show that the proband harbors a chromosome 16 maternal heterodisomy, with segmental isodisomy at 16p13, likely due to a meiosis I error in the maternal gamete.

CONCLUSIONS

Using clinical phenotyping combined with research-based genetic and functional studies, we have characterized a recurrent IFT140 mutation in the proband; together, these data are consistent with MZSDS. Additionally, we report a rare instance of a uniparental isodisomy unmasking a deleterious mutation to cause a ciliary disorder.

Nephron development and extrarenal features in a child with congenital nephrotic syndrome caused by null LAMB2 mutations

BACKGROUND

Congenital nephrotic syndrome (CNS) is a rare disorder caused by various structural and developmental defects of glomeruli. It occurs typically as an isolated kidney disorder but associates sometimes with other systemic, extrarenal manifestations.

CASE PRESENTATIONS

An infant presented with severe CNS, which progressed rapidly to renal failure at age of 3 months and death at 27 months. The clinical phenotypes and genetic causes were studied, including the renal pathology at autopsy. Besides the CNS, the affected child had remarkable right-side predominant eye-ball hypoplasia with bilateral anterior chamber dysgenesis (microcoria). Brain MRI revealed grossly normal development in the cerebrum, cerebellum, and brain stem. Auditory brainstem responses were bilaterally blunted, suggesting a defective auditory system. At autopsy, both kidneys were mildly atrophied with persistent fetal lobulation. Microscopic examination showed a diffuse global sclerosis. However, despite of the smaller size of glomeruli, the nephron number remained similar to that of the age-matched control. Whole-exome sequencing revealed that the affected child was compound heterozygous for novel truncating LAMB2 mutations: a 4-bp insertion (p.Gly1693Alafs*8) and a splicing donor-site substitution (c.1225 + 1G > A), presumably deleting the coiled-coil domains that form the laminin 5-2-1 heterotrimer complex.

CONCLUSIONS

Our case represents a variation of Pierson syndrome that accompanies CNS with unilateral ocular hypoplasia. The average number but smaller glomeruli could reflect either mal-development or glomerulosclerosis. Heterogeneous clinical expression of LAMB2 defects may associate with the difference in fetal β1 subtype compensation among affected tissues. Further study is necessary to evaluate incidence and features of auditory defect under LAMB2 deficiency.

Genetics of hereditary nephrotic syndrome: a clinical review

Advances in podocytology and genetic techniques have expanded our understanding of the pathogenesis of hereditary steroid-resistant nephrotic syndrome (SRNS). In the past 20 years, over 45 genetic mutations have been identified in patients with hereditary SRNS. Genetic mutations on structural and functional molecules in podocytes can lead to serious injury in the podocytes themselves and in adjacent structures, causing sclerotic lesions such as focal segmental glomerulosclerosis or diffuse mesangial sclerosis. This paper provides an update on the current knowledge of podocyte genes involved in the development of hereditary nephrotic syndrome and, thereby, reviews genotype-phenotype correlations to propose an approach for appropriate mutational screening based on clinical aspects.

A novel mutation of laminin β2 (LAMB2) in two siblings with renal failure

This report describes a novel mutation of LAMB2, the gene associated with Pierson syndrome (microcoria-congenital nephrosis syndrome), in two female siblings. The c.970T>C p.(Cys324Arg) mutation in the LAMB2 gene affects one of the eight highly conserved cysteine residues within the first EGF-like module of the laminin β2 protein. These residues form disulfide bonds in order to achieve a correct 3D structure of the protein. The reported phenotype is considered a relatively mild variant of Pierson syndrome and is associated with later-onset (18 months) therapy-resistant nephrotic syndrome leading to renal failure, and ocular abnormalities consisting of high myopia, microcoria, diverse retinal abnormalities, hence a low level of visual acuity. Importantly, the reported LAMB2 mutation was associated with normal neurological development in both siblings.

CONCLUSION

this report presents the variability of the renal, ocular and neurological phenotypes associated with LAMB2 mutations and underscores the importance of ophthalmologic examination in all children with unexplained renal insufficiency or nephrotic syndrome. What is known • LAMB2 mutations are associated with Pierson syndrome • Pierson syndrome is associated with congenital nephrotic syndrome, microcoria and neurological deficits What is new • A novel mutation in the LAMB2 gene in two female siblings • Genotype and clinical phenotype description of a novel LAMB2 mutation.

Mesencephalic Astrocyte-Derived Neurotrophic Factor as a Urine Biomarker for Endoplasmic Reticulum Stress-Related Kidney Diseases

Endoplasmic reticulum (ER) stress and disrupted proteostasis contribute to the pathogenesis of a variety of glomerular and tubular diseases. Thus, it is imperative to develop noninvasive biomarkers for detecting ER stress in podocytes or tubular cells in the incipient stage of disease, when a kidney biopsy is not yet clinically indicated. Mesencephalic astrocyte-derived neurotrophic factor (MANF) localizes to the ER lumen and is secreted in response to ER stress in several cell types. Here, using mouse models of human nephrotic syndrome caused by mutant laminin β2 protein-induced podocyte ER stress and AKI triggered by tunicamycin- or ischemia-reperfusion-induced tubular ER stress, we examined MANF as a potential urine biomarker for detecting ER stress in podocytes or renal tubular cells. ER stress upregulated MANF expression in podocytes and tubular cells. Notably, urinary MANF excretion concurrent with podocyte or tubular cell ER stress preceded clinical or histologic manifestations of the corresponding disease. Thus, MANF can potentially serve as a urine diagnostic or prognostic biomarker in ER stress-related kidney diseases to help stratify disease risk, predict disease progression, monitor treatment response, and identify subgroups of patients who can be treated with ER stress modulators in a highly targeted manner.

The role of laminins in the organization and function of neuromuscular junctions

The synapse between motor neurons and skeletal muscle is known as the neuromuscular junction (NMJ). Proper alignment of presynaptic and post-synaptic structures of motor neurons and muscle fibers, respectively, is essential for efficient motor control of skeletal muscles. The synaptic cleft between these two cells is filled with basal lamina. Laminins are heterotrimer extracellular matrix molecules that are key members of the basal lamina. Laminin α4, α5, and β2 chains specifically localize to NMJs, and these laminin isoforms play a critical role in maintenance of NMJs and organization of synaptic vesicle release sites known as active zones. These individual laminin chains exert their role in organizing NMJs by binding to their receptors including integrins, dystroglycan, and voltage-gated calcium channels (VGCCs). Disruption of these laminins or the laminin-receptor interaction occurs in neuromuscular diseases including Pierson syndrome and Lambert-Eaton myasthenic syndrome (LEMS). Interventions to maintain proper level of laminins and their receptor interactions may be insightful in treating neuromuscular diseases and aging related degeneration of NMJs.

The etiology of congenital nephrotic syndrome: current status and challenges

BACKGROUND

Congenital nephrotic syndrome (CNS), defined as heavy proteinuria, hypoalbuminemia, hyperlipidemia and edema presenting in the first 0-3 months of life, may be caused by congenital syphilis, toxoplasmosis, or congenital viral infections (such as cytomegalovirus). However, the majority of CNS cases are caused by monogenic defects of structural proteins that form the glomerular filtration barrier in the kidneys. Since 1998, an increasing number of genetic defects have been identified for their involvements in the pathogenesis of CNS, including NPHS1, NPHS2, WT1, PLCE1, and LAMB2.

DATA SOURCES

We searched databases such as PubMed, Elsevier and Wanfang with the following key words: congenital nephrotic syndrome, proteinuria, infants, neonate, congenital infection, mechanism and treatment; and we selected those publications written in English that we judged to be relevant to the topic of this review.

RESULTS

Based on the data present in the literature, we reviewed the following topics: 1) Infection associated CNS including congenital syphilis, congenital toxoplasmosis, and congenital cytomegalovirus infection; 2) genetic CNS including mutation of NPHS1 (Nephrin), NPHS2 (Podocin), WT1, LAMB2 (Laminin-β2), PLCE1 (NPHS3); 3) Other forms of CNS including maternal systemic lupus erythematosus, mercury poisoning, renal vein thrombosis, neonatal alloimmunization against neutral endopeptidase.

CONCLUSION

At present, the main challenge in CNS is to identify the cause of disease for individual patients. To make a definitive diagnosis, with the exclusion of infection-related CNS and maternal-associated disorders, pathology, family history, inheritance mode, and other accompanying congenital malformations are sometimes, but not always, useful indicators for diagnosing genetic CNS. Next-generation sequencing would be a more effective method for diagnosing genetic CNS in some patients, however, there are still some challenges with next-generation sequencing that need to be resolved in the future.