Focal segmental glomerulosclerosis and medullary nephrocalcinosis in children with ADCK4 mutations

Long-term nephrotic syndrome recurrence risk of kidney transplantation in two siblings with ADCK4-associated glomerulopathy

BACKGROUND

Mutations in the ADCK4 gene cause steroid-resistant nephrotic syndrome (NS), namely ADCK4-associated glomerulopathy. Reportedly, 38.5% of patients with ADCK4-associated glomerulopathy had end-stage renal disease (ESRD) at the time of diagnosis of ADCK4-associated glomerulopathy, requiring renal replacement therapy, such as dialysis and kidney transplantation. However, long-term NS recurrence risk of kidney transplantation in patients with ADCK4-associated glomerulopathy is unknown.

METHODS

The clinical data and mutations in ADCK4 of two siblings with steroid-resistant NS were collected. The long-term prognosis of the two siblings who received kidney transplantation was evaluated.

RESULTS

We describe two siblings with ADCK4-associated glomerulopathy who received deceased donor kidney transplantation and showed no clinical evidence of recurrence of NS during more than 10 years of follow-up.

CONCLUSIONS

This suggests that long-term NS recurrence risk of kidney transplantation is low in patients with ADCK4-associated glomerulopathy who progress to ESRD.

Clinical features and gene variation analysis of COQ8B nephropathy: Report of seven cases

OBJECTIVE

COQ8B nephropathy is a relatively rare autosomal recessive kidney disease characterized by proteinuria and a progressive deterioration of renal function, eventually leading to end-stage renal disease (ESRD). The objective is to study the characteristics and correlation between the genotype and the clinical phenotype of COQ8B nephropathy.

METHODS

This is a retrospective study focusing on the clinical characteristics of seven COQ8B nephropathy patients diagnosed by gene sequencing. Basic clinical information, clinical manifestations, examinations, imaging, genomes, pathology, treatments, and prognosis of the patients were reviewed.

RESULTS

Of the seven patients, two were male children and five were female children. The median age at the disease onset was 5 years and 3 months. The initial main clinical manifestations were proteinuria and renal insufficiency. Four patients had severe proteinuria, four had focal segmental glomerulosclerosis (FSGS) diagnosed by a renal biopsy, and two had nephrocalcinosis after an ultrasound was performed on them. There were no other clinical manifestations such as neuropathy, muscle atrophy, and so on in all of them. Their gene mutations were all exon variants, which were classified as heterozygous or homozygous variants by performing family verification analysis. Compound heterozygous variants were predominant in all, and all gene variants were inherited from their parents. One novel mutation, c.1465c>t, was found in this study. This gene mutation resulted from changes in the amino acid sequence, thus leading to an abnormal protein structure. Two patients with early diagnosis of COQ8B nephropathy presented with no renal insufficiency and were treated with oral coenzyme Q10 (CoQ10), and they maintained normal renal function. For the remaining five who were treated with CoQ10 following renal insufficiency, the deterioration of renal function could not be reversed, and they progressed to ESRD within a short time (median time: 7 months). A follow-up of these patients showed normal renal function with a CoQ10 supplement.

CONCLUSION

For unexplained proteinuria, renal insufficiency, or steroid-resistant nephrotic syndrome, gene sequencing should be considered, in addition to renal biopsy, as early as possible. Timely diagnosis of COQ8B nephropathy and early supplementation of sufficient CoQ10 can help control the progression of the disease and significantly improve the prognosis.

COQ8B glomerular nephropathy: Outcomes after kidney transplantation and analysis of characteristics in Chinese population

BACKGROUND

Mutation in the COQ8B gene can cause COQ8B glomerular nephropathy (COQ8B-GN), which is rare and associated with steroid-resistant nephrotic syndrome (SRNS) as well as rapid progression to end-stage renal disease (ESRD). The aim of this study was to analyze the prognosis and recurrence risk of COQ8B-GN in patients after kidney transplantation (KTx) and summarize the characteristics of the Chinese population.

METHODS

A retrospective study included four cases treated in our hospital with a diagnosis of COQ8B-GN. Chinese and foreign studies were searched from database inception to February 2022.

RESULTS

A total of four cases were included, with the age of onset ranging from 4 to 9 years. The initial presentations were SRNS and asymptomatic proteinuria. Only one had an extrarenal manifestation (thyroid cyst). All patients progressed to ESRD at a mean time of 42 months after onset. With a total follow-up time ranging from 12 to 87 months, three of them had received transplantation. While one case needed a second KTx due to graft failure caused by chronic rejection, two recipients had excellent graft function. No recurrence in allograft was observed. There have been 18 cases of KTx recipients reported globally with follow-up information. Except for two cases of graft failure caused by hyperacute rejection and chronic rejection, respectively, the rest all had good graft function without recurrence. In addition, 44 cases of COQ8B-GN in the Chinese population were identified. At the onset, 75% of the patients were aged ≤10 years with initial symptoms of asymptomatic proteinuria, nephrotic syndrome (NS), or SRNS. By the time of literature publication, 59% of patients had progressed to ESRD (mean age of 10.3 ± 3.6 years). The median time from onset to ESRD was 21 months. Renal pathology mainly showed focal segmental glomerulosclerosis (FSGS), accounting for 61.8% of all biopsies, followed by mesangial proliferative glomerulonephritis (20.6%). The first three prevalent mutations in the COQ8B gene among the Chinese population were c. 748G>C, c. 737G>A, and c. 532C>T.

CONCLUSION

COQ8B-GN in the Chinese population may present with asymptomatic proteinuria, NS, or SRNS initially, with most onsets before the age of 10 years. A lot of patients progress to ESRD in early adolescence. FSGS on biopsy and c. 748G>C in the genetic test are the most frequently seen in Chinese COQ8B-GN patients. KTx is feasible for patients with ESRD due to the low risk of recurrence, but we should pay attention to graft rejection.

Primary coenzyme Q10 nephropathy, a potentially treatable form of steroid-resistant nephrotic syndrome

Steroid-resistant nephrotic syndrome (SRNS) is a genetically heterogeneous kidney disease that is the second most frequent cause of kidney failure in the first 2 decades of life. Despite the identification of mutations in more than 39 genes as causing SRNS, and the localization of its pathogenesis to glomerular podocytes, the disease mechanisms of SRNS remain poorly understood and no universally safe and effective therapy exists to treat patients with this condition. Recently, genetic research has identified a subgroup of SRNS patients whose kidney pathology is caused by primary coenzyme Q10 (CoQ10) deficiency due to recessive mutations in genes that encode proteins in the CoQ10 biosynthesis pathway. Clinical and preclinical studies show that primary CoQ10 deficiency may be responsive to treatment with CoQ10 supplements bypassing the biosynthesis defects. Coenzyme Q10 is an essential component of the mitochondrial respiratory chain, where it transports electrons from complexes I and II to complex III. Studies in yeast and mammalian model systems have recently identified the molecular functions of the individual CoQ10 biosynthesis complex proteins, validated these findings, and provided an impetus for developing therapeutic compounds to replenish CoQ10 levels in the tissues/organs and thus prevent the destruction of tissues due to mitochondrial OXPHOS deficiencies. In this review, we will summarize the clinical findings of the kidney pathophysiology of primary CoQ10 deficiencies and discuss recent advances in the development of therapies to counter CoQ10 deficiency in tissues.

Whole-exome sequencing reveals a novel homozygous mutation in the COQ8B gene associated with nephrotic syndrome

Nephrotic syndrome arising from monogenic mutations differs substantially from acquired ones in their clinical prognosis, progression, and disease management. Several pathogenic mutations in the COQ8B gene are known to cause nephrotic syndrome. Here, we used the whole-exome sequencing (WES) technology to decipher the genetic cause of nephrotic syndrome (CKD stage-V) in a large affected consanguineous family. Our study exposed a novel missense homozygous mutation NC_000019.9:g.41209497C > T; NM_024876.4:c.748G > A; NP_079152.3:p.(Asp250Asn) in the 9th exon of the COQ8B gene, co-segregated well with the disease phenotype. Our study provides the first insight into this homozygous condition, which has not been previously reported in 1000Genome, ClinVar, ExAC, and genomAD databases. In addition to the pathogenic COQ8B variant, the WES data also revealed some novel and recurrent mutations in the GLA, NUP107, COQ2, COQ6, COQ7 and COQ9 genes. The novel variants observed in this study have been submitted to the ClinVar database and are publicly available online with the accessions: SCV001451361.1, SCV001451725.1 and SCV001451724.1. Based on the patient's clinical history and genomic data with in silico validation, we conclude that pathogenic mutation in the COQ8B gene was causing kidney failure in an autosomal recessive manner. We recommend WES technology for genetic testing in such a consanguineous family to not only prevent the future generation, but early detection can help in disease management and therapeutic interventions.

Primary Coenzyme Q deficiencies: A literature review and online platform of clinical features to uncover genotype-phenotype correlations

Primary Coenzyme Q (CoQ) deficiencies are clinically heterogeneous conditions and lack clear genotype-phenotype correlations, complicating diagnosis and prognostic assessment. Here we present a compilation of all the symptoms and patients with primary CoQ deficiency described in the literature so far and analyse the most common clinical manifestations associated with pathogenic variants identified in the different COQ genes. In addition, we identified new associations between the age of onset of symptoms and different pathogenic variants, which could help to a better diagnosis and guided treatment. To make these results useable for clinicians, we created an online platform (https://coenzymeQbiology.github.io/clinic-CoQ-deficiency) about clinical manifestations of primary CoQ deficiency that will be periodically updated to incorporate new information published in the literature. Since CoQ primary deficiency is a rare disease, the available data are still limited, but as new patients are added over time, this tool could become a key resource for a more efficient diagnosis of this pathology.

Urinary coenzyme Q10 as a diagnostic biomarker and predictor of remission in a patient with ADCK4-associated Glomerulopathy: a case report

BACKGROUND

AarF domain-containing kinase 4 (ADCK4)-associated glomerulopathy is a mitochondrial nephropathy caused by mutations in the ADCK4 gene, which disrupt coenzyme Q10 biosynthesis.

CASE PRESENTATION

We report the case of a 25-year-old female patient with ADCK4-associated glomerulopathy presenting with proteinuria (and with no additional systemic symptoms). A known missense substitution c.737G > A (p.S246N) and a novel frameshift c.577-600del (p.193-200del) mutation were found. We followed the patient for 24 months during supplementation with coenzyme Q10 (20 mg/kg/d - 30 mg/kg/d) and describe the clinical course. In addition, we measured serum and urine coenzyme Q10 levels before and after coenzyme Q10 supplementation and compared them with those of healthy control subjects. The patient's urinary coenzyme Q10 to creatinine ratio was higher than that of healthy controls before coenzyme Q10 supplementation, but decreased consistently with proteinuria after coenzyme Q10 supplementation.

CONCLUSIONS

Although the use of urinary coenzyme Q10 as a diagnostic biomarker and predictor of clinical remission in patients with ADCK4-associated glomerulopathy should be confirmed by larger studies, we recommend measuring urinary coenzyme Q10 in patients with isolated proteinuria of unknown cause, since it may provide a diagnostic clue to mitochondrial nephropathy.

Current understandings in treating children with steroid-resistant nephrotic syndrome

Steroid-resistant nephrotic syndrome (SRNS) remains a challenge for paediatric nephrologists. SRNS is viewed as a heterogeneous disease entity including immune-based and monogenic aetiologies. Because SRNS is rare, treatment strategies are individualized and vary among centres of expertise. Calcineurin inhibitors (CNI) have been effectively used to induce remission in patients with immune-based SRNS; however, there is still no consensus on treating children who become either CNI-dependent or CNI-resistant. Rituximab is a steroid-sparing agent for patients with steroid-sensitive nephrotic syndrome, but its efficacy in SRNS is controversial. Recently, several novel monoclonal antibodies are emerging as treatment option, but their efficacy remains to be seen. Non-immune therapies, such as angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers, have been proven efficacious in children with SRNS and are recommended as adjuvant agents. This review summarizes and discusses our current understandings in treating children with idiopathic SRNS.

Mitochondrial Disease and the Kidney With a Special Focus on CoQ10 Deficiency

Mitochondrial cytopathies include a heterogeneous group of diseases that are characterized by impaired oxidative phosphorylation, leading to multi-organ involvement and progressive clinical deterioration. Most mitochondrial cytopathies that cause kidney symptoms are characterized by tubular defects, but glomerular, tubulointerstitial, and cystic diseases have also been described. Mitochondrial cytopathies can result from mitochondrial or nuclear DNA mutations. Early recognition of defects in the coenzyme Q10 (CoQ10) biosynthesis is important, as patients with primary CoQ10 deficiency may be responsive to treatment with oral CoQ10 supplementation, in contrast to most mitochondrial diseases. A literature search was conducted to investigate kidney involvement in genetic mitochondrial cytopathies and to identify mitochondrial and nuclear DNA mutations involved in mitochondrial kidney disease. Furthermore, we identified all reported cases to date with a CoQ10 deficiency with glomerular involvement, including 3 patients with variable renal phenotypes in our clinic. To date, 144 patients from 95 families with a primary CoQ10 deficiency and glomerular involvement have been described based on mutations in PDSS1, PDSS2, COQ2, COQ6, and COQ8B/ADCK4. This review provides an overview of kidney involvement in genetic mitochondrial cytopathies with a special focus on CoQ10 deficiency.

The role of novel COQ8B mutations in glomerulopathy and related kidney defects

BACKGROUND AND OBJECTIVES

Glomerulopathies affect kidney glomeruli and can lead to end-stage renal disease if untreated. Clinical and experimental evidence have identified numerous (>20) genetic mutations in the mitochondrial coenzyme Q8B protein (COQ8B) primarily associated with nephrotic syndrome. Yet, little else is understood about COQ8B activity in renal pathogenesis and its role in mitochondrial dysfunction. We identified additional novel COQ8B mutations in a glomerulopathy patient and aimed to define the potential structural and functional defects of COQ8B mutations.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

Whole exome sequencing was performed on a Hispanic female presenting with proteinuria. Novel mutations in the COQ8B gene were identified. The effects of mutation on protein function, mitochondrial morphology, and disease progression were investigated by histopathology, transmission electron microscopy, homology modeling, and in silico structural analysis.

RESULTS

We have characterized the pathophysiology of novel COQ8B mutations, compound heterozygous for two alterations c.1037T>G (p.I346S), and c.1560G>A (p.W520X), in the progression of proteinuria in a Hispanic female. Histopathology revealed defects in podocyte structure and mitochondrial morphology. In silico and computation analyses highlight possible structural origins of COQ8B dysfunction in the presence of mutations.

CONCLUSIONS

Novel mutations in COQ8B present promising biomarkers for the early detection and therapeutic targeting of mitochondrial glomerulopathy. Insights from structural modeling suggest roles of mutation-dependent alterations in COQ8B allosteric regulation, protein folding, or stability in renal pathogenesis.

Transcription factor Kruppel-like factor 5 positively regulates the expression of AarF domain containing kinase 4

AarF domain containing kinase 4 (ADCK4) is identified as a candidate gene associated with hereditary nephrotic syndrome (NS). Kruppel-like factor 5 (KLF5) is reported to promote podocyte survival by blocking the ERK/p38 MAPK pathways. Both ADCK4 and KLF5 are involved in the occurrence and development of podocyte disease, but their interaction remains unclear. Firstly, we found that the mRNA levels of ADCK4 and KLF5 decreased in NS patients, and both levels showed an obvious linear relationship. Secondly, we cloned the ADCK4 promoter region and examined its promoter activity in Hela, A549, and HEK 293 cell lines. Deletion analysis showed that the region - 116/- 4 relative to the transcriptional start site (TSS) was the core region of ADCK4 promoter. Thirdly, mutation analysis showed that putative binding sites for KLF5 contributed to the ADCK4 promoter activity. In HEK293 cells, we found that KLF5 upregulated the mRNA and protein levels of ADCK4. Finally, our chromatin immunoprecipitation assay found that KLF5 could bind to the specific region of ADCK4 promoter. These results showed that KLF5 can positively regulate the transcriptional activity of ADCK4.

Early-onset COQ8B (ADCK4) glomerulopathy in a child with isolated proteinuria: a case report and literature review

Background

Herein, a 3-year-old boy presented with hidden-onset isolated proteinuria was reported. The disease was induced by COQ8B (previously termed ADCK4) compound heterozygous variants, including c.[271C > T] and c.[737G > A], which were inherited from his father and mother, respectively.

Case presentation

The patient visited our clinic due to non-nephrotic range proteinuria for 3 months, but no obvious abnormality was detected in the vital signs or laboratory test results. Renal histopathology revealed mitochondrial nephropathy, which manifested as mild glomerular abnormalities under light microscope, together with mitochondrial proliferation and hypertrophy and crowded arrangement under electron microscope. As suggested by whole exome sequencing, the patient inherited the COQ8B compound heterozygous variants from both of his parents who showed normal phenotype. After literature review, it was confirmed that one of the variant site (c.[271C > T]) had not been reported among the East Asian populations so far.

Conclusions

Steroid-resistant nephrotic syndrome and focal segmental glomerulosclerosis are the most common phenotypes and renal histopathological manifestations of COQ8B variant. Nonetheless, our case shows that such variant may have hidden and mild clinical manifestations at the early onset. Therefore, early diagnosis will help to identify children at the early disease stage who have opportunity to benefit from oral coenzyme Q10 supplementation.

A case report of adult-onset COQ8B nephropathy presenting focal segmental glomerulosclerosis with granular swollen podocytes

Background

Primary coenzyme Q10 (CoQ10) deficiency of genetic origin is one of a few treatable focal segmental glomerulosclerosis (FSGS). Renal morphologic evidence for COQ8B mutation and CoQ10 deficiencies of other gene mutations is assessed using electron microscopy with marked increase of abnormal-shaped mitochondria in podocytes. However, light microscopic morphologic features of deficiencies other than FSGS have not been reported.

Case presentation

A 30-year-old woman was admitted to our hospital because proteinuria was found during four consecutive medical checkups. She had no medical history or family history of proteinuria and severe renal dysfunction. The swollen podocytes were stained to the same extent as mitochondria-rich proximal tubular cells under both Masson’s trichrome and hematoxylin-eosin staining, whereas no mitochondrial abnormalities were detected under the first electron microscopic views. As proteinuria and estimated glomerular filtration rate (eGFR) deteriorated after pregnancy, we reevaluated the additional electron microscopic views and detected mitochondrial abnormalities. Genetic testing revealed COQ8B mutation (c.532C > T, p.R178W); therefore, we diagnosed COQ8B nephropathy. CoQ10 supplementation improved proteinuria and stopped eGFR reduction.

Conclusions

This is the first report of granular swollen podocytes due to mitochondrial diseases detected under light microscopy. We propose that this finding can be the clue for the diagnosis of both COQ8B nephropathy and the other CoQ10 deficiencies.

Genetic Study in Korean Pediatric Patients with Steroid-Resistant Nephrotic Syndrome or Focal Segmental Glomerulosclerosis

Steroid-resistant nephrotic syndrome (SRNS) is one of the major causes of end-stage renal disease (ESRD) in childhood and is mostly associated with focal segmental glomerulosclerosis (FSGS). More than 50 monogenic causes of SRNS or FSGS have been identified. Recently, the mutation detection rate in pediatric patients with SRNS has been reported to be approximately 30%. In this study, genotype-phenotype correlations in a cohort of 291 Korean pediatric patients with SRNS/FSGS were analyzed. The overall mutation detection rate was 43.6% (127 of 291 patients). WT1 was the most common causative gene (23.6%), followed by COQ6 (8.7%), NPHS1 (8.7%), NUP107 (7.1%), and COQ8B (6.3%). Mutations in COQ6, NUP107, and COQ8B were more frequently detected, and mutations in NPHS2 were less commonly detected in this cohort than in study cohorts from Western countries. The mutation detection rate was higher in patients with congenital onset, those who presented with proteinuria or chronic kidney disease/ESRD, and those who did not receive steroid treatment. Genetic diagnosis in patients with SRNS provides not only definitive diagnosis but also valuable information for decisions on treatment policy and prediction of prognosis. Therefore, further genotype-phenotype correlation studies are required.

ADCK4 Deficiency Destabilizes the Coenzyme Q Complex, Which Is Rescued by 2,4-Dihydroxybenzoic Acid Treatment

BACKGROUND

Mutations in ADCK4 (aarF domain containing kinase 4) generally manifest as steroid-resistant nephrotic syndrome and induce coenzyme Q₁₀ (CoQ₁₀) deficiency. However, the molecular mechanisms underlying steroid-resistant nephrotic syndrome resulting from ADCK4 mutations are not well understood, largely because the function of ADCK4 remains unknown.

METHODS

To elucidate the ADCK4's function in podocytes, we generated a podocyte-specific, Adck4-knockout mouse model and a human podocyte cell line featuring knockout of ADCK4. These knockout mice and podocytes were then treated with 2,4-dihydroxybenzoic acid (2,4-diHB), a CoQ₁₀ precursor analogue, or with a vehicle only. We also performed proteomic mass spectrometry analysis to further elucidate ADCK4's function.

RESULTS

Absence of Adck4 in mouse podocytes caused FSGS and albuminuria, recapitulating features of nephrotic syndrome caused by ADCK4 mutations. In vitro studies revealed that ADCK4-knockout podocytes had significantly reduced CoQ₁₀ concentration, respiratory chain activity, and mitochondrial potential, and subsequently displayed an increase in the number of dysmorphic mitochondria. However, treatment of 3-month-old knockout mice or ADCK4-knockout cells with 2,4-diHB prevented the development of renal dysfunction and reversed mitochondrial dysfunction in podocytes. Moreover, ADCK4 interacted with mitochondrial proteins such as COQ5, as well as cytoplasmic proteins such as myosin and heat shock proteins. Thus, ADCK4 knockout decreased the COQ complex level, but overexpression of ADCK4 in ADCK4-knockout podocytes transfected with wild-type ADCK4 rescued the COQ5 level.

CONCLUSIONS

Our study shows that ADCK4 is required for CoQ₁₀ biosynthesis and mitochondrial function in podocytes, and suggests that ADCK4 in podocytes stabilizes proteins in complex Q in podocytes. Our study also suggests a potential treatment strategy for nephrotic syndrome resulting from ADCK4 mutations.

Genetic tests in children with steroid-resistant nephrotic syndrome

Steroid-resistant nephrotic syndrome (SRNS) is a common cause of chronic kidney disease in children, and a considerable number of patients progress to end-stage renal disease. SRNS is a highly heterogeneous disorder, both clinically and genetically, and more than 50 monogenic causes of SRNS, including isolated and syndromic forms, have been identified. Recent large-cohort studies indicate that at least 30% of childhood-onset SRNS cases are genetic. The benefits of definitive molecular diagnosis by genetic testing include the avoidance of unnecessary and potentially harmful diagnostic procedures (e.g., kidney biopsy) and treatment (e.g., steroid and immunosuppressants), detection of rare and potentially treatable mutations (e.g., coenzyme Q10 biosynthesis pathway defect), prediction of prognosis (e.g., posttransplant recurrence), and providing precise genetic counseling. Furthermore, the identification of novel disease-causing genes could provide new insights into the pathogenic mechanisms of SRNS. Therefore, whenever accessible and affordable, genetic testing is recommended for all pediatric patients with SRNS, and should certainly be performed in patients with a higher probability of genetic predisposition based on genotype-phenotype correlation data. The genetic testing approach should be determined for each patient, and clinicians should, therefore, be aware of the advantages and disadvantages of methods currently available, which include Sanger sequencing, gene panel testing, and whole-exome or whole-genome sequencing. Importantly, the need for precise and thorough phenotyping by clinicians, even in the era of genomics, cannot be overemphasized. This review provides an update on recent advances in genetic studies, a suggested approach for the genetic testing of pediatric patients with SRNS.

Deletion of the Mitochondrial Complex-IV Cofactor Heme A:Farnesyltransferase Causes Focal Segmental Glomerulosclerosis and Interferon Response

Mutations in mitochondrial DNA as well as nuclear-encoded mitochondrial proteins have been reported to cause tubulointerstitial kidney diseases and focal segmental glomerulosclerosis (FSGS). Recently, genes and pathways affecting mitochondrial turnover and permeability have been implicated in adult-onset FSGS. Furthermore, dysfunctioning mitochondria may be capable of engaging intracellular innate immune-sensing pathways. To determine the impact of mitochondrial dysfunction in FSGS and secondary innate immune responses, we generated Cre/loxP transgenic mice to generate a loss-of-function deletion mutation of the complex IV assembly cofactor heme A:farnesyltransferase (COX10) restricted to cells of the developing nephrons. These mice develop severe, early-onset FSGS with innate immune activation and die prematurely with kidney failure. Mutant kidneys showed loss of glomerular and tubular epithelial function, epithelial apoptosis, and, in addition, a marked interferon response. In vitro modeling of Cox10 deletion in primary kidney epithelium compromises oxygen consumption, ATP generation, and induces oxidative stress. In addition, loss of Cox10 triggers a selective interferon response, which may be caused by the leak of mitochondrial DNA into the cytosol activating the intracellular DNA sensor, stimulator of interferon genes. This new animal model provides a mechanism to study mitochondrial dysfunction in vivo and demonstrates a direct link between mitochondrial dysfunction and intracellular innate immune response.

Clinical syndromes associated with Coenzyme Q10 deficiency

Primary Coenzyme Q deficiencies represent a group of rare conditions caused by mutations in one of the genes required in its biosynthetic pathway at the enzymatic or regulatory level. The associated clinical manifestations are highly heterogeneous and mainly affect central and peripheral nervous system, kidney, skeletal muscle and heart. Genotype–phenotype correlations are difficult to establish, mainly because of the reduced number of patients and the large variety of symptoms. In addition, mutations in the same COQ gene can cause different clinical pictures. Here, we present an updated and comprehensive review of the clinical manifestations associated with each of the pathogenic variants causing primary CoQ deficiencies.

Molecular diagnosis of coenzyme Q10 deficiency: an update

INTRODUCTION

Coenzyme Q₁₀ (CoQ) deficiency syndromes comprise a growing number of genetic disorders. While primary CoQ deficiency syndromes are rare diseases, secondary deficiencies have been related to both genetic and environmental conditions, which are the main causes of biochemical CoQ deficiency. The diagnosis is the essential first step for planning future treatment strategies, as the potential treatability of CoQ deficiency is the most critical issue for the patients. Areas covered: While the quickest and most effective tool to define a CoQ-deficient status is its biochemical determination in biological fluids or tissues, this quantification does not provide a definite diagnosis of a CoQ-deficient status nor insight about the genetic etiology of the disease. The different laboratory tests to check for CoQ deficiency are evaluated in order to choose the best diagnostic pathway for the patient. Expert commentary: New insights are being discovered about the implication of new proteins in the intricate CoQ biosynthetic pathway. These insights reinforce the idea that next generation sequencing diagnostic strategies are the unique alternative in terms of rapid and accurate molecular diagnosis of CoQ deficiency.

The Role of Glucocorticoid Receptors in Podocytes and Nephrotic Syndrome

Glucocorticoid receptor (GC), a founding member of the nuclear hormone receptor superfamily, is a glucocorticoid-activated transcription factor that regulates gene expression and controls the development and homeostasis of human podocytes. Synthetic glucocorticoids are the standard treatment regimens for proteinuria (protein in the urine) and nephrotic syndrome (NS) caused by kidney diseases. These include minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), membranous nephropathy (MN) and immunoglobulin A nephropathy (IgAN) or subsequent complications due to diabetes mellitus or HIV infection. However, unwanted side effects and steroid-resistance remain major issues for their long-term use. Furthermore, the mechanism by which glucocorticoids elicit their renoprotective activity in podocyte and glomeruli is poorly understood. Podocytes are highly differentiated epithelial cells that contribute to the integrity of kidney glomerular filtration barrier. Injury or loss of podocytes leads to proteinuria and nephrotic syndrome. Recent studies in multiple experimental models have begun to explore the mechanism of GC action in podocytes. This review will discuss progress in our understanding of the role of glucocorticoid receptor and glucocorticoids in podocyte physiology and their renoprotective activity in nephrotic syndrome.

Estimating the occurrence of primary ubiquinone deficiency by analysis of large-scale sequencing data

Primary ubiquinone (UQ) deficiency is an important subset of mitochondrial disease that is caused by mutations in UQ biosynthesis genes. To guide therapeutic efforts we sought to estimate the number of individuals who are born with pathogenic variants likely to cause this disorder. We used the NCBI ClinVar database and literature reviews to identify pathogenic genetic variants that have been shown to cause primary UQ deficiency, and used the gnomAD database of full genome or exome sequences to estimate the frequency of both homozygous and compound heterozygotes within seven genetically-defined populations. We used known population sizes to estimate the number of afflicted individuals in these populations and in the mixed population of the USA. We then performed the same analysis on predicted pathogenic loss-of-function and missense variants that we identified in gnomAD. When including only known pathogenic variants, our analysis predicts 1,665 affected individuals worldwide and 192 in the USA. Adding predicted pathogenic variants, our estimate grows to 123,789 worldwide and 1,462 in the USA. This analysis predicts that there are many undiagnosed cases of primary UQ deficiency, and that a large proportion of these will be in developing regions of the world.

Coenzyme Q10 supplementation therapy for 2 children with proteinuria renal disease and ADCK4 mutation: Case reports and literature review

RATIONALE

Mitochondrial nephropathy has a poor prognosis and often progresses to the end-stage renal disease. Renal pathology often is focal segmental glomerulosclerosis (FSGS) and does not respond to steroid therapy or immunosuppressive therapy. Some patients are benefited from the therapy of coenzyme Q10, which affect the synthesis pathway of coenzyme Q10.

PATIENT CONCERNS

Herein, we report 2 cases of children with proteinuria renal disease with ADCK4 mutation.

DIAGNOSES

Proteinuria renal disease with ADCK4 mutation.

INTERVENTIONS

Compound heterozygous mutation in ADCK4 gene were detected with next-generation sequencing and confirmed by Sanger sequencing. Both of the patients were given coenzyme Q10 supplementation therapy.

OUTCOMES

The first patient showed a decreased proteinuria after coenzyme Q10 supplementation therapy, while the other was not improved.

LESSONS

Based on the cases we reported and from the literature, recognition of ADCK4 mutation through early and accurate genetic screening could be helpful in avoiding unnecessary toxicities and in preventing complications arising in mitochondrial nephropathy.

Application of next-generation sequencing technology to diagnosis and treatment of focal segmental glomerulosclerosis

A broad range of genetic and non-genetic factors can lead to kidney injury that manifests as focal segmental glomerulosclerosis (FSGS), which can be classified into primary (idiopathic) and secondary forms. Previous genetic approaches to familial or sporadic cases of FSGS or steroid-resistant nephrotic syndrome identified causal mutations in a subset of genes. Recently, next-generation sequencing (NGS) approaches are becoming a part of a standard assessment in medical genetics. Current knowledge of the comprehensive genomic information is changing the way we think about FSGS and draws attention not only to identification of novel causal genes, but also to potential roles for combinations of mutations in multiple genes, mutations with complex inheritance, and susceptibility genes with variable penetrance carrying relatively minor but significant effects. This review provides an update on recent advances in the genetic analysis of FSGS and highlights the potential as well as the new challenges of NGS for diagnosis and mechanism-based treatment of FSGS.