Background Primary hyperoxaluria type 1 (PH1) is a rare inherited metabolic disorder leading to the formation of kidney stones, nephrocalcinosis, and kidney failure. Besides, PH1 poses the risk of developing systemic oxalosis, a life-threatening condition with oxalate deposits in multiple organ systems. The rarity of the disorder combined with recent major additions to therapeutic options based on small interfering RNA (siRNA) therapeutics make a formal assessment of current practice and implementation of treatment recommendations an important asset.Methods An international questionnaire survey was conducted among medical doctors involved in the treatment of patients with chronic kidney disease. The survey included 32 questions addressing demographics, diagnostics and therapeutics, and educational needs related to the care for PH1 patients.Results 176 participants from 43 countries completed the survey, the majority of them were from Europe. The results indicate clear shortcomings in the availability of recommended diagnostics, especially with regards to plasma oxalate. Genetic testing strategies often do not include patients who may have PH1, e.g. when the underlying cause of kidney failure is unknown or in patients with nephrolithiasis or nephrocalcinosis. Treatment modalities are only partly harmonized and intensified dialysis is not fully implemented across centers. Strategies toward combination of conventional therapeutics such as hyperhydration and pyridoxine with new siRNA therapeutics depend on the treating physician's expertise. The survey identifies clear needs regarding implementation of current treatment recommendations as well as important educational gaps.Conclusion The advent of targeted treatment opportunities for PH1 comes with an increased need to provide guidance to the field. Filling the existing gaps will ensure that a growing number of patients get access to optimal care and novel life-changing therapies.

Autosomal dominant tubulointerstitial kidney disease (ADTKD) constitutes a spectrum of rare, but underdiagnosed renal disorders. ADTKD presents with a bland urinary sediment (no hematuria and little to no proteinuria), usually has no extrarenal manifestations (with the exception of HNF1B-associated disease), and results in a slowly progressive chronic kidney disease. Renal failure typically occurs in the fourth to fifth decade of life. Despite a uniform clinical picture, there is substantial interfamilial- and intrafamilial diversity in progression of CKD sometimes ranging from before the third to beyond the sixth decade of life.ADTKD shows modest genetic heterogeneity, with four main types (UMOD, MUC1, HNF1B, and REN) accounting for the vast majority of cases. However, sometimes ADTKD is used as an umbrella term for a broader number of isolated or syndromal conditions that may present with an ADTKD phenotype. The two most common ADTKD types caused by pathogenic variants in the glycoproteins uromodulin (UMOD), mucin 1 (MUC1), and the enzyme renin (REN) show striking similarities in their molecular pathophysiology and are considered toxic proteinopathies.From a spectrum of kidney disease virtually unknown to the public and to large parts of the medical community before the identification of UMOD as the first identified cause of ADTKD (then termed MCKD2) in 2002, ADTKD is increasingly recognized as a leading genetic cause of kidney disease in adults. The identification of MUC1 as the cause for the second main type has greatly stimulated research on all aspects of ADTKD and unveiled important molecular insights into its underlying pathophsiology. Our molecular knowledge on common ADTKD forms has passed the critical threshold required for developing targeted therapeutic strategies and personalized treatment approaches can be expected in the near future.

Abstract Background Pathogenic variants in the HNF1B gene cause a multi system disorder encompassing organ abnormalities—primarily affecting the kidneys and pancreas—as well as metabolic disturbances, collectively referred to as HNF1B-related disease. While maturity-onset diabetes of the young type 5 is a well-recognized manifestation, neonatal diabetes mellitus (NDM) associated with HNF1B is exceedingly rare, and has only been reported in patients harboring single nucleotide variants. Case presentation We describe two unrelated female children presenting with transient NDM caused by a complete HNF1B gene deletion. Both developed hyperglycemia within the first days of life requiring short-term insulin therapy, followed by spontaneous normalization of glycemia. However, their subsequent phenotypes diverged significantly. The first patient exhibited bilateral renal dysplasia while maintaining normal neurodevelopment. In contrast, the second patient developed later-onset cystic kidney disease, neurodevelopmental delay, and dysmorphic features, consistent with a broader 17q12 deletion syndrome spectrum. Although, in both cases, kidney abnormalities and extra-renal features (NDM, hypomagnesemia, hyperuricemia) were observed, both patients experienced a delay in diagnosis. On follow-up, serial oral glucose tolerance tests (OGTT), HbA1c assessments, and glucagon stimulation tests to date demonstrated preserved β-cell function, with the exception of hyperglycemia in 30–60 min of the extended OGTT in one patient. Conclusions These two cases represent the first report of transient NDM due to HNF1B deletion. Our findings broaden the molecular and clinical spectrum of HNF1B-related diabetes, and emphasize the importance of considering HNF1B defects in children with transient neonatal hyperglycemia.

Familial hypocalciuric hypercalcemia (FHH) is a rare genetic disorder of calcium regulation. FHH type 3 (FHH3), caused by pathogenic variants in AP2S1, may present with clinically significant complications. Data on the treatment of this rare disorder is limited. CASE DESCRIPTION: We report an 11-year-old girl with a de novo heterozygous pathogenic variant in AP2S1 (NM_004069.6): c.44G>T p.(Arg15Leu). At the age of seven, our patient presented with hypercalcemia, hypocalciuria, and elevated parathyroid hormone (PTH), which were accompanied by low bone mineral density and persistent neurodevelopmental difficulties. Primary hyperparathyroidism and causative variants in the CASR gene were excluded, and cinacalcet was initiated. After a dose titration and vitamin D3 dose adjustments, a normalization of serum calcium and PTH was achieved, and symptoms improved substantially, although lumbar bone mineral density declined further, and neurological symptoms remained. CONCLUSIONS: This case demonstrates cinacalcet as an effective and well-tolerated therapy in FHH3, with unresolved questions regarding skeletal and neurocognitive outcomes.

Introduction The molecular diagnosis of autosomal dominant tubulointerstitial kidney disease due to MUC1 variants (ADTKD-MUC1) using high-throughput (short-read) sequencing methods remains challenging due to the presence of a coding long variable-number tandem repeat (VNTR) region wherein most known pathogenic variants are located. Methods Here, we used targeted amplicon long-read sequencing to study the MUC1 VNTR in a retrospective cohort study of 78 individuals. Using a bioinformatic pipeline including newly developed specialized software, VNTRtools, we reconstructed patient-specific complete VNTR haplotypes, generated a synthetic VNTR reference, performed long-read realignment to this reference, and finally performed variant calling. Results VNTRtools proved efficient, requiring seconds or minutes per sample to accurately identify all pathogenic MUC1 frameshift variants in positive controls, including atypical variants. Ten new diagnoses of ADTKD-MUC1 were made. Furthermore, we report a confirmed de novo case of ADTKD-MUC1 in a 32-year-old patient. We were able to structurally resolve and phase the interindividually highly variable VNTRs in most probands, enabling the high-confidence detection of pathogenic frameshift variants in 24 individuals. We also detected 18 previously unreported VNTR repeat unit types, demonstrating the highly polymorphic nature of MUC1’s VNTR. Conclusions We propose a combined approach in which short-read VNTR analysis using the published alignment-free bioinformatic tools is used as a first-line test, followed by targeted long-read sequencing with VNTRtools analysis for confirmatory testing and in-depth VNTR characterization. This combined approach will lead to a higher diagnostic confidence in ADTKD-MUC1—especially in sporadic cases. Complete VNTR haplotype information will likely enable a better genetic understanding of this currently underdiagnosed disorder and may become relevant for future therapeutic approaches like targeted silencing of the pathogenic MUC1 allele.

INTRODUCTION:Thrombotic microangiopathy (TMA) is characterized by the classical triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Complement inhibition with eculizumab is highly efficacious in TMA secondary to complement dysregulation. However, a growing number of eculizumab-nonresponsive TMAs are reported. Recently, a syndromic form of TMA due to recessive variants in RNA exosome components (EXOSC3 and EXOSC5) has been identified. The underlying pathogenesis remains unclear. METHODS:We identified 34 children across Europe with pontocerebellar hypoplasia 1b (PCH1b) due to EXOSC3 rare variants and reviewed their clinical history for signs of TMA. To further examine the pathogenesis, a tamoxifen-inducible whole-body Exosc3 conditional knockout mouse model (Exosc3KO) was used. RESULTS:Thirteen (eight male, five female) cases of EXOSC3-TMA were identified. In the United Kingdom, the incidence of EXOSC3-TMA was 0.004/million/year. Three children received long-term eculizumab therapy: one child failed to respond and two relapsed on treatment. Exosc3KO demonstrated cell-cycle arrest and apoptosis resulting in death in a median of eight days, with sequelae noted in actively dividing cells in the bone marrow and large intestine. In this timeframe, no kidney pathology was identified. CONCLUSIONS:EXOSC3-TMA is a severe, early-onset, C5 inhibitor-resistant TMA. EXOSC3-TMA should be considered in eculizumab-resistant pediatric TMA, particularly in the context of neurodevelopmental disease.

Introduction: Variants in the Ras-related GTPase D (RRAGD) gene have been associated with autosomal dominant kidney hypomagnesemia (ADKH) characterized by hypokalemia, nephrocalcinosis, and dilated cardiomyopathy (DCM). RRAGD, which encodes for the RagD protein, is involved in the activation of the mechanistic target of rapamycin complex 1 (mTORC1). Owing to the limited characterization of patients’ phenotypes, the understanding of RRAGD-associated ADKH (ADKH-RRAGD) remains incomplete. Consequently, available treatment strategies are primarily symptomatic and insufficient. Methods: In the present case series, 13 new patients and 3 novel RRAGD variants, that is, p.(Ser77Phe), p.(Thr91Ile), and p.(Ile100Arg), are described. To assess the pathogenicity of the novel variants, an in vitro assay of mTORC1 activity was performed. In addition, the clinical response to diuretics (furosemide and thiazide, n = 4) and Na+-glucose cotransporter 2 (SGLT2) inhibitor, dapagliflozin (n = 6) was evaluated in patients carrying the RRAGD p.(Thr97Pro) variant during routine. Results: The patients presented with kidney tubulopathies, including hypomagnesemia, hypercalciuria, and nephrocalcinosis. Five patients also exhibited DCM. In vitro assays demonstrated constitutive activation of noncanonical mTORC1 signaling caused by the p.(Ser77Phe) and p.(Ile100Arg) variants. Clinically, patients remained sensitive to diuretic challenges, whereas dapagliflozin treatment increased serum magnesium (Mg2+) levels by 0.04 mM but exacerbated hypokalemia. Conclusion: To date, 37 patients with ADKH-RRAGD have been identified. Kidney tubulopathy is the most prominent feature within the phenotypic spectrum of ADKH-RRAGD. Molecularly, constitutive activation of noncanonical mTORC1 is present in most RRAGD variants. From a therapeutic perspective, dapagliflozin may increase serum Mg2+ levels in patients with RRAGD variants.

BACKGROUND:Dysfunction of δ-aminolevulinic acid dehydratase (ALAD), the second enzyme involved in heme biosynthesis, leads to two pathologies: genetic and acquired. The genetic form is an ultrarare, severe childhood-onset disease inherited in an autosomal recessive manner, whereas the acquired form usually affects adults due to enzyme inhibition by specific chemicals. AIMS AND PATIENT COHORT:This study reports the molecular characterization of three pediatric patients with genetic ALAD deficiency porphyria (ADP), including two siblings, and five adults who exhibited features suggestive of heavy metal poisoning. Furthermore, using an innovative mouse liver model, we performed in vivo functional analysis of the pathogenic variants and lead susceptibility alleles identified in the ALAD gene. RESULTS:Siblings (one female) were found to carry the c440_441delinsTT (p.Arg147Leu) variant in homozygosis. However, the vector expression system confirmed a pathogenic role only for the c.440C > T substitution. The third patient exhibited compound heterozygosity, with a c.839G > A (p.Gly280Glu) dominant variant and a hypomorphic c.724G > A (p.Val242Ile) allele. The rs1805313 and rs8177800 common intron variants were most prevalent in patients with acquired ADP. However, increased ALAD activity for the rs1139488 synonymous variant and a hexameric ALAD conformation for the rs1800435 missense variant have been established. CONCLUSION:These findings underscore the molecular heterogeneity of the ALAD gene and present the first reported case of ADP in a female patient.

"En bloc" inheritance of point mutations in adjacent genes has rarely been described. We have previously reported a family with severe, mostly early-lethal Joubert syndrome (JBTS) with early-onset severe retinal dystrophy (EOSRD) and polycystic kidney disease (PKD), which at that time had been attributed to a homozygous pathogenic missense variant, p.Arg106Pro (c.317G>C), in the ciliary POC1B gene. Because this and other POC1B variants were, in subsequent studies, only reported in patients with non-syndromic childhood or early-adult-onset macular dystrophy, we have now reassessed our index patient by long-read high-fidelity (HiFi) whole-genome sequencing (LR-WGS). We identified a homozygous deep-intronic variant, c.2818-657T>G, in CEP290, a JBTS/Meckel syndrome-associated gene on chromosome 12q21, only 1.28 Mb from the N terminus of POC1B. cDNA analysis revealed aberrant splicing with the frame-shifting inclusion of 37 bp from CEP290 intron 25, predicting the loss of CEP290 function. EOSRD and PKD can fully be ascribed to this CEP290 variant, whose effect outshines the "background" non-syndromic POC1B retinopathy and co-segregates with the severe syndromic phenotype. Our novel findings in this family no longer justify POC1B as a JBTS gene. This co-inheritance of two ciliopathies, with the clinically decisive variant hidden deep in an intron, exemplifies the importance of WGS for achieving the complete diagnosis in challenging cases.

Nephrocalcinosis (NC) is strongly related to nephrolithiasis (NL). Patients with NL and NC have an elevated risk of chronic kidney disease (CKD). The causes of NL and NC are environmental and genetic. Although monogenic causes of NL/NC are uncommon, they represent a considerable disease burden. This study aimed to determine the diagnostic yield of genetic analysis in children and adults with NL/NC and the clinical characteristics of the patients with a positive result. A retrospective chart review of children and adults with NL/NC was conducted. Inclusion criteria were the presence of NL/NC on diagnostic imaging and performed genetic analysis between 2020 and 2023. Use of the genetic analysis, i.e. NL/NC panel was based on clinical background and suspicion for genetic disease. 22 participants were included in the study, 14 adults (ADL), and 8 children (CHL). The most common clinical feature in both groups was hypercalciuria as well as hypocitraturia. CKD was present in 50% of patients in the ADL group and 37% in the CHL group. Low serum bicarbonate was found in 29% of participants in the ADL group and 25% in the CHL group. There was no significant difference in analyzed clinical features between the groups (all P > 0.05). Overall, in 9 (41%) of participants, the result of genetic analysis was positive. The most common cause of the NL/NC in the ADL group was primary distal renal tubular acidosis. Familial hypomagnesemia with hypercalciuria and nephrocalcinosis was the most common cause of NL/NC in the CHL group. Infantile hypercalcemia 1 is the second most common cause of NL/NC in the ADL group. In the CHL group, one case of infantile hypercalcemia 1 was identified as a cause of NL/NC, as well as one case of Bartter syndrome. One case of Dent disease was recognized as a cause of NL/NC in the ADL group. This study shows that up to 50% of patients may have a positive result of genetic analysis regarding NL/NC causes. Finding the possible explanatory genetic variant in these patients is of great importance for the management of the NL/NC patient. Therefore, targeted genetic testing is a promising aid regardless of the patient's age.

Cosmc, encoded by the X-linked C1GALT1C1, is a molecular chaperone in the endoplasmic reticulum and a master regulator of O-glycosylation of mammalian glycoproteins. Recently, we described a germline mutation in C1GALT1C1 in two male patients, giving rise to a congenital disorder of glycosylation-COSMC-CDG. Here, we have identified a female patient with a de novo mosaic variant in C1GALT1C1 (c.202C>T, p.Arg68*), which results in a truncated and nonfunctional form of Cosmc (Cosmc-R68). The patient is mosaic, as ~27% of her buccal cells carry the mutation. The patient is now a 5-year old who presented with nonimmune hydrops fetalis. As Cosmc is essential for the generation of normal O-glycans through regulating T-synthase activity, thereby enabling the formation of the universal Core 1 O-glycan Galβ1-3GalNAcα1-Ser/Thr (T-antigen), the loss of Cosmc leads to the expression of the unusual precursor O-glycan termed Tn-antigen (CD175) (GalNAcα1-Ser/Thr). Owing to the mutational mosaicism, only a significant minority of cells would exhibit abnormal O-glycosylation. Analysis of red blood cells (RBCs), leukocytes, and serum from this patient indicated reduced expression of Cosmc and T-synthase proteins and lower T-synthase activity. Consistent with these findings, we observed reduced normal O-glycans in serum glycoproteins and RBCs from the patient, along with elevated expression of the Tn-antigen in serum glycoproteins compared to controls. This case represents the first description of a true mosaic loss-of-function variant in C1GALT1C1, that is, one that occurred postzygotically during embryogenesis, and raises interesting questions about the role of O-glycosylation during fetal development and its consequences on the clinical presentation.

In genetic disease, an accurate expression landscape of disease genes and faithful animal models can facilitate genetic diagnoses and therapeutic advances respectively. Previously, we found that variants in NOS1AP, the gene that encodes nitric oxide synthase 1 adaptor protein, cause monogenic nephrotic syndrome. Here, we determine that an intergenic splice product of NOS1AP/Nos1ap and neighboring C1orf226/Gm7694, which prevents NOS1AP from binding to nitric oxide synthase 1, is the predominant isoform in mammalian kidney transcriptional and proteomic data. Gm7694-/- mice, whose allele exclusively disrupts the intergenic product, develop nephrotic syndrome phenotypes. In two male human subjects with nephrotic syndrome, we identify causative NOS1AP splice variants, including one predicted to abrogate intergenic splicing but initially misclassified as benign based on the canonical transcript. Finally, by modifying genetic background, we generate a faithful mouse model of NOS1AP-associated monogenic nephrotic syndrome that responds to anti-proteinuric treatment.

Introduction: Newborn screening (NBS) programs for a defined set of eligible diseases have been enormously successful, but genomic NBS allowing for detection of additional treatable disorders has not been broadly implemented. All 3 types of primary hyperoxaluria (PH1-3) are rare autosomal recessive diseases caused by distinct defects of glyoxylate metabolism that are diagnosed genetically with certainty. Early diagnosis and treatment are mandatory to avoid renal failure or sequalae associated with persistent hyperoxaluria. Methods: This prospective pilot study was undertaken within the framework of the German NBS. DNA samples extracted from dried blood spot cards were screened by multiplex polymerase chain reaction (PCR) for the 2 most prevalent variants: AGXT c.508G>A (PH1) and HOGA1 c.700 + 5G>T (PH3). Heterozygous AGXT/HOGA1 carriers received repeated spot urine analyses and, in case of persistent hyperoxaluria, complete Sanger sequencing of AGXT and HOGA1 genes, respectively. Results: Between March 15, 2022 and June 30, 2023, additional screening for PH1 and PH3 was performed in 77,199 out of 222,638 newborns included in the regular NBS program. No homozygous individuals, but 274 potential carriers for the AGXT mistargeting and 287 potential carriers for the HOGA1 splice variant were identified. Further workup revealed 2 already symptomatic compound heterozygous infants, 1 with PH1 (genotype c.508G>A; c.33delC) and 1 with PH3 (genotype: c.700 + 5G>T; c.134C>G). A second symptomatic patient with PH1 (father of an identified carrier; genotype: c.508G>A; c.508G>A) was uncovered via family history. Conclusion: This pilot study demonstrates the efficacy of a genomic neonatal screening program for PH even in relatively small cohorts.

Nephrocalcinosis is characterised by the deposition of calcium oxalate or calcium phosphate in the tubulointerstitial regions of the kidney. Rarely, disturbances in phosphate homeostasis in the course of hyperphosphataemic familial tumoural calcinosis can be the cause of nephrocalcinosis. The main symptoms of this condition include ectopic calcifications, hyperostosis, and dental abnormalities. In this article, we present the clinical and genetic description of a case involving a 36-year-old woman in whom nephrocalcinosis was incidentally discovered and subsequently led to the diagnosis of hyperphosphataemic familial tumoural calcinosis. In the course of the molecular diagnostic process, whole-exome short-read sequencing detected a heterozygous in-frame deletion (c.1093_1095del; p.Gly365del) in the GALNT3 gene, while long-read single-molecule real-time sequencing identified a complex indel (c.1382_1388delins814) in GALNT3 exon 7. To the authors’ knowledge, this is the first described case of a patient with this specific mutation.

We aimed to develop a tool for predicting HNF1B mutations in children with congenital abnormalities of the kidneys and urinary tract (CAKUT). The clinical and laboratory data from 234 children and young adults with known HNF1B mutation status were collected and analyzed retrospectively. All subjects were randomly divided into a training (70

EDITORIAL article Front. Pediatr., 10 April 2024Sec. Pediatric Nephrology Volume 12 - 2024 | https://doi.org/10.3389/fped.2024.1401593

Introduction: In pregnancy -related atypical hemolytic uremic syndrome (p-aHUS), transferring recommendations for treatment decisions from nonpregnant cohorts with thrombotic microangiopathy (TMA) is diff i cult. Although potential causes of p-aHUS may be unrelated to inherent complement defects, peripartal complications such as postpartum hemorrhage (PPH) or (pre)eclampsia or Hemolysis, Elevated Liver enzymes and Low Platelets (HELLP) syndrome may be unrecognized drivers of complement activation. Methods: To evaluate diagnostic and therapeutic decisions in the practical real -life setting, we conducted an analysis of a cohort of 40 patients from 3 German academic hospitals with a diagnosis of p-aHUS, strati fi ed by the presence ( n = 25) or absence ( n = 15) of PPH. Results: Histological signs of TMA were observed in 84.2% of all patients (100% vs. 72.7% in patients without or with PPH, respectively). Patients without PPH had a higher likelihood (20% vs. 0%) of pathogenic genetic abnormalities in the complement system although notably less than in other published cohorts. Four of 5 patients with observed renal cortical necrosis (RCN) after PPH received complement inhibition and experienced partially recovered kidney function. Patients on complement inhibition with or without PPH had an increased need for kidney replacement therapy (KRT) and plasma exchange (PEX). Because renal recovery was comparable among all patients treated with complement inhibition, a potential bene fi cial effect in this group of pregnancy -associated TMAs and p-aHUS is presumed. Conclusion: Based on our fi ndings, we suggest a pragmatic approach toward limited and short-term anticomplement therapy for patients with a clinical diagnosis of p-aHUS, which should be stopped once causes of TMA other than genetic complement abnormalities emerge.

Hepatocytes synthesize a vast number of glycoproteins found in their membranes and secretions, many of which contain O-glycans linked to Ser/Thr residues. As the functions and distribution of O-glycans on hepatocyte-derived membrane glycoproteins and blood glycoproteins are not well understood, we generated mice with a targeted deletion of Cosmc (C1Galt1c1) in hepatocytes. Liver glycoproteins in WT mice express typical sialylated core 1 O-glycans (T antigen/CD176) (Galβ1-3GalNAcα1-O-Ser/Thr), whereas the Cosmc knockout hepatocytes (HEP-Cosmc-KO) lack extended O-glycans and express the Tn antigen (CD175) (GalNAcα1-O-Ser/Thr). Tn-containing glycoproteins occur in the sera of HEP-Cosmc-KO mice but not in WT mice. The LDL-receptor (LDLR), a well-studied O-glycosylated glycoprotein in hepatocytes, behaves as a ∼145kD glycoprotein in WT liver lysates, whereas it is reduced to ∼120 kDa in lysates from HEP-Cosmc-KO mice. Interestingly, the expression of the LDLR, as well as HMG-CoA reductase, which is typically altered in response to dysregulated cholesterol metabolism, are similar between WT and HEP-Cosmc-KO mice, indicating no significant effect by Cosmc deletion on either LDLR stability or cholesterol metabolism. Consistent with this, we observed no detectable phenotype in the HEP-Cosmc-KO mice regarding development, appearance or aging compared to WT. These results provide surprising, novel information about the pathway of O-glycosylation in the liver.