Is there a dominant-negative effect in individuals with heterozygous disease-causing variants in COL4A3/COL4A4?

Alport syndrome (AS) shows a broad phenotypic spectrum ranging from isolated microscopic hematuria (MH) to end-stage kidney disease (ESKD). Monoallelic disease-causing variants in COL4A3/COL4A4 have been associated with autosomal dominant AS (ADAS) and biallelic variants with autosomal recessive AS (ARAS). The aim of this study was to analyze clinical and genetic data regarding a possible genotype-phenotype correlation in individuals with disease-causing variants in COL4A3/COL4A4. Eighty-nine individuals carrying at least one COL4A3/COL4A4 variant classified as (likely) pathogenic according to the American College of Medical Genetics guidelines and current amendments were recruited. Clinical data concerning the prevalence and age of first reported manifestation of MH, proteinuria, ESKD, and extrarenal manifestations were collected. Individuals with monoallelic non-truncating variants reported a significantly higher prevalence and earlier diagnosis of MH and proteinuria than individuals with monoallelic truncating variants. Individuals with biallelic variants were more severely affected than those with monoallelic variants. Those with biallelic truncating variants were more severely affected than those with compound heterozygous non-truncating/truncating variants or individuals with biallelic non-truncating variants. In this study an association of heterozygous non-truncating COL4A3/COL4A4 variants with a more severe phenotype in comparison to truncating variants could be shown indicating a potential dominant-negative effect as an explanation for this observation. The results for individuals with ARAS support the, still scarce, data in the literature.

Implication of transcription factor FOXD2 dysfunction in syndromic congenital anomalies of the kidney and urinary tract (CAKUT).

Congenital anomalies of the kidney and urinary tract (CAKUT) are the predominant cause for chronic kidney disease below age 30 years. Many monogenic forms have been discovered due to comprehensive genetic testing like exome sequencing. However, disease-causing variants in known disease-associated genes only explain a proportion of cases. Here, we aim to unravel underlying molecular mechanisms of syndromic CAKUT in three unrelated multiplex families with presumed autosomal recessive inheritance. Exome sequencing in the index individuals revealed three different rare homozygous variants in FOXD2, encoding a transcription factor not previously implicated in CAKUT in humans: a frameshift in the Arabic and a missense variant each in the Turkish and the Israeli family with segregation patterns consistent with autosomal recessive inheritance. CRISPR/Cas9-derived Foxd2 knockout mice presented with a bilateral dilated kidney pelvis accompanied by atrophy of the kidney papilla and mandibular, ophthalmologic, and behavioral anomalies, recapitulating the human phenotype. In a complementary approach to study pathomechanisms of FOXD2-dysfunction-mediated developmental kidney defects, we generated CRISPR/Cas9-mediated knockout of Foxd2 in ureteric bud-induced mouse metanephric mesenchyme cells. Transcriptomic analyses revealed enrichment of numerous differentially expressed genes important for kidney/urogenital development, including Pax2 and Wnt4 as well as gene expression changes indicating a shift toward a stromal cell identity. Histology of Foxd2 knockout mouse kidneys confirmed increased fibrosis. Further, genome-wide association studies suggest that FOXD2 could play a role for maintenance of podocyte integrity during adulthood. Thus, our studies help in genetic diagnostics of monogenic CAKUT and in understanding of monogenic and multifactorial kidney diseases.

Abrogation of MAP4K4 protein function causes congenital anomalies in humans and zebrafish.

We report 21 families displaying neurodevelopmental differences and multiple congenital anomalies while bearing a series of rare variants in mitogen-activated protein kinase kinase kinase kinase 4 (MAP4K4). MAP4K4 has been implicated in many signaling pathways including c-Jun N-terminal and RAS kinases and is currently under investigation as a druggable target for multiple disorders. Using several zebrafish models, we demonstrate that these human variants are either loss-of-function or dominant-negative alleles and show that decreasing Map4k4 activity causes developmental defects. Furthermore, MAP4K4 can restrain hyperactive RAS signaling in early embryonic stages. Together, our data demonstrate that MAP4K4 negatively regulates RAS signaling in the early embryo and that variants identified in affected humans abrogate its function, establishing MAP4K4 as a causal locus for individuals with syndromic neurodevelopmental differences.

Monoallelic intragenic POU3F2 variants lead to neurodevelopmental delay and hyperphagic obesity, confirming the gene's candidacy in 6q16.1 deletions.

While common obesity accounts for an increasing global health burden, its monogenic forms have taught us underlying mechanisms via more than 20 single-gene disorders. Among these, the most common mechanism is central nervous system dysregulation of food intake and satiety, often accompanied by neurodevelopmental delay (NDD) and autism spectrum disorder. In a family with syndromic obesity, we identified a monoallelic truncating variant in POU3F2 (alias BRN2) encoding a neural transcription factor, which has previously been suggested as a driver of obesity and NDD in individuals with the 6q16.1 deletion. In an international collaboration, we identified ultra-rare truncating and missense variants in another ten individuals sharing autism spectrum disorder, NDD, and adolescent-onset obesity. Affected individuals presented with low-to-normal birth weight and infantile feeding difficulties but developed insulin resistance and hyperphagia during childhood. Except for a variant leading to early truncation of the protein, identified variants showed adequate nuclear translocation but overall disturbed DNA-binding ability and promotor activation. In a cohort with common non-syndromic obesity, we independently observed a negative correlation of POU3F2 gene expression with BMI, suggesting a role beyond monogenic obesity. In summary, we propose deleterious intragenic variants of POU3F2 to cause transcriptional dysregulation associated with hyperphagic obesity of adolescent onset with variable NDD.

Implication of FOXD2 dysfunction in syndromic congenital anomalies of the kidney and urinary tract (CAKUT).

Background: Congenital anomalies of the kidney and urinary tract (CAKUT) are the predominant cause for chronic kidney disease below 30 years of age. Many monogenic forms have been discovered mainly due to comprehensive genetic testing like exome sequencing (ES). However, disease-causing variants in known disease-associated genes still only explain a proportion of cases. Aim of this study was to unravel the underlying molecular mechanism of syndromic CAKUT in two multiplex families with presumed autosomal recessive inheritance. Methods and Results: ES in the index individuals revealed two different rare homozygous variants in FOXD2, a transcription factor not previously implicated in CAKUT in humans: a frameshift in family 1 and a missense variant in family 2 with family segregation patterns consistent with autosomal-recessive inheritance. CRISPR/Cas9-derived Foxd2 knock-out (KO) mice presented with bilateral dilated renal pelvis accompanied by renal papilla atrophy while extrarenal features included mandibular, ophthalmologic, and behavioral anomalies, recapitulating the phenotype of humans with FOXD2 dysfunction. To study the pathomechanism of FOXD2-dysfunction-mediated developmental renal defects, in a complementary approach, we generated CRISPR/Cas9-mediated KO of Foxd2 in ureteric-bud-induced mouse metanephric mesenchyme cells. Transcriptomic analyses revealed enrichment of numerous differentially expressed genes important in renal/urogenital development, including Pax2 and Wnt4 as well as gene expression changes indicating a cell identity shift towards a stromal cell identity. Histology of Foxd2 KO mouse kidneys confirmed increased fibrosis. Further, GWAS data (genome-wide association studies) suggests that FOXD2 could play a role for maintenance of podocyte integrity during adulthood. Conclusions: In summary, our data implicate that FOXD2 dysfunction is a very rare cause of autosomal recessive syndromic CAKUT and suggest disturbances of the PAX2-WNT4 cell signaling axis contribute to this phenotype.

Exome sequencing in individuals with congenital anomalies of the kidney and urinary tract (CAKUT): a single-center experience.

Individuals with congenital anomalies of the kidney and urinary tract (CAKUT) show a broad spectrum of malformations. CAKUT can occur in an isolated fashion or as part of a syndromic disorder and can lead to end-stage kidney failure. A monogenic cause can be identified in ~12% of affected individuals. This study investigated a single-center CAKUT cohort analyzed by exome sequencing (ES). Emphasis was placed on the question whether diagnostic yield differs between certain CAKUT phenotypes (e.g., bilateral kidney affection, unilateral kidney affection or only urinary tract affection). 86 unrelated individuals with CAKUT were categorized according to their phenotype and analyzed by ES to identify a monogenic cause. Prioritized variants were rated according to the recommendations of the American College of Medical Genetics and Genomics and the Association for Clinical Genomic Science. Diagnostic yields of different phenotypic categories were compared. Clinical data were collected using a standardized questionnaire. In the study cohort, 7/86 individuals had a (likely) pathogenic variant in the genes PAX2, PBX1, EYA1, or SALL1. Additionally, in one individual, a 17q12 deletion syndrome (including HNF1B) was detected. 64 individuals had a kidney affection, which was bilateral in 36. All solved cases (8/86, 9%) had bilateral kidney affection (diagnostic yield in subcohort: 8/36, 22%). Although the diagnostic yield in CAKUT cohorts is low, our single-center experience argues, that, in individuals with bilateral kidney affection, monogenic burden is higher than in those with unilateral kidney or only urinary tract affection.

Renal X-inactivation in female individuals with X-linked Alport syndrome primarily determined by age.

X-linked Alport syndrome (AS) caused by hemizygous disease-causing variants in COL4A5 primarily affects males. Females with a heterozygous state show a diverse phenotypic spectrum ranging from microscopic hematuria to end-stage kidney disease (ESKD) and extrarenal manifestations. In other X-linked diseases, skewed X-inactivation leads to preferential silencing of one X-chromosome and thus can determine the phenotype in females. We aimed to show a correlation between X-inactivation in blood and urine-derived renal cells and clinical phenotype of females with a heterozygous disease-causing variant in COL4A5 compared to healthy controls. A total of 56 females with a heterozygous disease-causing COL4A5 variant and a mean age of 31.6 ± 18.3 SD years were included in this study. A total of 94% had hematuria, 62% proteinuria >200 mg/day, yet only 7% had decreased eGFR. Using human androgen receptor assay X-inactivation was examined in blood cells of all 56 individuals, in urine-derived cells of 27 of these individuals and in all healthy controls. X-inactivation did not correlate with age of first manifestation, proteinuria or eGFR neither in blood, nor in urine. The degree of X-inactivation showed a moderate association with age, especially in urine-derived cells of the patient cohort (rho = 0.403, p = 0.037). Determination of X-inactivation allelity revealed a shift of X-inactivation toward the COL4A5 variant bearing allele. This is the first study examining X-inactivation of urine-derived cells from female individuals with AS. A correlation between phenotype and X-inactivation could not be observed suspecting other genetic modifiers shaping the phenotype in female individuals with AS. The association of X-inactivation with age in urine-derived cells suggests an escape-mechanism inactivating the COL4A5 variant carrying allele in female individuals with AS.

High detection rate for disease-causing variants in a cohort of 30 Iranian pediatric steroid resistant nephrotic syndrome cases.

Background: Steroid resistant nephrotic syndrome (SRNS) represents a significant renal disease burden in childhood and adolescence. In contrast to steroid sensitive nephrotic syndrome (SSNS), renal outcomes are significantly poorer in SRNS. Over the past decade, extensive genetic heterogeneity has become evident while disease-causing variants are still only identified in 30% of cases in previously reported studies with proportion and type of variants identified differing depending on the age of onset and ethnical background of probands. A genetic diagnosis however can have implications regarding clinical management, including kidney transplantation, extrarenal disease manifestations, and, in some cases, even causal therapy. Genetic diagnostics therefore play an important role for the clinical care of SRNS affected individuals. Methodology and results: Here, we performed NPHS2 Sanger sequencing and subsequent exome sequencing in 30 consanguineous Iranian families with a child affected by SRNS with a mean age of onset of 16 months. We identified disease-causing variants and one variant of uncertain significance in 22 families (73%), including variants in NPHS1 (30%), followed by NPHS2 (20%), WT1 (7%) as well as in NUP205, COQ6, ARHGDIA, SGPL1, and NPHP1 in single cases. Eight of these variants have not previously been reported as disease-causing, including four NPHS1 variants and one variant in NPHS2, ARHGDIA, SGPL1, and NPHP1 each. Conclusion: In line with previous studies in non-Iranian subjects, we most frequently identified disease-causing variants in NPHS1 and NPHS2. While Sanger sequencing of NPHS2 can be considered as first diagnostic step in non-congenital cases, the genetic heterogeneity underlying SRNS renders next-generation sequencing based diagnostics as the most efficient genetic screening method. In accordance with the mainly autosomal recessive inheritance pattern, diagnostic yield can be significantly higher in consanguineous than in outbred populations.

The multifaceted phenotypic and genotypic spectrum of type-IV-collagen-related nephropathy-A human genetics department experience.

Disease-causing variants in COL4A3-5 are associated with type-IV-collagen-related nephropathy, a genetically and phenotypically multifaceted disorder comprising Alport syndrome (AS) and thin basement membrane nephropathy (TBMN) and autosomal, X-linked and a proposed digenic inheritance. Initial symptoms of individuals with AS are microscopic hematuria followed by proteinuria leading to kidney failure (90% on dialysis < age 40 years). In contrast, individuals with TBMN, an outdated histology-derived term, present with microscopic hematuria, only some of them develop kidney failure (>50 years of age). An early diagnosis of type-IV-collagen-related nephropathy is essential for optimized therapy and slowing of the disease. Sixty index cases, in whom exome sequencing had been performed and with disease-causing variant(s) in COL4A3-5, were evaluated concerning their clinical tentative diagnosis and their genotype. Of 60 reevaluated individuals with type-IV-collagen-related nephropathy, 72% had AS, 23% TBMN and 5% focal segmental glomerulosclerosis (FSGS) as clinical tentative diagnosis. The FSGS cases had to be re-classified as having type-IV-collagen-related nephropathy. Twelve percent of cases had AS as clinical tentative diagnosis and a monoallelic disease-causing variant in COL4A3/4 but could not be classified as autosomal dominant AS because of limited or conflicting clinical data. This study illustrates the complex clinical and genetic picture of individuals with a type IV-collagen-related nephropathy indicating the need of a refined nomenclature and the more interdisciplinary teamwork of clinicians and geneticists as the key to optimized patient care.

Disorders of histone methylation: Molecular basis and clinical syndromes.

Epigenetic modifications of DNA and histone tails are essential for gene expression regulation. They play an essential role in neurodevelopment as nervous system development is a complex process requiring a dynamic pattern of gene expression. Histone methylation is one of the vital epigenetic regulators and mostly occurs on lysine residues of histones H3 and H4. Histone methylation is catalyzed by two sets of enzymes: histone lysine methyltransferases (KMTs) and histone lysine demethylases (KDMs). KMT2 enzymes form a distinct multi-subunit complex known as COMPASS to enhance their catalytic activity and diversify their biologic functions. Several neurodevelopmental syndromes result from defects in histone methylation which can be caused by deficiencies in histone methyltransferases and demethylases, loss of the histone methyltransferase activator TASP1, or derangements in COMPASS formation. In this review article, the molecular mechanism of histone methylation is discussed followed by summarizing clinical syndromes caused by monogenic defects in histone methylation.

Oral Coenzyme Q10 supplementation leads to better preservation of kidney function in steroid-resistant nephrotic syndrome due to primary Coenzyme Q10 deficiency.

Primary Coenzyme Q10 (CoQ10) deficiency is an ultra-rare disorder caused by defects in genes involved in CoQ10 biosynthesis leading to multidrug-resistant nephrotic syndrome as the hallmark kidney manifestation. Promising early results have been reported anecdotally with oral CoQ10 supplementation. However, the long-term efficacy and optimal prescription remain to be established. In a global effort, we collected and analyzed information from 116 patients who received CoQ10 supplements for primary CoQ10 deficiency due to biallelic pathogenic variants in either the COQ2, COQ6 or COQ8B genes. Median duration of follow up on treatment was two years. The effect of treatment on proteinuria was assessed, and kidney survival was analyzed in 41 patients younger than 18 years with chronic kidney disease stage 1-4 at the start of treatment compared with that of an untreated cohort matched by genotype, age, kidney function, and proteinuria. CoQ10 supplementation was associated with a substantial and significant sustained reduction of proteinuria by 88% at 12 months. Complete remission of proteinuria was more frequently observed in COQ6 disease. CoQ10 supplementation led to significantly better preservation of kidney function (5-year kidney failure-free survival 62% vs. 19%) with an improvement in general condition and neurological manifestations. Side effects of treatment were uncommon and mild. Thus, our findings indicate that all patients diagnosed with primary CoQ10 deficiency should receive early and life-long CoQ10 supplementation to decelerate the progression of kidney disease and prevent further damage to other organs.

Suleiman-El-Hattab syndrome: a histone modification disorder caused by TASP1 deficiency.

BACKGROUND: TASP1 encodes an endopeptidase activating histone methyltransferases of the KMT2 family. Homozygous loss-of-function variants in TASP1 have recently been associated with Suleiman-El-Hattab syndrome. We report six individuals with Suleiman-El-Hattab syndrome and provide functional characterization of this novel histone modification disorder in a multi-omics approach. METHODS: Chromosomal microarray/exome sequencing in all individuals. Western blotting from fibroblasts in two individuals. RNA sequencing and proteomics from fibroblasts in one individual. Methylome analysis from blood in two individuals. Knock-out of tasp1 orthologue in zebrafish and phenotyping. RESULTS: All individuals had biallelic TASP1 loss-of-function variants and a phenotype including developmental delay, multiple congenital anomalies (including cardiovascular and posterior fossa malformations), a distinct facial appearance and happy demeanor. Western blot revealed absence of TASP1. RNA sequencing/proteomics showed HOX gene downregulation (HOXA4, HOXA7, HOXA1 and HOXB2) and dysregulation of transcription factor TFIIA. A distinct methylation profile intermediate between control and Kabuki syndrome (KMT2D) profiles could be produced. Zebrafish tasp1 knock-out revealed smaller head size and abnormal cranial cartilage formation in tasp1 crispants. CONCLUSION: This work further delineates Suleiman-El-Hattab syndrome, a recognizable neurodevelopmental syndrome. Possible downstream mechanisms of TASP1 deficiency include perturbed HOX gene expression and dysregulated TFIIA complex. Methylation pattern suggests that Suleiman-El-Hattab syndrome can be categorized into the group of histone modification disorders including Wiedemann-Steiner and Kabuki syndrome.

Connectome Analysis in an Individual with SETD1B -Related Neurodevelopmental Disorder and Epilepsy.

OBJECTIVE: Causative variants in SETD1B , encoding a lysine-specific methyltransferase, have recently been associated with a neurodevelopmental phenotype encompassing intellectual disability, autistic features, pronounced language delay, and epilepsy. It has been noted that long-term and deep phenotype data are needed to further delineate this rare condition. METHODS: In this study, we provide an in-depth clinical characterization with long-term follow-up and trio exome sequencing findings to describe one additional individual affected by SETD1B -related disorder. The diagnostic workup was complemented by a functional magnetic resonance imaging (fMRI) study. RESULTS: We report a 24-year-old male individual with an early-onset neurodevelopmental disorder with epilepsy due to the de novo missense variant c.5699A>G, p.(Tyr1900Cys) in SETD1B (NM_015048.1). He exhibited delayed speech development, autism spectrum disorder, and early-onset epilepsy with absence and generalized tonic-clonic seizures. Despite profoundly impaired communication skills, ongoing improvements regarding language production have been noted in adulthood. fMRI findings demonstrate abnormal language activation and resting-state connectivity structure. CONCLUSION: Our report expands the previously delineated phenotype of SETD1B -related disorder and provides novel insights into underlying disease mechanisms.

Exome sequencing in individuals with cardiovascular laterality defects identifies potential candidate genes.

The birth prevalence of laterality defects is about 1.1/10,000 comprising different phenotypes ranging from situs inversus totalis to heterotaxy, mostly associated with complex congenital heart defects (CHD) and situs abnormalities such as intestinal malrotation, biliary atresia, asplenia, or polysplenia. A proportion of laterality defects arise in the context of primary ciliary dyskinesia (PCD) accompanied by respiratory symptoms or infertility. In this study, exome sequencing (ES) was performed in 14 case-parent trios/quattros with clinical exclusion of PCD prior to analysis. Moreover, all cases and parents underwent detailed clinical phenotyping including physical examination, echocardiography by a skilled paediatric cardiologist and abdominal ultrasound examinations not to miss mildly affected individuals. Subsequent survey of the exome data comprised filtering for monoallelic de novo, rare biallelic, and X-linked recessive variants. In two families, rare variants of uncertain significance (VUS) in PKD1L1 and ZIC3 were identified. Both genes have been associated with laterality defects. In two of the remaining families, biallelic variants in LMBRD1 and DNAH17, respectively, were prioritized. In another family, an ultra-rare de novo variant in WDR47 was found. Extensive exome survey of 2,109 single exomes of individuals with situs inversus totalis, heterotaxy, or isolated CHD identified two individuals with novel monoallelic variants in WDR47, but no further individuals with biallelic variants in DNAH17 or LMBRD1. Overall, ES of 14 case-parent trios/quattros with cardiovascular laterality defects identified rare VUS in two families in known disease-associated genes PKD1L1 and ZIC3 and suggests DNAH17, LMBRD1, and WDR47 as potential genes involved in laterality defects.

Variation of the clinical spectrum and genotype-phenotype associations in Coenzyme Q10 deficiency associated glomerulopathy.

Primary Coenzyme Q10 deficiency is a rare mitochondriopathy with a wide spectrum of organ involvement, including steroid-resistant nephrotic syndrome mainly associated with disease-causing variants in the genes COQ2, COQ6 or COQ8B. We performed a systematic literature review, PodoNet, mitoNET, and CCGKDD registries queries and an online survey, collecting comprehensive clinical and genetic data of 251 patients spanning 173 published (47 updated) and 78 new cases. Kidney disease was first diagnosed at median age 1.0, 1.2 and 9.8 years in individuals with disease-causing variants in COQ2, COQ6 and COQ8B, respectively. Isolated kidney involvement at diagnosis occurred in 34% of COQ2, 10.8% of COQ6 and 70.7% of COQ8B variant individuals. Classic infantile multiorgan involvement comprised 22% of the COQ2 variant cohort while 47% of them developed neurological symptoms at median age 2.7 years. The association of steroid-resistant nephrotic syndrome and sensorineural hearing loss was confirmed as the distinctive phenotype of COQ6 variants, with hearing impairment manifesting at average age three years. None of the patients with COQ8B variants, but 50% of patients with COQ2 and COQ6 variants progressed to kidney failure by age five. At adult age, kidney survival was equally poor (20-25%) across all disorders. A number of sequence variants, including putative local founder mutations, had divergent clinical presentations, in terms of onset age, kidney and non-kidney manifestations and kidney survival. Milder kidney phenotype was present in those with biallelic truncating variants within the COQ8B variant cohort. Thus, significant intra- and inter-familial phenotype variability was observed, suggesting both genetic and non-genetic modifiers of disease severity.

A de novo truncating variant in CSDE1 in an adult-onset neuropsychiatric phenotype without intellectual disability.

Variants in CSDE1, a gene encoding a constrained RNA-binding protein, have recently been associated with a spectrum of neurodevelopmental conditions encompassing autism, seizures and ocular abnormalities. According to previously reported individuals, pathogenic variants in CSDE1 are typically associated with developmental delay and intellectual disability. Here, we report one individual with normal neurodevelopment and adult-onset neuropsychiatric features (i.e., acute psychosis) due to the novel de novo truncating variant c.2272C>T, p.(Gln758*) in CSDE1 (NM_001242891.1). Neuropsychological assessment confirmed deficits regarding verbal fluency, semantic memory, executive function and processing speed. Overall, our findings expand the phenotypic spectrum of CSDE1-related disorder towards the mild end.

Lifelong effect of therapy in young patients with the COL4A5 Alport missense variant p.(Gly624Asp): a prospective cohort study.

BACKGROUND: Angiotensin-converting enzyme inhibitors (ACEis) have evolved as a first-line therapy for delaying end-stage renal failure (ESRF) in Alport syndrome (AS). The present study tested the hypothesis of a superior nephroprotective potential of an early ACEi intervention, examining a cohort with the COL4A5 missense variant p.(Gly624Asp). METHODS: In this observational cohort study (NCT02378805), 114 individuals with the identical gene variant were explored for age at ESRF and life expectancy in correlation with treatment as endpoints. RESULTS: All 13 untreated hemizygous patients developed ESRF (mean age 48.9 ± 13.7 years), as did 3 very late treated hemizygotes (51.7 ± 4.2 years), with a mean life expectancy of 59.2 ± 9.6 years. All 28 earlier-treated [estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m2] hemizygous patients were still alive and still had not reached ESRF. Therapy minimized the annual loss of their GFR, similar to the annual loss in healthy individuals. Of 65 heterozygotes, 4 untreated individuals developed ESRF at an age of 53.3 ± 20.7 years. None of the treated heterozygous females developed ESRF. CONCLUSIONS: For the first time, this study shows that in AS, early therapy in individuals with missense variants might have the potential to delay renal failure for their lifetime and thus to improve life expectancy and quality of life without the need for renal replacement therapy. Some treated patients have reached their retirement age with still-functioning kidneys, whereas their untreated relatives have reached ESRF at the same or a younger age. Thus, in children with glomerular haematuria, early testing for Alport-related gene variants could lead to timely nephroprotective intervention.

There is more to it than just congenital heart defects - The phenotypic spectrum of TAB2-related syndrome.

BACKGROUND: Congenital heart defects (CHD) are the most common birth defect and disease-causing variant in TAB2 have found to be associated with isolated CHD. Recently, it became evident that pathogenic, mostly loss-of-function variants in TAB2 can also cause syndromic CHD that includes connective tissue anomalies. The number of published cases is limited posing a challenge for counseling affected patients and their relatives. METHODS: Cases in whom whole exome sequencing was executed at our institute between January 2015 and June 2021 were screened for disease-causing variants in TAB2. Additionally, a PubMed-based review of the literature was performed in December 2021 in order to give an updated clinical overview of the TAB2-associated phenotypic spectrum, including our cases. RESULTS: We identified three cases with syndromic CHD caused by different heterozygous loss-of-function variants in TAB2. In one of these cases, the variant was inherited by a healthy father. A comparison with published cases highlights that most patients were affected by structural and/or arrhythmic heart disease (about 90%) while about two third of all cases had syndromic comorbidity especially connective tissue defects and dysmorphic abnormalities. CONCLUSION: Our findings indicate a variable expressivity as well as reduced penetrance of TAB2-associated CHD. Disease-causing variants in TAB2 should be considered in cases with isolated CHD but also in syndromic CHD with connective tissue abnormalities. However, prediction of the patients' clinical outcome solely based on the variant in TAB2 is still extremely challenging.

Congenital disorders of glycosylation with defective fucosylation.

Fucosylation is essential for intercellular and intracellular recognition, cell-cell interaction, fertilization, and inflammatory processes. Only five types of congenital disorders of glycosylation (CDG) related to an impaired fucosylation have been described to date: FUT8-CDG, FCSK-CDG, POFUT1-CDG SLC35C1-CDG, and the only recently described GFUS-CDG. This review summarizes the clinical findings of all hitherto known 25 patients affected with those defects with regard to their pathophysiology and genotype. In addition, we describe five new patients with novel variants in the SLC35C1 gene. Furthermore, we discuss the efficacy of fucose therapy approaches within the different defects.

Renal and Skeletal Anomalies in a Cohort of Individuals With Clinically Presumed Hereditary Nephropathy Analyzed by Molecular Genetic Testing.

Background: Chronic kidney disease (CKD) in childhood and adolescence occurs with a median incidence of 9 per million of the age-related population. Over 70% of CKD cases under the age of 25 years can be attributed to a hereditary kidney disease. Among these are hereditary podocytopathies, ciliopathies and (monogenic) congenital anomalies of the kidney and urinary tract (CAKUT). These disease entities can present with a vast variety of extrarenal manifestations. So far, skeletal anomalies (SA) have been infrequently described as extrarenal manifestation in these entities. The aim of this study was to retrospectively investigate a cohort of individuals with hereditary podocytopathies, ciliopathies or CAKUT, in which molecular genetic testing had been performed, for the extrarenal manifestation of SA. Material and Methods: A cohort of 65 unrelated individuals with a clinically presumed hereditary podocytopathy (focal segmental glomerulosclerosis, steroid resistant nephrotic syndrome), ciliopathy (nephronophthisis, Bardet-Biedl syndrome, autosomal recessive/dominant polycystic kidney disease), or CAKUT was screened for SA. Data was acquired using a standardized questionnaire and medical reports. 57/65 (88%) of the index cases were analyzed using exome sequencing (ES). Results: 8/65 (12%) index individuals presented with a hereditary podocytopathy, ciliopathy, or CAKUT and an additional skeletal phenotype. In 5/8 families (63%), pathogenic variants in known disease-associated genes (1x BBS1, 1x MAFB, 2x PBX1, 1x SIX2) could be identified. Conclusions: This study highlights the genetic heterogeneity and clinical variability of hereditary nephropathies in respect of skeletal anomalies as extrarenal manifestation.