Congenital anomalies of the kidney and urinary tract (CAKUT) cover a wide range of structural malformations that result from defects in the morphogenesis of the kidney and/or urinary tract. These ...anomalies account for about 40–50 % of children with chronic kidney disease worldwide. Knowledge from genetically modified mouse models suggests that single gene mutations in renal developmental genes may lead to CAKUT in humans. However, until recently, only a handful of CAKUT-causing genes were reported, most of them in familial syndromic cases. Recent findings suggest that CAKUT may arise from mutations in a multitude of different single gene causes. We focus here on single-gene causes of CAKUT and their developmental origin. Currently, more than 20 monogenic CAKUT-causing genes have been identified. High-throughput sequencing techniques make it likely that additional CAKUT-causing genes will be identified in the near future.
Congenital anomalies of the kidney and urinary tract (CAKUT) account for approximately half of children with chronic kidney disease. CAKUT can be caused by monogenic mutations; however, data are ...lacking on their frequency. Genetic diagnosis has been hampered by genetic heterogeneity and lack of genotype–phenotype correlation. To determine the percentage of cases with CAKUT that can be explained by mutations in known CAKUT genes, we analyzed the coding exons of the 17 known dominant CAKUT-causing genes in a cohort of 749 individuals from 650 families with CAKUT. The most common phenotypes in this CAKUT cohort were vesicoureteral reflux in 288 patients, renal hypodysplasia in 120 patients, and unilateral renal agenesis in 90 patients. We identified 37 different heterozygous mutations (33 novel) in 12 of the 17 known genes in 47 patients from 41 of the 650 families (6.3%). These mutations include (number of families): BMP7 (1), CDC5L (1), CHD1L (5), EYA1 (3), GATA3 (2), HNF1B (6), PAX2 (5), RET (3), ROBO2 (4), SALL1 (9), SIX2 (1), and SIX5 (1). Furthermore, several mutations previously reported to be disease-causing are most likely benign variants. Thus, in a large cohort over 6% of families with isolated CAKUT are caused by a mutation in 12 of 17 dominant CAKUT genes. Our report represents one of the most in-depth diagnostic studies of monogenic causes of isolated CAKUT in children.
The triad of a presacral mass, sacral agenesis and an anorectal anomaly constitutes the rare Currarino syndrome (CS), which is caused by dorsal-ventral patterning defects during embryonic ...development. The major causative CS gene is MNX1, encoding a homeobox protein.
In the majority of patients, CS occurs as an autosomal dominant trait; however, a female predominance observed, implies that CS may underlie an additional mode(s) of inheritance. Often, the diagnosis of CS is established solely by clinical findings, impacting a detailed analysis of the disease. Our combined data, evaluating more than 60 studies reporting patients with CS-associated mutations, revealed a slightly higher incidence rate in females with a female-to-male ratio of 1.39:1. Overall, MNX1 mutation analysis was successful in only 57.4% of all CS patients investigated, with no mutation detected in 7.7% of the familial and 68% of the sporadic patients. Our studies failed to detect the presence of an expressed MNX1 isoform that might explain at least some of these mutation-negative cases.
Aside from MNX1, other genes or regulatory regions may contribute to CS and we discuss several cytogenetic studies and whole-exome sequencing data that have implicated further loci/genes in its etiology.
Congenital anomalies of the kidney and urinary tract (CAKUT) account for 40–50 % of chronic kidney disease that manifests in the first two decades of life. Thus far, 31 monogenic causes of isolated ...CAKUT have been described, explaining ~12 % of cases. To identify additional CAKUT-causing genes, we performed whole-exome sequencing followed by a genetic burden analysis in 26 genetically unsolved families with CAKUT. We identified two heterozygous mutations in
SRGAP1
in 2 unrelated families. SRGAP1 is a small GTPase-activating protein in the SLIT2–ROBO2 signaling pathway, which is essential for development of the metanephric kidney. We then examined the pathway-derived candidate gene
SLIT2
for mutations in cohort of 749 individuals with CAKUT and we identified 3 unrelated individuals with heterozygous mutations. The clinical phenotypes of individuals with mutations in
SLIT2
or
SRGAP1
were cystic dysplastic kidneys, unilateral renal agenesis, and duplicated collecting system. We show that
SRGAP1
is expressed in early mouse nephrogenic mesenchyme and that it is coexpressed with
ROBO2
in SIX2-positive nephron progenitor cells of the cap mesenchyme in developing rat kidney. We demonstrate that the newly identified mutations in
SRGAP1
lead to an augmented inhibition of RAC1 in cultured human embryonic kidney cells and that the
SLIT2
mutations compromise the ability of the SLIT2 ligand to inhibit cell migration. Thus, we report on two novel candidate genes for causing monogenic isolated CAKUT in humans.
The psychosocial impact of living with autosomal dominant polycystic kidney disease (ADPKD) is poorly understood. In this study, we assessed the overall quality of life (QOL), mood, perceived social ...support and psychosocial risk of having a diagnosis of ADPKD in a patient cohort from a major UK nephrology centre serving a large catchment population.
A postal questionnaire was sent to 349 patients registered at the Sheffield Kidney Institute with chronic kidney disease but not on renal replacement therapy (RRT). The questionnaire incorporated three validated forms: kidney disease quality-of-life short form (KDQOL SF1.3) to assess QOL; nine-item patient health questionnaire (PHQ9) to screen for depression; multidimensional scale of perceived social support (MSPSS) to evaluate perceived social support; as well as a novel genetic psychosocial risk instrument (GPRI-ADPKD) designed to study the specific psychosocial impact of coping with a diagnosis of ADPKD.
The overall response rate was 53%. Patients with a lower estimated glomerular filtration rate (<30 mL/min) or larger kidneys (mean length on ultrasound ≥17 cm) reported reduced QOL and increased psychosocial risk. Clinically significant depression was reported in 22% and 62% felt guilty about passing ADPKD on to their children. In multivariate analysis, female gender was associated with overall poorer psychosocial well-being, whereas increasing age, lower kidney function, larger kidneys and loss of a first degree relative from ADPKD were additional risk factors for QOL, depression or psychosocial risk, respectively.
Our results reveal a significantly poorer QOL and increasing psychosocial risk with markers of disease progression in patients, particularly women, with ADPKD prior to starting RRT. The future management strategy of ADPKD should address these issues and provide for better individual and family support throughout the patient journey.
Congenital anomalies of the kidney and urinary tract (CAKUT) account for approximately 40% of children with ESRD in the United States. Hitherto, mutations in 23 genes have been described as causing ...autosomal dominant isolated CAKUT in humans. However, >90% of cases of isolated CAKUT still remain without a molecular diagnosis. Here, we hypothesized that genes mutated in recessive mouse models with the specific CAKUT phenotype of unilateral renal agenesis may also be mutated in humans with isolated CAKUT. We applied next-generation sequencing technology for targeted exon sequencing of 12 recessive murine candidate genes in 574 individuals with isolated CAKUT from 590 families. In 15 of 590 families, we identified recessive mutations in the genes FRAS1, FREM2, GRIP1, FREM1, ITGA8, and GREM1, all of which function in the interaction of the ureteric bud and the metanephric mesenchyme. We show that isolated CAKUT may be caused partially by mutations in recessive genes. Our results also indicate that biallelic missense mutations in the Fraser/MOTA/BNAR spectrum genes cause isolated CAKUT, whereas truncating mutations are found in the multiorgan form of Fraser syndrome. The newly identified recessive biallelic mutations in these six genes represent the molecular cause of isolated CAKUT in 2.5% of the 590 affected families in this study.
is thought to play an important role in cytoskeletal modification and development of the early nervous system. Previously, single-nucleotide variants (SNVs) or copy number variations (CNVs) in
have ...been associated with the neurodevelopmental disorder Stocco dos Santos syndrome, but not with congenital anomalies of the urinary tract and the visceral or the cardiovascular system.
Here, exome sequencing and CNV analyses besides expression studies in zebrafish and mouse and
(KD) experiments using a splice blocking morpholino in zebrafish were performed to study the role of
during embryonic development.
In this study, we identified putative disease-causing SNVs and CNVs in
in six individuals from four families with congenital anomalies of the urinary tract and the anorectal, cardiovascular and central nervous systems (CNS). Embryonic mouse and zebrafish expression studies showed
expression in the upper and lower urinary tract, the developing cloaca, the heart and the cerebral CNS. KD studies in zebrafish larvae revealed pronephric cysts, anomalies of the cloaca and the heart, decreased eye-to-head ratio and higher mortality compared with controls. These phenotypes could be rescued by co-injection of human wild-type
mRNA and morpholino.
The identified SNVs and CNVs in affected individuals with congenital anomalies of the urinary tract, the anorectal, the cardiovascular and the central nervous systems, and subsequent embryonic mouse and zebrafish studies suggest
as a developmental gene for different organ systems.
To investigate the effect of PLXNA1 variants on the phenotype of patients with autosomal dominant and recessive inheritance patterns and to functionally characterize the zebrafish homologs plxna1a ...and plxna1b during development.
We assembled ten patients from seven families with biallelic or de novo PLXNA1 variants. We describe genotype-phenotype correlations, investigated the variants by structural modeling, and used Morpholino knockdown experiments in zebrafish to characterize the embryonic role of plxna1a and plxna1b.
Shared phenotypic features among patients include global developmental delay (9/10), brain anomalies (6/10), and eye anomalies (7/10). Notably, seizures were predominantly reported in patients with monoallelic variants. Structural modeling of missense variants in PLXNA1 suggests distortion in the native protein. Our zebrafish studies enforce an embryonic role of plxna1a and plxna1b in the development of the central nervous system and the eye.
We propose that different biallelic and monoallelic variants in PLXNA1 result in a novel neurodevelopmental syndrome mainly comprising developmental delay, brain, and eye anomalies. We hypothesize that biallelic variants in the extracellular Plexin-A1 domains lead to impaired dimerization or lack of receptor molecules, whereas monoallelic variants in the intracellular Plexin-A1 domains might impair downstream signaling through a dominant-negative effect.
Congenital abnormalities of the kidney and urinary tract (CAKUT) account for approximately half of children with chronic kidney disease and they are the most frequent cause of end-stage renal disease ...in children in the US. However, its genetic etiology remains mostly elusive. VACTERL association is a rare disorder that involves congenital abnormalities in multiple organs including the kidney and urinary tract in up to 60% of the cases. By homozygosity mapping and whole-exome resequencing combined with high-throughput mutation analysis by array-based multiplex PCR and next-generation sequencing, we identified recessive mutations in the gene TNF receptor–associated protein 1 (TRAP1) in two families with isolated CAKUT and three families with VACTERL association. TRAP1 is a heat-shock protein 90–related mitochondrial chaperone possibly involved in antiapoptotic and endoplasmic reticulum stress signaling. Trap1 is expressed in renal epithelia of developing mouse kidney E13.5 and in the kidney of adult rats, most prominently in proximal tubules and in thick medullary ascending limbs of Henle’s loop. Thus, we identified mutations in TRAP1 as highly likely causing CAKUT or VACTERL association with CAKUT.
Anorectal malformations (ARM) are rare abnormalities that occur in approximately 1 in 3000 live births with around 40% of patients presenting with isolated forms. Multiple familial cases reported, ...suggest underlying genetic factors that remain largely unknown. The recurrence in relatives is considered rare, however transmission rates of ARM by affected parents have never been determined before. The inheritance pattern of ARM was investigated in our database of patients with isolated ARM.
Within our cohort of 327 patients with isolated ARM we identified eight adult patients from eight families who had in total 16 children with their healthy spouse. Of these ten had ARM, resulting in a recurrence risk of approximately one in two live births (10 of 16; 62%). From 226 families with 459 siblings we found two affected siblings in five families. Hence, the recurrence risk of ARM among siblings is approximately one in 92 live births (5 of 459; 1.0%).
Comparing the observed recurrence risk in our cohort with the prevalence in the general population, we see a 1500-fold increase in recurrence risk for offspring and a 32-fold increase if a sibling is affected. The recurrence risk of approximately 62% indicates an autosomal dominant mode of inheritance. Reliable figures on recurrence of ARM are becoming increasingly important since improved surgical techniques are able to maintain sexual function resulting in more offspring of patients with ARM. These data allow more precise counseling of families with ARM and support the need for genetic studies.
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