Whole exome resequencing reveals recessive mutations in TRAP1 in individuals with CAKUT and VACTERL association

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 CAKUT in VACTERL association

Analysis of the Fam181 gene family during mouse development reveals distinct strain-specific expression patterns, suggesting a role in nervous system development and function

During somitogenesis differential gene expression can be observed for so-called cyclic genes, which display expression changes with a periodicity of 120 min in the mouse. In screens to identify novel cyclic genes in murine embryos, Fam181b was predicted to be an oscillating gene in the presomitic mesoderm (psm). This gene, and its closely related paralog Fam181a, belong to the thus far uncharacterized Fam181 gene family. Here we describe the expression of Fam181b and Fam181a during murine embryonic development. In addition, we confirm oscillation of Fam181b in the psm in-phase with targets of, and regulated by, Notch signaling. Fam181b expression in the psm, as well as in the lateral plate mesoderm, was found to be affected by genetic background. We show that Fam181a and b exhibit partially overlapping mRNA expression patterns, and encode for proteins containing highly-conserved motifs, which predominantly localize to the nucleus. A Fam181b loss-of-function model was generated and found to result in no obvious phenotype

Genome-wide Association Study and Meta-Analysis Identify ISL1 as Genome-wide Significant Susceptibility Gene for Bladder Exstrophy

Abstract The bladder exstrophy-epispadias complex (BEEC) represents the severe end of the uro-rectal malformation spectrum, and is thought to result from aberrant embryonic morphogenesis of the cloacal membrane and the urorectal septum. The most common form of BEEC is isolated classic bladder exstrophy (CBE). To identify susceptibility loci for CBE, we performed a genome-wide association study (GWAS) of 110 CBE patients and 1,177 controls of European origin. Here, an association was found with a region of approximately 220kb on chromosome 5q11.1. This region harbors the ISL1 (ISL LIM homeobox 1) gene. Multiple markers in this region showed evidence for association with CBE, including 84 markers with genome-wide significance. We then performed a meta-analysis using data from a previous GWAS by our group of 98 CBE patients and 526 controls of European origin. This meta-analysis also implicated the 5q11.1 locus in CBE risk. A total of 138 markers at this locus reached genome-wide significance in the meta-analysis, and the most significant marker (rs9291768) achieved a P value of 2.13 × 10−12. No other locus in the meta-analysis achieved genome-wide significance. We then performed murine expression analyses to follow up this finding. Here, Isl1 expression was detected in the genital region within the critical time frame for human CBE development. Genital regions with Isl1 expression included the peri-cloacal mesenchyme and the urorectal septum. The present study identified the first genome-wide significant locus for CBE at chromosomal region 5q11.1, and provides strong evidence for the hypothesis that ISL1 is the responsible candidate gene in this region. Author Summary The etiology of classic exstrophy of the bladder (CBE) remains unclear. The present genome-wide association study and meta-analysis identified an association between CBE and a region on chromosome 5q11.1. This region contains the gene encoding insulin gene enhancer protein, ISL-1. In this region, 138 single nucleotide polymorphisms (SNPs) reached genome-wide significance, with the SNP rs9291768 showing the lowest P value (p = 2.13 x 10−12). Our findings, as supported by expression analyses in murine models, suggest that ISL1 is a susceptibility gene for CBE

Classic Bladder Exstrophy: Frequent 22q11.21 Duplications and Definition of a 414 kb Phenocritical Region

Background: Classic bladder exstrophy (CBE) is the most common form of the bladder exstrophy and epispadias complex. Previously, we and others have identified four patients with a duplication of 22q11.21 among a total of 96 unrelated CBE patients. Methods: Here, we investigated whether this chromosomal aberration was commonly associated with CBE/bladder exstrophy and epispadias complex in an extended case-control sample. Multiplex ligation-dependent probe amplification and microarray-based analysis were used to identify 22q11.21 duplications in 244 unrelated bladder exstrophy and epispadias complex patients (including 217 CBE patients) and 665 healthy controls. Results: New duplications of variable size were identified in four CBE patients and one control. Pooling of our previous and present data (eight duplications in 313 CBE patients) yielded a combined odds ratio of 31.86 (95% confidence interval, 4.24-1407.97). Array-based sequence capture and high-throughput targeted re-sequencing established that all breakpoints resided within the low-copy repeats 22A to 22D. Comparison of the eight duplications revealed a 414 kb phenocritical region harboring 12 validated RefSeq genes. Characterization of these 12 candidate genes through whole-mount in situ hybridization of mouse embryos at embryonic day 9.5 suggested that CRKL, THAP7, and LZTR1 are CBE candidate genes. Conclusion: Our data suggest that duplication of 22q11.21 increases CBE risk and implicate a phenocritical region in disease formation. (C) 2014 Wiley Periodicals, Inc

Mutations of the SLIT2–ROBO2 pathway genes SLIT2 and SRGAP1 confer risk for congenital anomalies of the kidney and urinary tract

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

Genome-wide Association Study and Meta-Analysis Identify <i>ISL1</i> as Genome-wide Significant Susceptibility Gene for Bladder Exstrophy

<div><p>The bladder exstrophy-epispadias complex (BEEC) represents the severe end of the uro-rectal malformation spectrum, and is thought to result from aberrant embryonic morphogenesis of the cloacal membrane and the urorectal septum. The most common form of BEEC is isolated classic bladder exstrophy (CBE). To identify susceptibility loci for CBE, we performed a genome-wide association study (GWAS) of 110 CBE patients and 1,177 controls of European origin. Here, an association was found with a region of approximately 220kb on chromosome 5q11.1. This region harbors the <i>ISL1</i> (<i>ISL LIM homeobox 1</i>) gene. Multiple markers in this region showed evidence for association with CBE, including 84 markers with genome-wide significance. We then performed a meta-analysis using data from a previous GWAS by our group of 98 CBE patients and 526 controls of European origin. This meta-analysis also implicated the 5q11.1 locus in CBE risk. A total of 138 markers at this locus reached genome-wide significance in the meta-analysis, and the most significant marker (rs9291768) achieved a P value of 2.13 × 10⁻¹². No other locus in the meta-analysis achieved genome-wide significance. We then performed murine expression analyses to follow up this finding. Here, Isl1 expression was detected in the genital region within the critical time frame for human CBE development. Genital regions with <i>Isl1</i> expression included the peri-cloacal mesenchyme and the urorectal septum. The present study identified the first genome-wide significant locus for CBE at chromosomal region 5q11.1, and provides strong evidence for the hypothesis that <i>ISL1</i> is the responsible candidate gene in this region.</p></div

Most strongly associated SNP in the bladder exstrophy susceptibility locus 5q11.1.

<p>Relative risks (RRs) are given with the risk allele set as baseline. Chr, chromosome; RAF, risk allele frequency.</p><p>Most strongly associated SNP in the bladder exstrophy susceptibility locus 5q11.1.</p

Expression of <i>Isl1</i> during mouse development.

<p>Whole-mount <i>in situ</i> hybridization (ISH) for <i>Isl1</i> in wildtype mouse embryos between E9.5-E12.5 revealed strong expression in the developing genital region, including the cloaca, cloacal membrane, and emerging genital tubercle. ISH on mid-sagittal paraffin sections at later embryonic stages (E12.5-E14.5) revealed expression throughout the genital tubercle, within the peri-cloacal mesenchyme and urorectal septum. <i>Isl1</i> was also detected in the craniofacial- and spinal ganglia.</p

Genome-wide association scan in classic bladder exstrophy patients.

<p>Association of SNPs is plotted as −log₁₀(p) against chromosomal position. The y-axis shows the negative log₁₀<i>P</i> values of the logistic regression for SNPs from the meta-analysis that passed quality control. Chromosomes are shown in alternating colors along the x-axis. The genome-wide significance level is indicated by a red line.</p