The acronym VATER/VACTERL association describes the combination of at least three of the following congenital anomalies: vertebral defects (V), anorectal malformations (A), cardiac defects (C), tracheoesophageal fistula with or without esophageal atresia (TE), renal malformations (R), and limb defects (L). We aimed to identify highly penetrant de novo copy number variations (CNVs) that contribute to VATER/VACTERL association. Array-based molecular karyotyping was performed in a cohort of 41 patients with VATER/VACTERL association and 6 patients with VATER/VACTERL-like phenotype including all of the patients' parents. Three de novo CNVs were identified involving chromosomal regions 1q41, 2q37.3, and 8q24.3 comprising one (SPATA17), two (CAPN10, GPR35), and three (EPPK1, PLEC, PARP10) genes, respectively. Pre-existing data from the literature prompted us to choose GPR35 and EPPK1 for mouse expression studies. Based on these studies, we prioritized GPR35 for sequencing analysis in an extended cohort of 192 patients with VATER/VACTERL association and VATER/VACTERL-like phenotype. Although no disease-causing mutation was identified, our mouse expression studies suggest GPR35 to be involved in the development of the VATER/VACTERL phenotype. Follow-up of GPR35 and the other genes comprising the identified duplications is warranted.
VATER/VACTERL association; CNV analysis; microaberrations; candidate genes; SNP array; GPR35
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.
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 288 with vesicoureteral reflux, 120 with renal hypodysplasia and 90 with unilateral renal agenesis. 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.
renal agenesis; renal development; genetic renal disease
We recently reported that centrosomal protein 164 (CEP164) regulates both cilia and the DNA damage response in the autosomal recessive polycystic kidney disease nephronophthisis. Here we examine the functional role of CEP164 in nephronophthisis-related ciliopathies and concomitant fibrosis. Live cell imaging of RPE-FUCCI (fluorescent, ubiquitination-based cell cycle indicator) cells after siRNA knockdown of CEP164 revealed an overall quicker cell cycle than control cells, although early S-phase was significantly longer. Follow-up FACS experiments with renal IMCD3 cells confirm that Cep164 siRNA knockdown promotes cells to accumulate in S-phase. We demonstrate that this effect can be rescued by human wild-type CEP164, but not disease-associated mutants. siRNA of CEP164 revealed a proliferation defect over time, as measured by CyQuant assays. The discrepancy between accelerated cell cycle and inhibited overall proliferation could be explained by induction of apoptosis and epithelial-to-mesenchymal transition. Reduction of CEP164 levels induces apoptosis in immunofluorescence, FACS and RT-QPCR experiments. Furthermore, knockdown of Cep164 or overexpression of dominant negative mutant allele CEP164 Q525X induces epithelial-to-mesenchymal transition, and concomitant upregulation of genes associated with fibrosis. Zebrafish injected with cep164 morpholinos likewise manifest developmental abnormalities, impaired DNA damage signaling, apoptosis and a pro-fibrotic response in vivo. This study reveals a novel role for CEP164 in the pathogenesis of nephronophthisis, in which mutations cause ciliary defects coupled with DNA damage induced replicative stress, cell death, and epithelial-to-mesenchymal transition, and suggests that these events drive the characteristic fibrosis observed in nephronophthisis kidneys.
Nephronophthisis is a leading inherited cause of renal failure in children and young adults. This work contributes to understanding of the disease mechanism of nephronophthisis, which is characterized by multi-cystic and fibrotic kidneys. The genes mutated in patients with nephronophthisis all seem to encode proteins involved in cilia function, and some of them are recently reported to also function in DNA damage signaling. We investigated how loss of cilia and impaired DNA damage signaling could cause the excessive fibrosis seen in nephronophthisis. Studies during the past decade have focused on treating the cysts of this early-onset renal disease. However, we think that understanding and curing the fibrosis seen in these patients will provide new treatment opportunities. Our work gives insight into the orchestration of downstream effects on the cellular level after loss of nephronophthisis gene CEP164 as a result of loss of cilia and accumulating DNA damage signaling.
Rare single-gene disorders cause chronic disease. However, half of the
6,000 recessive single gene causes of disease are still unknown. Because
recessive disease genes can illuminate, at least in part, disease
pathomechanism, their identification offers direct opportunities for improved
clinical management and potentially treatment. Rare diseases comprise the
majority of chronic kidney disease (CKD) in children but are notoriously
difficult to diagnose. Whole exome resequencing facilitates identification of
recessive disease genes. However, its utility is impeded by the large number of
genetic variants detected. We here overcome this limitation by combining
homozygosity mapping with whole exome resequencing in 10 sib pairs with a
nephronophthisis-related ciliopathy, which represents the most frequent genetic
cause of CKD in the first three decades of life. In 7 of 10 sib-ships with a
histologic or ultrasonographic diagnosis of nephronophthisis-related ciliopathy
we detect the causative gene. In six sib-ships we identify mutations of known
nephronophthisis-related ciliopathy genes, while in two additional sib-ships we
found mutations in the known CKD-causing genes SLC4A1 and
AGXT as phenocopies of nephronophthisis-related ciliopathy.
Thus whole exome resequencing establishes an efficient, non-invasive approach
towards early detection and causation-based diagnosis of rare kidney diseases.
This approach can be extended to other rare recessive disorders, thereby
providing accurate diagnosis and facilitating the study of disease
Nephronophthisis (NPHP) is an autosomal recessive cystic kidney disease, which represents the most frequent genetic cause for end-stage renal disease up to the third decade of life. Nephronophthisis is caused by mutations in eleven different genes called nephrocystins (NPHP1-11, NPHP1L). With an increasing number of identified genes our knowledge of nephronophthisis is changing and improving our understanding of the pathomechanisms in nephronophthisis. Recent publications described ciliary expression of nephrocystins together with other cystoproteins like polycystins 1 and 2, and fibrocystin. These findings have shifted our focus to a pathomechanism involving defects in ciliary function (ciliopathy) and planar cell polarity (PCP). In addition, discoveries of new nephrocystin genes have shown that the disease spectrum of nephronophthisis is much broader than previously anticipated. Different forms of mutations within the same NPHP gene can cause different disease severity. In this review we will highlighten the different hypotheses concerning the pathomechanisms for nephronophthisis and we will underline the clinical variability of nephronophthisis. The clinical spectrum has become even more complex with the possibility of oligogenicity in NPHP.
nephronophthisis; cystic kidney disease; ciliopathy; Senior-Loken syndrome; Joubert syndrome; Meckel-Gruber syndrome; molecular genetics
Nephronophthisis (NPHP) is a recessive disorder of the kidney that is the leading genetic cause of end-stage renal failure in children. Egypt is a country with a high rate of consanguineous marriages; yet, only a few studies have investigated the clinical and molecular characteristics of NPHP and related ciliopathies in the Egyptian population. We studied 20 children, from 17 independent families, fulfilling the clinical and the ultrasonographic criteria of NPHP. Analysis for a homozygous deletion of the NPHP1 gene was performed by polymerase chain reaction on the genomic DNA of all patients. Patients were best categorized as 75% juvenile NPHP, 5% infantile NPHP, and 20% Joubert syndrome-related disorders (JSRD). The mean age at diagnosis was 87.5 + 45.4 months, which was significantly late as compared with the age at onset of symptoms, 43.8 ± 29.7 months (P <0.01). Homozygous NPHP1 deletions were detected in six patients from five of 17 (29.4%) studied families. Our study demonstrates the clinical phenotype of NPHP and related disorders in Egyptian children. Also, we report that homozygous NPHP1 deletions account for 29.4% of NPHP in the studied families in this cohort, thereby confir-ming the diagnosis of type-1 NPHP. Moreover, our findings confirm that NPHP1 deletions can indeed be responsible for JSRD.
Nephronophthisis (NPHP), an autosomal recessive cystic kidney disease, is the most frequent genetic cause for end-stage renal failure in the first 3 decades of life. Mutations in 13 genes (NPHP1-NPHP11, AHI1, and CC2D2A) cause NPHP with ubiquitous expression of the corresponding proteins consistent with the multiorgan involvement of NPHP-related diseases. The genotype-phenotype correlation in these ciliopathies can be explained by gene locus heterogeneity, allelism, and the impact of modifier genes. In some NPHP-related ciliopathies, the nature of the recessive mutations determines disease severity. In order to define the genotypephenotype correlation more clearly, we evaluated a worldwide cohort of 440 patients from 365 families with NPHP-related ciliopathies, in whom both disease-causing alleles were identified. The phenotypes were ranked in the order of severity from degenerative to degenerative/ dysplastic to dysplastic. A genotype of 2 null alleles caused a range of phenotypes with an increasing order of severity of NPHP1, NPHP3, NPHP4, NPHP5, NPHP2, NPHP10, NPHP6 to AHI1. Only NPHP6 showed allelic influences on the phenotypes; the presence of 2 null mutations caused dysplastic phenotypes, whereas at least one missense allele rescued it to a milder degenerative phenotype. We also found 9 novel mutations in the NPHP genes. Thus, our studies have important implications for genetic counseling and planning of renal replacement therapy.
cystic kidney; end-stage renal disease; genetic renal disease; human genetics; pediatric nephrology
Nephronophthisis-associated ciliopathies (NPHP-AC) comprise a group of autosomal recessive cystic kidney diseases that includes nephronophthisis (NPHP), Senior-Loken syndrome (SLS), Joubert syndrome (JBTS), and Meckel-Gruber syndrome (MKS). To date, causative mutations in NPHP-AC have been described for 18 different genes, rendering mutation analysis tedious and expensive. To overcome the broad genetic locus heterogeneity we devised a strategy of DNA pooling with consecutive massively parallel resequencing (MPR).
In 120 patients with severe NPHP-AC phenotypes we prepared 5 pools of genomic DNA with 24 patients each which were used as templates in order to PCR-amplify all 376 exons of 18 NPHP-AC genes (NPHP1, INVS, NPHP3, NPHP4, IQCB1, CEP290, GLIS2, RPGRIP1L, NEK8, TMEM67, INPP5E, TMEM216, AHI1, ARL13B, CC2D2A, TTC21B, MKS1, and XPNPEP3). PCR products were then subjected to MPR on a Illumina Genome-Analyzer and mutations were subsequently assigned to their respective mutation carrier via CEL I endonuclease-based heteroduplex screening and confirmed by Sanger sequencing.
For proof of principle we used DNA from patients with known mutations and demonstrated the detection of 22 out of 24 different alleles (92% sensitivity). MPR led to the molecular diagnosis in 30/120 patients (25%) and we identified 54 pathogenic mutations (27 novel) in 7 different NPHP-AC genes. Additionally, in 24 patients we only found single heterozygous variants of unknown significance.
The combined approach of DNA pooling followed by MPR strongly facilitates mutation analysis in broadly heterogeneous single-gene disorders. The lack of mutations in 75% of patients in our cohort indicates further extensive heterogeneity in NPHP-AC.
Next-generation sequencing; Ciliopathy; Nephronophthisis
Nephronophthisis (NPH) is an autosomal recessive cystic kidney disease that leads to renal failure in childhood or adolescence. Most NPHP gene products form molecular networks. We have identified ANKS6 as a new NPHP family member that connects NEK8 (NPHP9) to INVERSIN (INVS, NPHP2) and NPHP3 to form a distinct NPHP module. ANKS6 localizes to the proximal cilium and knockdown experiments in zebrafish and Xenopus confirmed a role in renal development. Genetic screening identified six families with ANKS6 mutations and NPH, including severe cardiovascular abnormalities, liver fibrosis and situs inversus. The oxygen sensor HIF1AN (FIH) hydroxylates ANKS6 and INVS, while knockdown of Hif1an in Xenopus resembled the loss of other NPHP proteins. HIF1AN altered the composition of the ANKS6/INVS/NPHP3 module. Network analyses, uncovering additional putative NPHP-associated genes, placed ANKS6 at the center of the NPHP module, explaining the overlapping disease manifestation caused by mutations of either ANKS6, NEK8, INVS or NPHP3.
Human COQ6 encodes a monooxygenase which is responsible for the C5-hydroxylation of the quinone ring of coenzyme Q (CoQ). Mutations in COQ6 cause primary CoQ deficiency, a condition responsive to oral CoQ10 supplementation. Treatment is however still problematic given the poor bioavailability of CoQ10. We employed S. cerevisiae lacking the orthologous gene to characterize the two different human COQ6 isoforms and the mutations found in patients. COQ6 isoform a can partially complement the defective yeast, while isoform b, which lacks part of the FAD-binding domain, is inactive but partially stable, and could have a regulatory/inhibitory function in CoQ10 biosynthesis. Most mutations identified in patients, including the frameshift Q461fs478X mutation, retain residual enzymatic activity, and all patients carry at least one hypomorphic allele, confirming that the complete block of CoQ biosynthesis is lethal. These mutants are also partially stable and allow the assembly of the CoQ biosynthetic complex. In fact treatment with two hydroxylated analogues of 4-hydroxybenzoic acid, namely, vanillic acid or 3-4-hydroxybenzoic acid, restored the respiratory growth of yeast Δcoq6 cells expressing the mutant huCOQ6-isoa proteins. These compounds, and particularly vanillic acid, could therefore represent an interesting therapeutic option for COQ6 patients.
•Human COQ6 alleles are hypomorphic•Human COQ6 mutations are catalytically inactive but stable•4-Hydroxybenzoate analogues can bypass the CoQ deficiency due to COQ6 mutations•Vanillic acid could represent a potential therapeutic agent for this condition
COQ6, flavin-dependent monooxygenase; CoQ, coenzyme Q; CoQ10, coenzyme Q10; 4HB, 4-hydroxybenzoate; VA, vanillic acid; 3,4 diHB, 3,4 dihydroxybenzoic acid; SRNS, steroid resistant nephrotic syndrome; CYC1, cytochrome c1; pHBH, para-hydroxybenzoate hydroxylase; FAD, flavin adenine dinucleotide; COQ8-ADCK3, aarF domain containing kinase 3; Coenzyme Q; Vanillic acid; COQ6; Steroid-resistant nephrotic syndrome
Identification of single-gene causes of steroid-resistant nephrotic syndrome (SRNS)
has furthered the understanding of the pathogenesis of this disease. Here, using a
combination of homozygosity mapping and whole human exome resequencing, we identified
mutations in the aarF domain containing kinase 4 (ADCK4) gene in 15
individuals with SRNS from 8 unrelated families. ADCK4 was highly similar to ADCK3,
which has been shown to participate in coenzyme Q10 (CoQ10)
biosynthesis. Mutations in ADCK4 resulted in reduced
CoQ10 levels and reduced mitochondrial respiratory enzyme activity in
cells isolated from individuals with SRNS and transformed lymphoblasts. Knockdown of
adck4 in zebrafish and Drosophila recapitulated
nephrotic syndrome-associated phenotypes. Furthermore, ADCK4 was expressed in
glomerular podocytes and partially localized to podocyte mitochondria and foot
processes in rat kidneys and cultured human podocytes. In human podocytes, ADCK4
interacted with members of the CoQ10 biosynthesis pathway, including COQ6,
which has been linked with SRNS and COQ7. Knockdown of ADCK4 in podocytes resulted in
decreased migration, which was reversed by CoQ10 addition. Interestingly,
a patient with SRNS with a homozygous ADCK4 frameshift mutation had
partial remission following CoQ10 treatment. These data indicate that
individuals with SRNS with mutations in ADCK4 or other genes that
participate in CoQ10 biosynthesis may be treatable with CoQ10.
Congenital abnormalities of the kidney and urinary tract (CAKUT) constitute the most frequent cause of chronic kidney disease in children, accounting for ~50% of all cases. Although many forms of CAKUT are likely caused by single-gene defects, only few causative genes have been identified. To identify new causative genes many candidate genes need to be analyzed due to the broad genetic locus heterogeneity of CAKUT. We therefore applied our newly developed approach of DNA pooling with consecutive massively parallel exon resequencing to overcome this problem. We pooled DNA of 20 individuals and amplified by PCR all 313 exons of 30 CAKUT candidate genes. PCR products were then subjected to massively parallel exon resequencing. Mutation carriers were identified using Sanger sequencing. We repeated the experiment to cover 40 patients in total (29 with unilateral renal agenesis and 11 with other CAKUT phenotypes). We detected 5 heterozygous missense mutations in 2 candidate genes that were not previously implicated in non-syndromic CAKUT in humans, 4 mutations in the FRAS1 gene and 1 in FREM2. All mutations were absent from 96 healthy control individuals and had a PolyPhen score of >1.4 (“possibly damaging”). Recessive truncating mutations in FRAS1 and FREM2 were known to cause Fraser syndrome in humans and mice, whereas a phenotype in heterozygous carriers has not been described. We hereby identify heterozygous missense mutations in FRAS1 and FREM2 as a new cause of non-syndromic CAKUT in human.
Nephronophthisis (NPHP), an autosomal recessive cystic kidney disease, leads to chronic renal failure in children. The genes mutated in NPHP1 and NPHP4 have been identified, and a gene locus associated with infantile nephronophthisis (NPHP2) was mapped. The kidney phenotype of NPHP2 combines clinical features of NPHP and polycystic kidney disease (PKD). Here, we identify inversin (INVS) as the gene mutated in NPHP2 with and without situs inversus. We show molecular interaction of inversin with nephrocystin, the product of the gene mutated in NPHP1 and interaction of nephrocystin with β-tubulin, a main component of primary cilia. We show that nephrocystin, inversin and β-tubulin colocalize to primary cilia of renal tubular cells. Furthermore, we produce a PKD-like renal cystic phenotype and randomization of heart looping by knockdown of invs expression in zebrafish. The interaction and colocalization in cilia of inversin, nephrocystin and β-tubulin connect pathogenetic aspects of NPHP to PKD, to primary cilia function and to left-right axis determination.
Nephrotic syndrome (NS) is divided into steroid-sensitive (SSNS) and -resistant (SRNS) variants. SRNS causes end-stage kidney disease, which cannot be cured. While the disease mechanisms of NS are not well understood, genetic mapping studies suggest a multitude of unknown single-gene causes. We combined homozygosity mapping with whole-exome resequencing and identified an ARHGDIA mutation that causes SRNS. We demonstrated that ARHGDIA is in a complex with RHO GTPases and is prominently expressed in podocytes of rat glomeruli. ARHGDIA mutations (R120X and G173V) from individuals with SRNS abrogated interaction with RHO GTPases and increased active GTP-bound RAC1 and CDC42, but not RHOA, indicating that RAC1 and CDC42 are more relevant to the pathogenesis of this SRNS variant than RHOA. Moreover, the mutations enhanced migration of cultured human podocytes; however, enhanced migration was reversed by treatment with RAC1 inhibitors. The nephrotic phenotype was recapitulated in arhgdia-deficient zebrafish. RAC1 inhibitors were partially effective in ameliorating arhgdia-associated defects. These findings identify a single-gene cause of NS and reveal that RHO GTPase signaling is a pathogenic mediator of SRNS.
Focal segmental glomerulosclerosis (FSGS) is a kidney disease that presents with nephrotic syndrome and is often resistant to glucocorticosteroids and progresses to end-stage kidney disease in 50–70% of patients. Genetic studies in familial FSGS indicate that it is a disease of the podocytes, major components of the glomerular filtration barrier. However the molecular cause of over half of primary FSGS is unknown, and effective treatments have been elusive.
We performed whole-genome linkage analysis followed by high-throughput sequencing of the positive linkage area in a family with autosomal recessive FSGS and sequenced a newly discovered gene in 52 unrelated FSGS patients. Immunohistochemistry was performed in human kidney biopsies and cultured podocytes. Expression studies in vitro were performed to characterize the functional consequences of the mutations identified.
Two mutations (A159P and Y695X) in MYO1E, encoding the non-muscle class I myosin, myosin 1E (Myo1E), which segregated with FSGS in two independent pedigrees were identified. Patients were homozygous for the mutations and were resistant to glucocorticosteroids. Electron microscopy showed thickening and disorganization of the glomerular basement membrane. Normal expression of Myo1E was documented in control human kidney biopsies in vivo and in glomerular podocytes in vitro. Transfection studies revealed abnormal subcellular localization and function of A159P-Myo1E mutant. The Y695X mutation causes loss of calmodulin binding and the tail domains of Myo1E.
MYO1E mutations lead to childhood onset steroid-resistant FSGS. These data support a role of Myo1E in podocyte function and the consequent integrity of the glomerular permselectivity barrier.
Neighboring genes are often coordinately expressed within cis-regulatory modules, but evidence that nonparalogous genes share functions in mammals is lacking. Here, we report that mutation of either TMEM138 or TMEM216 causes a phenotypically indistinguishable human ciliopathy, Joubert syndrome. Despite a lack of sequence homology, the genes are aligned in a head-to-tail configuration and joined by chromosomal rearrangement at the amphibian-to-reptile evolutionary transition. Expression of the two genes is mediated by a conserved regulatory element in the noncoding intergenic region. Coordinated expression is important for their interdependent cellular role in vesicular transport to primary cilia. Hence, during vertebrate evolution of genes involved in ciliogenesis, nonparalogous genes were arranged to a functional gene cluster with shared regulatory elements.
Nephronophthisis-related ciliopathies (NPHP-RC) are degenerative recessive diseases that affect kidney, retina and brain. Genetic defects in NPHP gene products that localize to cilia and centrosomes defined them as ‘ciliopathies’. However, disease mechanisms remain poorly understood. Here we identify by whole exome resequencing, mutations of MRE11, ZNF423, and CEP164 as causing NPHP-RC. All three genes function within the DNA damage response (DDR) pathway, hitherto not implicated in ciliopathies. We demonstrate that, upon induced DNA damage, the NPHP-RC proteins ZNF423, CEP164 and NPHP10 colocalize to nuclear foci positive for TIP60, known to activate ATM at sites of DNA damage. We show that knockdown of CEP164 or ZNF423 causes sensitivity to DNA damaging agents, and that cep164 knockdown in zebrafish results in dysregulated DDR and an NPHP-RC phenotype. We identify TTBK2, CCDC92, NPHP3 and DVL3 as novel CEP164 interaction partners. Our findings link degenerative diseases of kidney and retina, disorders of increasing prevalence, to mechanisms of DDR.
Chronic kidney disease (CKD) represents a major health burden1. Its central feature of renal fibrosis is not well understood. By whole exome resequencing in a model disorder for renal fibrosis, nephronophthisis (NPHP), we identified mutations of Fanconi anemia-associated nuclease 1 (FAN1) as causing karyomegalic interstitial nephritis (KIN). Renal histology of KIN is indistinguishable from NPHP except for the presence of karyomegaly2. FAN1 has nuclease activity, acting in DNA interstrand crosslinking (ICL) repair within the Fanconi anemia pathway of DNA damage response (DDR)3–6. We demonstrate that cells from individuals with FAN1 mutations exhibit sensitivity to the ICL agent mitomycin C. However, they do not exhibit chromosome breakage or cell cycle arrest after diepoxybutane treatment, unlike cells from patients with Fanconi anemia. We complement ICL sensitivity with wild type FAN1 but not mutant cDNA from individuals with KIN. Depletion of fan1 in zebrafish revealed increased DDR, apoptosis, and kidney cysts akin to NPHP. Our findings implicate susceptibility to environmental genotoxins and inadequate DNA repair as novel mechanisms of renal fibrosis and CKD.
Homozygous or compound heterozygous Renin (REN) mutations cause renal tubular dysgenesis (RTD), which is characterized by death in utero due to renal failure and pulmonary hypoplasia. The phenotype resembles the fetopathy caused by angiotensin-converting enzyme inhibitor or angiotensin receptor blocker intake during pregnancy. Recently, heterozygous REN mutations were shown to result in early-onset hyperuricemia, anemia and chronic renal failure. So far, only three different heterozygous REN mutations were reported.
We performed mutation analysis of the REN gene in 39 kindreds with hyperuricemia and chronic kidney disease (CKD) previously tested negative for mutations in the UMOD and HNF1β genes. We identified one kindred with a novel c.28T>C (p.W10R) REN mutation in the signal sequence, concluding that REN mutations are rare events in CKD patients. Affected individuals over four generations were identified carrying the novel REN mutation and were characterized by significant anemia, hyperuricemia and CKD. Anemia was severe and disproportional to the degree of renal impairment. Moreover all heterozygous REN mutations are localized in the signal sequence. Therefore, screening of the REN gene for CKD patients with hyperuricemia and anemia may be focusing on exon 1 sequencing, which encodes the signal peptide.
Integrin α3 is a transmembrane integrin receptor subunit that mediates signals between the cells and their microenvironment. We identified three patients with homozygous mutations in the integrin α3 gene that were associated with disrupted basement-membrane structures and compromised barrier functions in kidney, lung, and skin. The patients had a multiorgan disorder that included congenital nephrotic syndrome, interstitial lung disease, and epidermolysis bullosa. The renal and respiratory features predominated, and the lung involvement accounted for the lethal course of the disease. Although skin fragility was mild, it provided clues to the diagnosis.
We describe a child of Middle Eastern descent by first-cousin mating with idiopathic neurogenic bladder and high grade vesicoureteral reflux at 1 year of age, whose characteristic facial grimace led to the diagnosis of Ochoa (Urofacial) syndrome at age 5 years. We used homozygosity mapping, exome capture and paired end sequencing to identify the disease causing mutation in the proband. We reviewed the literature with respect to the urologic manifestations of Ochoa syndrome. A large region of marker homozygosity was observed at 10q24, consistent with known autosomal recessive inheritance, family consanguinity and previous genetic mapping in other families with Ochoa syndrome. A homozygous mutation was identified in the proband in HPSE2: c.1374_1378delTGTGC, a deletion of 5 nucleotides in exon 10 that is predicted to lead to a frameshift followed by replacement of 132 C-terminal amino acids with 153 novel amino acids (p.Ala458Alafsdel132ins153). This mutation is novel relative to very recently published mutations in HPSE2 in other families. Early intervention and recognition of Ochoa syndrome with control of risk factors and close surveillance will decrease complications and renal failure.
Ochoa syndrome; Urofacial syndrome; HPSE2 mutation; Neurogenic bladder
The ciliopathies are a category of diseases caused by disruption of the physiological functions of cilia. Ciliary dysfunction results in a broad range of phenotypes, including renal, hepatic, and pancreatic cyst formation; situs abnormalities; retinal degeneration; anosmia; cerebellar or other brain anomalies; postaxial polydactyly; bronchiectasis; and infertility. The specific clinical features are dictated by the subtype, structure, distribution, and function of the affected cilia. This review highlights the clinical variability caused by dysfunction of motile and nonmotile primary cilia and emphasizes the genetic heterogeneity and phenotypic overlap that are characteristics of these disorders. There is a need for additional research to understand the shared and unique functions of motile and nonmotile cilia and the pathophysiology resulting from mutations in cilia, basal bodies, or centrosomes. Increased understanding of ciliary biology will improve the diagnosis and management of primary ciliary dyskinesia, syndromic ciliopathies, and cilia-related cystic diseases.
primary cilia; ciliopathy; heterotaxy; nephronophthisis; cyst