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Salt in my soul : an unfinished life
\"Diagnosed with cystic fibrosis at the age of three, Mallory Smith grew into a determined, talented young woman who inspired others even as she raged against her illness. Despite the daily challenges of endless medical treatments and a deep understanding that she'd never lead a normal life, Mallory was determined to 'live happy,' a mantra she followed until her death\"-- Provided by publisher.
Book
Joubert syndrome: congenital cerebellar ataxia with the molar tooth
Joubert syndrome is a congenital cerebellar ataxia with autosomal recessive or X-linked inheritance, the diagnostic hallmark of which is a unique cerebellar and brainstem malformation recognisable on brain imaging—the so-called molar tooth sign. Neurological signs are present from the neonatal period and include hypotonia progressing to ataxia, global developmental delay, ocular motor apraxia, and breathing dysregulation. These signs are variably associated with multiorgan involvement, mainly of the retina, kidneys, skeleton, and liver. 21 causative genes have been identified so far, all of which encode for proteins of the primary cilium or its apparatus. The primary cilium is a subcellular organelle that has key roles in development and in many cellular functions, making Joubert syndrome part of the expanding family of ciliopathies. Notable clinical and genetic overlap exists between distinct ciliopathies, which can co-occur even within families. Such variability is probably explained by an oligogenic model of inheritance, in which the interplay of mutations, rare variants, and polymorphisms at distinct loci modulate the expressivity of the ciliary phenotype.
Journal Article
Nephronophthisis
Nephronophthisis (NPHP) is an autosomal recessive cystic kidney disease and the most frequent genetic cause of end-stage renal disease up to the third decade of life. It is caused by mutations in 11 different genes, denoted nephrocystins (
NPHP1–11
,
NPHP1L
). As an increasing number of these genes are identified, our knowledge of nephronophthisis is changing, thereby improving our understanding of the pathomechanisms in NPHP. Recent publications have described ciliary expression of nephrocystins together with other cystoproteins, such as 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 NPHP is much broader than previously anticipated. Different forms of mutations within the same
NPHP
gene can cause different disease severity. In this review, we highlight the different hypotheses on the pathomechanisms for NPHP and underline the clinical variability of this disease. The clinical spectrum has become even more complex with the possibility of oligogenicity in NPHP.
Journal Article
New insights into the role of HNF-1β in kidney (patho)physiology
Hepatocyte nuclear factor-1β (HNF-1β) is an essential transcription factor that regulates the development and function of epithelia in the kidney, liver, pancreas, and genitourinary tract. Humans who carry HNF1B mutations develop heterogeneous renal abnormalities, including multicystic dysplastic kidneys, glomerulocystic kidney disease, renal agenesis, renal hypoplasia, and renal interstitial fibrosis. In the embryonic kidney, HNF-1β is required for ureteric bud branching, initiation of nephrogenesis, and nephron segmentation. Ablation of mouse Hnf1b in nephron progenitors causes defective tubulogenesis, whereas later inactivation in elongating tubules leads to cyst formation due to downregulation of cystic disease genes, including Umod, Pkhd1, and Pkd2. In the adult kidney, HNF-1β controls the expression of genes required for intrarenal metabolism and solute transport by tubular epithelial cells. Tubular abnormalities observed in HNF-1β nephropathy include hyperuricemia with or without gout, hypokalemia, hypomagnesemia, and polyuria. Recent studies have identified novel post-transcriptional and post-translational regulatory mechanisms that control HNF-1β expression and activity, including the miRNA cluster miR17 ∼ 92 and the interacting proteins PCBD1 and zyxin. Further understanding of the molecular mechanisms upstream and downstream of HNF-1β may lead to the development of new therapeutic approaches in cystic kidney disease and other HNF1B-related renal diseases.
Journal Article
Immunofluorescence analyses of respiratory epithelial cells aid the diagnosis of nephronophthisis
Background
Nephronophthisis (NPH) comprises a heterogeneous group of inherited renal ciliopathies clinically characterized by progressive kidney failure. So far, definite diagnosis is based on molecular testing only. Here, we studied the feasibility of NPHP1 and NPHP4 immunostaining of nasal epithelial cells to secure and accelerate the diagnosis of NPH.
Methods
Samples of 86 individuals with genetically determined renal ciliopathies were analyzed for NPHP1 localization using immunofluorescence microscopy (IF). A sub-cohort of 35 individuals was also analyzed for NPHP4 localization. Western blotting was performed to confirm IF results.
Results
NPHP1 and NPHP4 were both absent in all individuals with disease-causing
NPHP1
variants including one with a homozygous missense variant (c.1027G > A; p.Gly343Arg) formerly classified as a “variant of unknown significance.” In individuals with an
NPHP4
genotype, we observed a complete absence of NPHP4 while NPHP1 was severely reduced. IF results were confirmed by immunoblotting. Variants in other genes related to renal ciliopathies did not show any impact on NPHP1/NPHP4 expression. Aberrant immunostaining in two genetically unsolved individuals gave rise for a further genetic workup resulting in a genetic diagnosis for both with disease-causing variants in
NPHP1
and
NPHP4
, respectively.
Conclusions
IF of patient-derived respiratory epithelial cells may help to secure and accelerate the diagnosis of nephronophthisis—both by verifying inconclusive genetic results and by stratifying genetic diagnostic approaches. Furthermore, we provide in vivo evidence for the interaction of NPHP1 and NPHP4 in a functional module.
Graphical abstract
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Supplementary information
Journal Article
Molecular genetic findings and clinical correlations in 100 patients with Joubert syndrome and related disorders prospectively evaluated at a single center
Purpose:
Joubert syndrome (JS) is a genetically and clinically heterogeneous ciliopathy characterized by distinct cerebellar and brainstem malformations resulting in the diagnostic “molar tooth sign” on brain imaging. To date, more than 30 JS genes have been identified, but these do not account for all patients.
Methods:
In our cohort of 100 patients with JS from 86 families, we prospectively performed extensive clinical evaluation and provided molecular diagnosis using a targeted 27-gene Molecular Inversion Probes panel followed by whole-exome sequencing (WES).
Results:
We identified the causative gene in 94% of the families; 126 (27 novel) unique potentially pathogenic variants were found in 20 genes, including
KIAA0753
and
CELSR2
, which had not previously been associated with JS. Genotype–phenotype correlation revealed the absence of retinal degeneration in patients with
TMEM67
,
C5orf52
, or
KIAA0586
variants. Chorioretinal coloboma was associated with a decreased risk for retinal degeneration and increased risk for liver disease.
TMEM67
was frequently associated with kidney disease.
Conclusion:
In JS, WES significantly increases the yield for molecular diagnosis, which is essential for reproductive counseling and the option of preimplantation and prenatal diagnosis as well as medical management and prognostic counseling for the age-dependent and progressive organ-specific manifestations, including retinal, liver, and kidney disease.
Genet Med
advance online publication 26 January 2017
Journal Article
Super-resolution microscopy reveals that disruption of ciliary transition-zone architecture causes Joubert syndrome
Ciliopathies, including nephronophthisis (NPHP), Meckel syndrome (MKS) and Joubert syndrome (JBTS), can be caused by mutations affecting components of the transition zone, a domain near the base of the cilium that controls the protein composition of its membrane. We defined the three-dimensional arrangement of key proteins in the transition zone using two-colour stochastic optical reconstruction microscopy (STORM). NPHP and MKS complex components form nested rings comprised of nine-fold doublets. JBTS-associated mutations in
RPGRIP1L
or
TCTN2
displace certain transition-zone proteins. Diverse ciliary proteins accumulate at the transition zone in wild-type cells, suggesting that the transition zone is a waypoint for proteins entering and exiting the cilium. JBTS-associated mutations in
RPGRIP1L
disrupt SMO accumulation at the transition zone and the ciliary localization of SMO. We propose that the disruption of transition-zone architecture in JBTS leads to a failure of SMO to accumulate at the transition zone and cilium, disrupting developmental signalling in JBTS.
Shi
et al.
map the ciliary transition zone by STORM imaging, characterizing protein arrangements in nested rings and finding that mutations in
RPGRIP1L
that are associated with the ciliopathy Joubert syndrome disrupt SMO ciliary localization.
Journal Article
Ciliopathy-related B9 protein complex regulates ciliary axonemal microtubule posttranslational modifications and initiation of ciliogenesis
Ciliary dysfunction results in multiorgan developmental diseases, collectively known as ciliopathies. The B9D1-B9D2-MKS1protein complex maintains the gatekeeper function at the ciliary transition zone (TZ). However, the function of B9 proteins and the mechanisms underlying why different variants in the same B9 gene cause different ciliopathies are not fully understood. Here, we investigated the function of B9 proteins and revealed 2 critical functions. First, the B9 complex interacted with and anchored TMEM67 to the TZ membrane. Disruption of the B9-TMEM67 complex reduced posttranslational modifications of axonemal microtubules due to deregulation of tubulin-modifying enzymes within cilia. Second, B9 proteins localized to centrioles prior to ciliogenesis, where they facilitated the initiation of ciliogenesis. In addition, we identified B9D2 variants in a cohort of patients with Joubert syndrome. We found that Joubert syndrome-associated B9D2 variants primarily affected axonemal microtubule modifications without disrupting ciliogenesis, whereas the Meckel syndrome-associated B9D2 variant disrupted both ciliogenesis and axonemal microtubule modifications. Thus, besides its role as a gatekeeper for ciliary membrane proteins, the B9 complex also controls axonemal microtubule posttranslational modifications and early stages of ciliogenesis, providing insights into the distinct pathologies arising from different variants of the same gene.
Journal Article
Incidental finding of acquired cystic kidney disease associated renal cell carcinoma in an adolescent with kidney failure
Acquired cystic kidney disease (ACKD) can occur in patients with chronic kidney disease and kidney failure, and its incidence increases with the duration of dialysis. In adults, ACKD is less common in the pre-dialysis group (~ 7%), but its incidence can be as high as 80% for those who are on dialysis for more than ten years. There is, however, very little information about the prevalence of ACKD in children. We report a case of malignant transformation of ACKD following a kidney transplant, highlighting the importance of surveillance of the native kidneys in paediatric patients who have been in long-term kidney replacement therapy.
Journal Article
Joubert syndrome: a model for untangling recessive disorders with extreme genetic heterogeneity
BackgroundJoubert syndrome (JS) is a recessive neurodevelopmental disorder characterised by hypotonia, ataxia, cognitive impairment, abnormal eye movements, respiratory control disturbances and a distinctive mid-hindbrain malformation. JS demonstrates substantial phenotypic variability and genetic heterogeneity. This study provides a comprehensive view of the current genetic basis, phenotypic range and gene–phenotype associations in JS.MethodsWe sequenced 27 JS-associated genes in 440 affected individuals (375 families) from a cohort of 532 individuals (440 families) with JS, using molecular inversion probe-based targeted capture and next-generation sequencing. Variant pathogenicity was defined using the Combined Annotation Dependent Depletion algorithm with an optimised score cut-off.ResultsWe identified presumed causal variants in 62% of pedigrees, including the first B9D2 mutations associated with JS. 253 different mutations in 23 genes highlight the extreme genetic heterogeneity of JS. Phenotypic analysis revealed that only 34% of individuals have a ‘pure JS’ phenotype. Retinal disease is present in 30% of individuals, renal disease in 25%, coloboma in 17%, polydactyly in 15%, liver fibrosis in 14% and encephalocele in 8%. Loss of CEP290 function is associated with retinal dystrophy, while loss of TMEM67 function is associated with liver fibrosis and coloboma, but we observe no clear-cut distinction between JS subtypes.ConclusionsThis work illustrates how combining advanced sequencing techniques with phenotypic data addresses extreme genetic heterogeneity to provide diagnostic and carrier testing, guide medical monitoring for progressive complications, facilitate interpretation of genome-wide sequencing results in individuals with a variety of phenotypes and enable gene-specific treatments in the future.
Journal Article