NDT Advance Access originally published online on November 22, 2005
Nephrology Dialysis Transplantation 2006 21(2):518-521; doi:10.1093/ndt/gfi285
© The Author [2005]. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Case Report
A novel WT1 missense mutation presenting with Denys–Drash syndrome and cortical atrophy
Valérie Schumacher1,
Julia Thumfart2,
Matthias Drechsler1,
Maximillian Essayie3,
Brigitte Royer-Pokora1,
Uwe Querfeld2 and
Dominik Müller2
1 Institute of Human Genetics, Heinrich-Heine University Düsseldorf and 2 Department of Pediatric Nephrology and 3 Department of Pediatric Endocrinology, Charité Children's Hospital Berlin, Germany
Correspondence and offprint requests to: Dominik Müller, MD, Department of Pediatric Nephrology, Charité Children's Hospital, Augustenburger Platz 1, 13353 Berlin, Germany. Email: dominik.mueller{at}charite.de
Keywords: cortical atrophy; Denys–Drash syndrome; WT1 mutation
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Introduction
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Germline heterozygous missense mutations in the Wilms’
tumour suppressor gene 1 (
WT1) cause Denys–Drash Syndrome
(DDS), which is characterized by a progressive glomerulopathy
(mainly diffuse mesangial sclerosis), genital abnormalities
in genotypic males and a predisposition to Wilms’ tumour
[
1]. The protein exerts its function as a tissue-specific zinc
finger transcription factor by binding to the promoter of its
target genes and, thus, regulating their transcription. Loss
of WT1 function through mutations results in the misregulation
of these target genes and, subsequently, in developmental defects.
The expression pattern of
WT1 mRNA together with data obtained
from
WT1 deficient mice indicate that the function of the gene
is not restricted to the urogenital system, but involves the
development of other organs, such as spleen, adrenal glands,
heart, mesothelium, spinal cord and brain [
2–5]. We report
a novel germline
WT1 missense mutation in a genotypic male patient
with DDS and cerebral atrophy.
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Case
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The child was the second offspring of healthy, unrelated Caucasian
parents. Pregnancy was complicated by fetal cardiac arrhythmias
and myocardial hypertrophy. Both were not confirmed after birth.
Abnormalities of amniotic fluid or placenta size were not noted.
The child was born at term with a birth weight of 3100 g. A
horseshoe kidney was already diagnosed prenatally. Although
external genitalia had male appearance at birth, the child displayed
anorchia and bilateral inguinal hernias. On surgical exploration
during hernia repair, only blind ending testicular cords without
any signs of testicular or epididymic tissue were found; they
were not removed.
At the age of 6, months a routine cerebral ultrasound showed hydrocephalus e vacuo. The child developed poorly during the following months. Besides a convergent strabism, the patient showed progressive psychomotor delay. Computed tomography and magnetic resonance imaging scans during follow-up revealed cerebral cortical atrophy and thinning of corpus callosum in the first year of life (Figure 1). Funduscopy at the age of 12 months remained without pathological findings. At the age of 1 year, overt proteinuria (4.0 g/24 h/1.73 m2) was discovered accompanied with a rapid decline of renal function. At the age of 3 years, the patient was started on haemodialysis and then switched to peritoneal dialysis. At the age of 4.5 years, one half of the horseshoe kidney was removed to reduce proteinuria. Histologically, the kidney showed diffuse mesangial sclerosis. The child was successfully transplanted at the age of 5 years with a kidney graft from his father. At the time of surgery, the remnant kidney was also removed. There were no signs of malignancy (Wilms’ tumour or gonadoblastoma). DDS was therefore considered as incomplete.
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Fig. 1. Magnetic resonance image of the brain at the age of 5 years. It demonstrates cerebral atrophy and thinning of corpus callosum.
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To confirm DDS on the molecular level,
WT1 mutational analysis
was performed. Using the polymerase chain reaction (PCR)/single-strand
conformation polymorphism analysis as described previously [
6],
an altered banding pattern was found for the exon 8 PCR product.
Direct sequencing revealed a novel germline heterozygous nucleotide
exchange from G
T at position 1107 (
Figure 2A), resulting in
an amino-acid substitution from Gln
His at codon 369. As seen
in
Figure 2B, glutamine is highly conserved between different
species and its exchange to histidine causes major changes in
the secondary structure of zinc finger 2 (
Figure 2C), which
may result in loss of DNA-binding capacities. None of the parents
was carrying the mutation, indicating a
de novo mutation.
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Fig. 2. (A) Sequencing chromatogram of the reverse strand from exon 8. The nucleotide exchange is marked by an arrow and the corresponding amino-acid change is shown. (B) Comparison of a part from the WT1 protein sequence between different species. The affected glutamine (Q) is highlighted by a box. Xenla, Xenopus laevis; BRARE, zebrafish; ALLMI: Alligator mississippiensis; FUGRU, Fugu. (C) Secondary sequence prediction from zinc finger 2 of the wild type WT1, of our patient and the patient from Ohta et al. [8] generated using the sequNNPREDICT programme (www.cmpharm.ucsf.edu/~nomi/nnpredict.html).
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Since the patient presented with a complex phenotype, especially
with psychomotor delay, we asked whether additional cytogenetic
changes could account for these symptoms. However, high-resolution
karyotyping (500 bands) remained without pathological findings
(data not shown). In addition, we screened for submicroscopic
deletions in the vicinity of the
WT1 gene as this region is
known to be deleted in patients with WAGR syndrome, presenting
with a high risk for Wilms’ tumours, aniridia, genital
abnormalities in males and mental retardation. For this, we
performed, as previously described [
7], a fluorescence
in situ hybridization with one probe covering the 3' region of the
WT1 gene (HD12) and another one covering the region located between
the
WT1 gene and the aniridia gene
Pax6 (p60). Thereby, we could
exclude the presence of submicroscopic deletions in this region
(
Figure 3).
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Fig. 3. Simultaneous fluorescence in situ hybridization with two probes from chromosome 11p13 and 11p15. The 11p13 probes (HD12 and p60) are marked with a white arrow. The 11p15 control probe is not marked.
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Discussion
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The prime role of WT1 in the pathogenesis of several disorders
like DDS, Frasier syndrome and WAGR syndrome is substantiated
by the demonstration of mutations or deletions in the
WT1 gene.
Here, we present a case of DDS with a novel germline heterozygous
WT1 mutation. The gene product is predicted to have lost its
capacity for DNA binding due to changes in the secondary protein
structure. Ohta
et al. [
8] have found the same amino acid (Gln
369) to be affected in a DDS patient. However, in their case,
glutamine was replaced by arginine. Interestingly, their patient
showed only a mild renal phenotype, with nephrotic syndrome
first diagnosed at the age of 5 years and only a slight progression
over the course of 18 years. The prediction of the secondary
protein structure showed less pronounced changes compared with
the mutation in our patient (
Figure 2C).
Our patient shows features not typically found in DDS. First, he shows normal male genitalia and complete absence of testicular tissue. The fact that the child did not display hypospadia might point at the presence of disappearing testosterone-producing tissue during development (‘vanishing testes’). Second, he presents with a horseshoe kidney. Until now it is not known whether WT1 mutations account for this abnormality, but interestingly, an increased incidence of Wilms’ tumour has been noted in patients with a horseshoe kidney. As 10–15% of all Wilms’ tumours are caused by WT1 mutations, this mutation could be responsible for a horseshoe kidney. Third, the patient showed cerebral abnormalities. It is currently unknown to what extent WT1 mutations may also account for a phenotype in other tissues expressing WT1, such as the central nervous system. During mouse and rat development, WT1 is found to be expressed in ependymal cells of the spinal cord and in the area postrema of the brain, where expression continues postnatally, suggesting a role throughout lifetime [3,4]. Furthermore, recent findings indicate that WT1 deficient mice have thinner retinas with apoptotic loss of a large fraction of retinal ganglion cell precursors [9]. Together, these observations suggest that WT1 may also play a role in the development of neural structures and may be required for neuronal differentiation. This is also supported by the observation that PC19 embryonal carcinoma cells, induced with retinoic acid, turn on WT1 expression and differentiate into glial and neuronal cells [10]. Only little is known about WT1 expression in human brain. It was found to be expressed in different areas of the adult brain, such as occipital lobe, frontal lobe, hind brain, cerebellum and pons [11]. In addition, there is evidence that WT1 is associated with neuronal degeneration [12].
Although WT1 is expressed in the brain, patients with WT1 mutations have not been reported to show neurological symptoms. Our DDS case presented here showed psychochomotor delay and cortical cerebral atrophy preceding the onset of renal disease. In the literature, there are only two reports on DDS combined with neurological abnormalities: one patient with psychomotor delay and cerebral atrophy; the other with gross motor delay [13]. As we could exclude cytogenetic changes and small deletions in the WAGR region, the question arises whether WT1 mutations may account for the neurological phenotype. In other words, cerebral atrophy in these cases could be a sign of a deficient neural development caused by mutation in the WT1 gene. We suggest therefore that the diagnosis of WT1 mutations should always be accompanied by in-depth neurological examination.
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Acknowledgments
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We thank Dr Barbara Hildebrandt for performing the karyotype
analysis. D.M. is a member of the EU (FP6) founded European
Renal Genome Project (FP6005085).
Conflict of interest statement. None declared.
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References
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Received for publication: 10. 8.05
Accepted in revised form: 3.11.05
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