WT1-related disorders: more than Denys-Drash syndrome

Potential involvement of abnormal splicing in severe WT1-related disorders

INTRODUCTION

WT1-related disorders are associated with WT1 gene variants. Recent advances in genetic medicine have led to a better understanding of the genotype-phenotype correlation in WT1-related diseases, particularly missense variants in exons 8 or 9 that lead to a wide range of severities. Exonic variants can lead to splicing abnormalities in rare diseases. No reports have investigated exonic variants in WT1 that cause aberrant splicing. We examined whether exonic variants in WT1 exon 8 or 9 cause splicing abnormalities and affect disease severity.

METHODS

We selected nine rare missense variants in exon 8 or 9 in WT1 outside the DNA binding domain and C2H2 sites from the Human Gene Variant Database Professional that unexpectedly present severe phenotypes. We conducted functional splicing assays using hybrid minigenes for the nine variants containing exon 8 and 9 and surrounding sequences. Minigene vectors were transfected into cultured cells, and mRNA was analyzed. In silico analysis was performed.

RESULTS

Splicing assays revealed that one of the nine variants caused aberrant splicing, with exon 8 skipping. One previously reported case with this variant showed particularly severe phenotype, progressing to kidney failure within 3 months.

CONCLUSIONS

One WT1 variant in exon 8 or 9 disrupted the splice site, leading to aberrant splicing in vitro and potentially contributing to an unexpectedly severe phenotype for a missense variant outside the DNA binding domain and C2H2 sites. In vitro splicing assays may help clarify the genotype-phenotype correlation in WT1-related disorders, especially for variants outside canonical functional domains.

WT1-Related Nephropathy in a Phenotypically Female Child: A Case of Clinical and Genetic Discordance

WT1-related disorders comprise a spectrum of conditions resulting from mutations or deletions of the WT1 gene. Alteration in this gene have been associated with many syndromes, including WAGR syndrome, Denys-Drash syndrome (DDS), Frasier syndrome (FS) and Meacham syndrome. We present the case of an 8-year-old phenotypically female child with symptoms of end-stage kidney disease (ESKD), hypertension and anasarca, requiring renal replacement therapy. This case is distinctive due to its unusual onset, the presence of thrombotic microangiopathy (TMA), and the detection of a heterozygous missense mutation in the WT1 gene (c.1298G>A, p.Cys433Tyr) located in exon 8, in association with a 46 XY karyotype. The kidney biopsy indicated advanced focal segmental glomerulosclerosis (FSGS) with characteristics of TMA, implying a possible alternative diagnosis. In light of the heightened malignancy risk, the patient had preventative laparoscopic gonadectomy, which revealed rudimentary testicular tissues. The identified genotype points toward a diagnosis of DDS. However, the clinical presentation is more consistent with features typically seen in FS. This discrepancy highlights the significant phenotypic and genotypic overlap between the two syndromes. As a result, there is ongoing discussion in the literature about whether DDS and FS should be considered distinct clinical entities or rather variable expressions along a shared disease spectrum.

The role of chromatin-related epigenetic modulations in CAKUT

Congenital anomalies of the kidney and urinary tract (CAKUT) represent a major health burden in humans. Phenotypes range from renal hypoplasia or renal agenesis, cystic renal dysplasia, duplicated or horseshoe kidneys to obstruction of the ureteropelvic junction, megaureters, duplicated ureters, urethral valves or bladder malformations. Over the past decade, next-generation sequencing has identified numerous causative genes; however, the genetic basis of most cases remains unexplained. It is assumed that environmental factors have a significant impact on the phenotype, but, overall, the pathogenesis has remained poorly understood. Interestingly however, CAKUT is a common phenotypic feature in two human syndromes, Kabuki and Koolen-de Vries syndrome, caused by dysfunction of genes encoding for KMT2D and KANSL1, both members of protein complexes playing an important role in histone modifications. In this chapter, we discuss current knowledge regarding epigenetic modulation in renal development and a putatively under-recognized role of epigenetics in CAKUT.

A Chromosomal Microarray Detects Microdeletion at Chromosome Locus 11p14.3-p12 Leading to Wilms Tumor, Aniridia, Genitourinary Anomalies, and Mental Retardation (WAGR) Syndrome

The short form of the term "WAGR syndrome" denotes susceptibility to Wilms tumor, absence of irises, genital and urinary anomalies, and growth/development retardation. It is also called 11p deletion syndrome since varying amounts of the short arm of chromosome 11 are found deleted in these patients. The earliest presenting symptom can be undescended testes detected at birth or nystagmus, which can bring attention to the aniridia by a physician. Recognition of this disorder is important for surveilling Wilms tumor, an embryonal cancer of the kidney. A genetic diagnosis is possible by using a chromosomal microarray, fluorescent in situ hybridization, or multiplex ligation-dependent probe amplification (MLPA). The inheritance is autosomal dominant and, in most cases, the deletion is sporadic/denovo (not inherited from parents). We describe a male child with Wilm's tumor, aniridia, genitourinary anomalies, and mental retardation (WAGR) syndrome due to a microdeletion on chromosome 11 {arr[GRCh38]11p14.3p12(22,560,576_38,466,045)x1}.

Association of Atypical Hemolytic Uremic Syndrome With Wilms' Tumor 1 Gene Mutations: A Case Series and Literature Review

Atypical hemolytic uremic syndrome (aHUS) is a life‑threatening condition characterized by microangiopathic hemolytic anemia, thrombocytopenia, as well as acute kidney injury (AKI). It can occur primarily due to complement gene mutations or secondary to another underlying condition. Several cases with Wilms' tumor gene 1 (WT1) mutations that presented with aHUS have been reported. Here, we report four cases of children diagnosed with WT1 mutations and presented initially with aHUS. There are two boys and two girls who presented with thrombotic microangiopathy (TMA), high lactate dehydrogenase, fragmented red blood cell (RBCs), and severe hypertension. All of them were anuric from the first presentation. Therapy with C5 inhibitors was initiated immediately and was associated with hematological remission without renal recovery. Renal replacement therapy (RRT) was started for all of the patients. A renal biopsy was conducted on two patients and showed global glomerulosclerosis. A genetic study identified pathogenic mutations in the WT1 gene. Two of the patients became dialysis dependent, and two patients underwent renal transplantation without the recurrence of aHUS. Our case series emphasizes that a diagnosis of WT1 mutation can be considered in children with aHUS with severe renal manifestations without a response to C5 inhibitors and with global glomerulosclerosis on renal biopsy. To our knowledge, this is the first report of a series of cases of WT1 mutations in pediatric patients presenting with clinical manifestation manifestations of aHUS. This unique finding highlights an association between HUS and WT1 mutation.