Donor splice-site mutations in WT1 are responsible for Frasier syndrome

Abstract

Frasier syndrome (FS) is a rare disease defined by male pseudo-hermaphroditism and progressive glomerulopathy. Patients present with normal female external genitalia, streak gonads and XY karyotype and frequently develop gonadoblastoma. Glomerular symptoms consist of childhood proteinuria and nephrotic syndrome, characterized by unspecific focal and segmental glomerular sclerosis, progressing to end-stage renal failure in adolescence or early adulthood. No case of Wilms' tumour has been reported, even in patients with extended follow-up. In contrast with FS patients, most individuals with Denys-Drash syndrome (DDS; refs 6,7) have ambiguous genitalia or a female phenotype, an XY karyotype and dysgenetic gonads. Renal symptoms are characterized by diffuse mesangial sclerosis, usually before the age of one year, and patients frequently develop Wilms' tumour. Mutations of the Wilms'-tumour gene, WT1, cause different pathologies of the urogenital system, including DDS. WT1 is composed of ten exons and encodes a protein with four zinc-finger motifs and transcriptional and tumour-suppressor activities. Alternative splicing generates four isoforms: the fifth exon may or may not be present, and an alternative splice site in intron 9 allows the addition of three amino acids (KTS) between the third and fourth zinc fingers of WT1 (ref. 17). Here we demonstrate that FS is caused by mutations in the donor splice site in intron 9 of WT1, with the predicted loss of the +KTS isoform. Examination of WT1 transcripts indeed showed a diminution of the +KTS/-KTS isoform ratio in patients with FS.

hnRNP-U directly interacts with WT1 and modulates WT1 transcriptional activation

“…It is likely that for normal WT1 function, the full complement of endogenously expressed isoforms is required. This hypothesis is consistent with the observation that Frasier syndrome (male pseudohermaphroditism and progressive glomerulopathy) is caused by a loss of þ KTS isoform expression from only one allele, thereby subtly altering the þ /ÀKTS ratio (Barbaux et al, 1997).…”

Clinical and Molecular Characterization of Patients with Heterozygous Mutations in Wilms Tumor Suppressor Gene 1

“…Heterozygous germline mutations in WT1 were described in two rare human conditions: Denys-Drash syndrome (DDS) with exon mutations in the zinc-finger region (7,8) and Frasier syndrome (FS) with mutations affecting the canonic donor KTS splice site of intron 9 (9,10). DDS includes steroid-resistant nephrotic syndrome rapidly progressing to ESRD, 46 XY disorder in sex development (DSD) with sex reversal and a high risk for WT (11,12).…”

Real-time PCR quantification of major Wilms’ tumor gene 1 (WT1) isoforms in acute myeloid leukemia, their characteristic expression patterns and possible functional consequences

“…10 An altered ratio of WT1 KTS[ þ ]/ KTS[ À ] variants caused by defective splicing has been described in rare pre-malignant syndromes (Frasier syndrome, Denys-Drash syndrome). [28][29][30][31] In AML, significantly higher expression levels of EX5[ þ ] variants at diagnosis and at relapse have been detected. 26,32,33 In addition, the alternative AWT1 transcript has been found to be overexpressed in leukemia samples.…”