Mutational screening of the Wilms's tumour gene, WT1, in males with genital abnormalities

Alteration in DNA-binding affinity of Wilms tumor 1 protein due to WT1 genetic variants associated with steroid - resistant nephrotic syndrome in children

Approximately one third of children with steroid-resistant nephrotic syndrome (SRNS) carry pathogenic variants in one of the many associated genes. The WT1 gene coding for the WT1 transcription factor is among the most frequently affected genes. Cases from the Czech national SRNS database were sequenced for exons 8 and 9 of the WT1 gene. Eight distinct exonic WT1 variants in nine children were found. Three children presented with isolated SRNS, while the other six manifested with additional features. To analyze the impact of WT1 genetic variants, wild type and mutant WT1 proteins were prepared and the DNA-binding affinity of these proteins to the target EGR1 sequence was measured by microscale thermophoresis. Three WT1 mutants showed significantly decreased DNA-binding affinity (p.Arg439Pro, p.His450Arg and p.Arg463Ter), another three mutants showed significantly increased binding affinity (p.Gln447Pro, p.Asp469Asn and p.His474Arg), and the two remaining mutants (p.Cys433Tyr and p.Arg467Trp) showed no change of DNA-binding affinity. The protein products of WT1 pathogenic variants had variable DNA-binding affinity, and no clear correlation with the clinical symptoms of the patients. Further research is needed to clarify the mechanisms of action of the distinct WT1 mutants; this could potentially lead to individualized treatment of a so far unfavourable disease.

Long-term kidney function in children with Wilms tumour and constitutional WT1 pathogenic variant

BACKGROUND

Wilms tumour (WT) survivors, especially patients with associated syndromes or genitourinary anomalies due to constitutional WT1 pathogenic variant, have increased risk of kidney failure. We describe the long-term kidney function in children with WT and WT1 pathogenic variant to inform the surgical strategy and oncological management of such complex children.

METHODS

Retrospective analysis of patients with WT and constitutional WT1 pathogenic variant treated at a single centre between 1993 and 2016, reviewing genotype, phenotype, tumour histology, laterality, treatment, patient survival, and kidney outcome.

RESULTS

We identified 25 patients (60% male, median age at diagnosis 14 months, range 4-74 months) with WT1 deletion (4), missense (2), nonsense (8), frameshift (7), or splice site (4) pathogenic variant. Thirteen (52%) had bilateral disease, 3 (12%) had WT-aniridia, 1 had incomplete Denys-Drash syndrome, 11 (44%) had genitourinary malformation, and 10 (40%) had no phenotypic anomalies. Patient survival was 100% and 3 patients were in remission after relapse at median follow-up of 9 years. Seven patients (28%) commenced chronic dialysis of which 3 were after bilateral nephrectomies. The overall kidney survival for this cohort as mean time to start of dialysis was 13.38 years (95% CI: 10.3-16.4), where 7 patients experienced kidney failure at a median of 5.6 years. All of these 7 patients were subsequently transplanted. In addition, 2 patients have stage III and stage IV chronic kidney disease and 12 patients have albuminuria and/or treatment with ACE inhibitors. Four patients (3 frameshift; 1 WT1 deletion) had normal blood pressure and kidney function without proteinuria at follow-up from 1.5 to 12 years.

CONCLUSIONS

Despite the known high risk of kidney disease in patients with WT and constitutional WT1 pathogenic variant, nearly two-thirds of patients had sustained native kidney function, suggesting that nephron-sparing surgery (NSS) should be attempted when possible without compromising oncological risk. Larger international studies are needed for accurate assessment of WT1genotype-kidney function phenotype correlation.

Description of mutation spectrum and polymorphism of Wilms' tumor 1 (WT1) gene in hypospadias patients in the Indonesian population

INTRODUCTION

Hypospadias is one of the most common congenital anomalies of the penis. Previous studies reported mutation of the Wilms' tumor 1 (WT1) gene as a cause of hypospadias. The aim of this study is to describe the WT1 mutation spectrum and polymorphism in hypospadias patients in Indonesia.

MATERIAL AND METHODS

DNA was isolated from 74 hypospadias patients at the Division of Pediatric Surgery, Department of Surgery Hasan Sadikin Hospital. All exons in the WT1 gene were amplified by a PCR method, followed by Sanger sequencing. Mutation analysis was performed using BioEdit software and in silico analysis using Mutation Taster, Polymorphism Phenotyping-2 (PolyPhen-2), and Sorting Intolerant from Tolerant (SIFT).

RESULT

DNA analysis results showed two types of heterozygous mutations in five subjects (Table), hence the frequency of WT1 mutations was 6.7% (10/148 allele). The first mutation was a missense mutation identified in twin boys. The second was a novel heterozygous alteration in the non-coding region nine bp upstream of exon 6 (c.366-9T>C), which was identified in three patients. One heterozygous polymorphism in the coding region of exon 7 (c.471A>G/rs16754) was identified in 10 subjects. This variant did not cause any change in amino acid products (silence polymorphism). Allele frequency for the G allele (mutant allele) and A allele (wild type) was 13.5% and 86.5%, respectively.

DISCUSSION

WT1 is one of the best known hypospadias genes. The WT1 gene is involved in male genital development in the early and late periods of sex determination, and hence is known as a long-term expression gene in genitalia development. Mutation analysis of WT1 in a Chinese population identified that the WT1 mutation frequency was 4.4%. The WT1 mutation frequency identified in the present study was higher, at 6.7%. Coincidentally, research subjects with p.R158H variants were monozygotic twin siblings with midshaft hypospadias accompanied by undescended testis in one and penoscrotal hypospadia with micropenis in the other. The incidence of familial hypospadias in male siblings suffering from hypospadias was reported to be 9.6% in a study conducted by Sorensen et al. Moreover, in the present study polymorphism c.471A>G(rs16754) at exon 7 was identified heterozygously in 10 research subjects (minor allele frequency 13.5%).

CONCLUSION

WT1 mutations were identified in only a few cases of hypospadias and most of these were syndromic. This result implies that mutation of WT1 is not a common cause of hypospadias in the Indonesian population.

Screening of WT1 mutations in exon 8 and 9 in children with steroid resistant nephrotic syndrome from a single centre and establishment of a rapid screening assay using high-resolution melting analysis in a clinical setting

BACKGROUND

Mutations in Wilm's tumor 1 (WT1) gene is one of the commonly reported genetic mutations in children with steroid resistant nephrotic syndrome (SRNS). We report the results of direct sequencing of exons 8 and 9 of WT1 gene in 100 children with SRNS from a single centre. We standardized and validated High Resolution Melt (HRM) as a rapid and cost effective screening step to identify individuals with normal sequence and distinguish it from those with a potential mutation. Since only mutation positive samples identified by HRM will be further processed for sequencing it will help in reducing the sequencing burden and speed up the screening process.

METHODS

One hundred SRNS children were screened for WT1 mutations in Exon 8 and 9 using Sanger sequencing. HRM assay was standardized and validated by performing analysis for exon 8 and 9 on 3 healthy control and 5 abnormal variants created by site directed mutagenesis and verified by sequencing. To further test the clinical applicability of the assay, we screened additional 91 samples for HRM testing and performed a blinded assessment.

RESULTS

WT1 mutations were not observed in the cohort of children with SRNS. The results of HRM analysis were concordant with the sequencing results.

CONCLUSION

The WT1 gene mutations were not observed in the SRNS cohort indicating it has a low prevalence. We propose applying this simple, rapid and cost effective assay using HRM technique as the first step for screening the WT1 gene hot spot region in a clinical setting.

Steroid-resistant nephrotic syndrome caused by novel WT1 mutation inherited from a mosaic parent

Steroid-resistant nephrotic syndrome (SRNS) is a severe childhood disorder frequently progressing toward renal failure. Among its genetic causes are mutations in the Wilms tumor gene, WT1, which codes for a transcription factor with key role for the embryonic development of the genitourinary tract as well as for maintaining podocyte differentiation and slit diaphragm structure in adults. Defects in WT1 are associated with sporadic cases of both syndromic and isolated SRNS. We report here a novel WT1 mutation associated with SRNS in a female patient, which leads to a Cys428Ser substitution on protein level, affecting one of the cysteine residues responsible for zinc binding in the second zinc finger domain. Surprisingly, the mutation identified in the patient was found to be inherited from the healthy mosaic mother. The presence of mosaicism was confirmed using quantitative polymerase chain reaction (PCR) high-resolution melting. The clinical implications of this finding for the family are discussed.

Perspectives in Pediatric Pathology, Chapter 5. Gonadal Dysgenesis

One of the most challenging areas in pediatric testicular pathology is the appropriate understanding and pathological diagnosis of disorders of sexual development (DSD), and in particular, the issue of gonadal dysgenesis. Here we present the main concepts necessary for their understanding and appropriate classification, with extensive genetic correlations.

Translational genetics for diagnosis of human disorders of sex development

Disorders of sex development (DSDs) are congenital conditions with discrepancies between the chromosomal, gonadal, and phenotypic sex of the individual. Such disorders have historically been difficult to diagnose and cause great stress to patients and their families. Genetic analysis of human samples has been instrumental in elucidating the molecules and pathways involved in the development of the bipotential gonad into a functioning testis or ovary. However, many DSD patients still do not receive a genetic diagnosis. New genetic and genomic technologies are expanding our knowledge of the underlying mechanism of DSDs and opening new avenues for clinical diagnosis. We review the genetic technologies that have elucidated the genes that are well established in sex determination in humans, discuss findings from more recent genomic technologies, and propose a new paradigm for clinical diagnosis of DSDs.

Bilateral Wilms tumor and early presentation in pediatric patients is associated with the truncation of the Wilms tumor 1 protein

OBJECTIVES

To investigate the frequency of constitutional Wilms tumor 1 gene (WT1) abnormalities in children with bilateral Wilms tumor (WT) and the age of tumor onset in patients with a mutation.

STUDY DESIGN

Eight patients with bilateral WT were studied. High-resolution melting and direct sequencing were used to screen for the WT1 gene. Western blotting was performed to determine whether the identified mutations were associated with expressed truncated WT1 protein.

RESULTS

The median age of tumor onset in patients with a mutation in the WT1 was lower (10 months) than in those without a mutation (39 months). Three novel heterozygous nonsense mutations were identified in exon 8 in peripheral blood from 3 individuals, whereas all 3 tumor tissues lacked the wild-type allele. All mutations led to a premature stop codon with truncation of the WT1 protein. In 1 patient, a truncated form of WT1 protein was identified, suggesting that development of the WT may have resulted from expression of an abnormal protein. Four distinct silent single-nucleotide polymorphisms (SNPs) were detected. All 3 patients with a pathogenic WT1 mutation had 2 synonymous SNPs, whereas only 1 of the remaining 5 patients had a single synonymous SNP (P < .05).

CONCLUSIONS

Bilateral WT are associated with early presentation in pediatric patients and a high frequency of WT1 nonsense mutations in exon 8. Silent SNPs may also be involved in the development of WT.

Exclusion of WTAP and HOXA13 as candidate genes for isolated hypospadias

OBJECTIVE

Different molecular factors have been identified as being associated with isolated or syndrome-associated forms of hypospadias. Nevertheless, the etiology of hypospadias is unknown in 70% of cases. As mutations in the homeobox gene A13 (HOXA13) were all found to be associated with hypospadias in affected males, some types of mutation may solely lead to the isolated form. Moreover, mutations in the Wilms' tumor suppressor gene WT1 have been found in patients with hypospadias without evidence of a Wilms' tumor and, therefore, its recently identified associated protein (WTAP) may be a further candidate gene for the genesis of hypospadias.

MATERIAL AND METHODS

A total of 37 patients affected with different forms of isolated hypospadias were analyzed for mutations in their HOXA13 and WTAP genes.

RESULTS

With the exception of two novel WTAP polymorphisms, no mutations could be observed.

CONCLUSIONS

There seems to be no evidence that isolated hypospadias is commonly caused by mutations in HOXA13 or WTAP genes.

A novel WT1 mutation in a 46,XY boy with congenital bilateral cryptorchidism, nystagmus and Wilms tumor

The WT1 gene plays a crucial role in urogenital and gonadal development. Germline WT1 alterations have been described in a wide spectrum of pathological conditions, including kidney diseases, genital abnormalities and Wilms tumor (WT), frequently occurring in combination. We report on a novel WT1 nonsense mutation (c.1105C>T), introducing a premature stop codon in exon 8 (p.Q369X), in a young XY male patient who presented with bilateral cryptorchidism, nystagmus, mild proteinuria and WT, but no sign of severe nephropathy. Although the majority of congenital urogenital abnormalities are not due to constitutional defects of the WT1 gene, our findings provide a rational for considering WT1 mutational analysis as one of the screening options in newborns with congenital defects of the urogenital tract due to the associated high risk of WT.

Mutations in the Wilms' tumor 1 gene cause isolated steroid resistant nephrotic syndrome and occur in exons 8 and 9

Primary steroid-resistant nephrotic syndrome (SRNS) is characterized by childhood onset of proteinuria and progression to end-stage renal disease. Approximately 10-25% of familial and sporadic cases are caused by mutations in NPHS2 (podocin). Mutations in exons 8 and 9 of the WT1 gene have been found in patients with isolated SRNS and in SRNS associated with Wilms' tumor (WT) or urogenital malformations. However, no large studies have been performed to date to examine whether WT1 mutations in isolated SRNS are restricted to exons 8 and 9. To address this question, we screened a worldwide cohort of 164 cases of sporadic SRNS for mutations in all 10 exons of the WT1 gene by multiplex capillary heteroduplex analysis and direct sequencing. NPHS2 mutations had been excluded by direct sequencing. Fifteen patients exhibited seven different mutations exclusively in exons 8 and 9 of WT1. Although it is possible that pathogenic mutations of WT1 may also reside in the introns, regions of the gene that were not able to be screened in this study, these data together with our previous results (Ruf et al.: Kidney Int 66: 564-570, 2004) indicate that screening of WT1 exons 8 and 9 in patients with sporadic SRNS is sufficient to detect pathogenic WT1 mutations and may open inroads into differential therapy of SRNS.

Twenty-four new cases of WT1 germline mutations and review of the literature: genotype/phenotype correlations for Wilms tumor development

We report here 24 new Wilms tumor (WT) patients with germline WT1 alterations and a synopsis of our own previously described and literature cases in whom age of tumor-onset, gender, and laterality were known. This combined database contains 282 patients, 117 patients with and 165 without WT1 germline alterations. Using this information we have determined the median age of tumor-onset for patients with (12.5 months) and without WT1 gene alterations (36 months). The earliest onset was in patients with truncation (12 mo, 66 patients), followed by missense mutations (18 mo, 30 patients) and deletions (22 mo, 21 patients). Patients with the two most frequent nonsense mutations R362X and R390X and the Denys-Drash syndrome (DDS) hot spot mutation R394W/Q/L had a very early onset (9, 12, and 18 mo, respectively). The highest number of bilateral tumors was observed in the group of truncation mutations, with a higher percentage of bilateral tumors when truncations occurred in the 5' half of the WT1 gene. In addition to genital tract anomalies (GU), early onset nephrotic syndrome with diffuse mesangial sclerosis and stromal-predominant histology, tumor bilaterality, and early age of onset can now be added to the list of risk factors for carrying a germline WT1 mutation.

A WT1 exon 1 mutation in a child diagnosed with Denys-Drash syndrome

Denys-Drash syndrome (DDS) is characterized by nephropathy, genital abnormalities, and predisposition to Wilms tumor. DDS is associated with constitutional WT1 mutations, the majority being missense mutations in the zinc-finger region. A dominant-negative mode of action of the mutant DDS proteins is thought to explain the more severe genitourinary phenotype seen in DDS compared with children with complete deletion of one WT1 allele. We present a phenotypically female child who presented with bilateral Wilms tumor at 8 months of age. She was found to have an XY karyotype and diagnosed with DDS. In the constitutional DNA of this child we found a previously unreported mutation in exon 1 of WT1. This de novo mutation, delT in codon 40, is predicted to produce a termination signal in codon 90 (F40fsX90). This frameshift mutation results in a severely truncated protein, which would remove both the zinc-finger DNA-binding domain and the majority of the N-terminal regulatory domain, including regions previously shown in vitro to be necessary for inhibition of WT1 transcriptional activity. Our results provide important physiological evidence that the first 40 amino acids of WT1 are capable of functionally important interactions, presumably through their ability to self-associate with full-length WT1.

Molecular and genetic regulation of testis descent and external genitalia development

Testicular descent as a prerequisite for the production of mature spermatozoa and normal external genitalia morphogenesis, and therefore facilitating copulation and internal fertilization, are essential developmental steps in reproduction of vertebrate species. Cryptorchidism, the failure of testis descent, and feminization of external genitalia in the male, usually in the form of hypospadias, in which the opening of the urethra occurs along the ventral aspect of the penis, are the most frequent pediatric complications. Thus, elucidating the molecular mechanisms involved in the regulation of testis descent and the formation of external genitalia merits a special focus. Natural and transgenic rodent models have demonstrated both morphogenic processes to be under the control of a plethora of genetic factors with complex time-, space-, and dose-restricted expression pattern. The review elucidates the molecular mechanisms involved in the regulation of testis descent and the formation of external genitalia and, wherever possible, assesses the differences between these rodent animal models and other mammalian species, including human.

The genetics of male undermasculinization

A review of the genetics of male undermasculinization must encompass a description of the embryology of the genital system. The dimorphism of sex development consequent upon the formation of a testis and the subsequent secretion of hormones to impose a male phenotype is highlighted. Thus, an understanding of the causes of male undermasculinization (manifest as XY sex reversal, complete and partial) includes reviewing the genetic factors which control testis determination and the production and action of testicular hormones. The study of disorders of male sex development has contributed substantially to knowledge of normal male development before birth. This knowledge has been complimented in recent years by the use of targeted murine gene disruption experiments to study the sex phenotype, although murine and human phenotypes are not always concordant. The investigation of disorders associated with male undermasculinization of prenatal onset is described briefly to complete the review.

The same mutation affecting the splicing of WT1 gene is present on Frasier syndrome patients with or without Wilms' tumor

Denys-Drash and Frasier syndromes are rare human disorders that associate nephropathy with gonadal and genital abnormalities. In DDS there is a predisposition to Wilms' tumor. Heterozygous point mutations in the Wilms' tumor, type1 gene (WT1), particularly those altering the zinc finger (ZF) encoding exons, have been reported in most DDS patients, while mutations in intron 9 of the same gene cause FS. This paper describes two cases of DDS, one FS and one patient with Wilm's tumor and intersex genitalia, in which mutations were searched by sequencing the exons 8 and 9 of WT1 gene. Patient 1 carried a missense point mutation in exon 8 (ZF2), converting a CGA-Arg codon to a TGA-stop codon. Patient 2 presented a single nucleotide deletion within exon 9 (ZF3) introducing a premature chain termination at codon 398. Patients 3 and 4 had a C-->T transition at position +4 of the second alternative splice donor site of exon 9 (this mutation was detected in peripheral blood and in tumor derived DNA of patient 3). However, patient 3 had previously developed a Wilms' tumor. This is the first case of Wilms' tumor development in a phenotypically and genetically confirmed case of FS.

A clinical overview of WT1 gene mutations

Mutations in the WT1 gene were anticipated to explain the genetic basis of the childhood kidney cancer, Wilms tumour (WT). Six years on, we review 100 reports of intragenic WT1 mutations and examine the accompanying clinical phenotypes. While only 5% of sporadic Wilms' tumours have intragenic WT1 mutations, > 90% of patients with the Denys-Drash syndrome (renal nephropathy, gonadal anomaly, predisposition to WT) carry constitutional intragenic WT1 mutations. WT1 mutations have also been reported in juvenile granulosa cell tumour, non-asbestos related mesothelioma, desmoplastic small round cell tumour and, most recently, acute myeloid leukemia.

Transcriptional regulation of PDGF-A and TGF-beta by +KTS WT1 deletion mutants and a mutant mimicking Denys-Drash syndrome

Denys-Drash syndrome (DDS) and Frasier syndrome (FS) are rare diseases caused by the mutations of Wilms tumor gene, WT1. The common denominator in these syndromes is a nephropathy which is manifested by early-onset proteinuria, nephrotic syndrome and end stage renal failure. Although these syndromes are genetic models of nephropathy and the mutations of WT1 gene are characterized in these patients the mechanism how mutations of WT1 gene affect the embryonic kidney adversely has not been elucidated. Recently, there was a report that FS is caused by mutations in the donor splice site of WT1. These mutations predicted loss of +KTS isoform, which is one of the four splicing variants of WT1. In this study, two +KTS deletion mutants of WT1 were made as well as a WT1 mutant mimicking a mutation found in a patient who had diffuse mesangial sclerosis, end stage renal failure and Wilms tumor. Mutant embryonic kidney cell lines were established by transfection of 293 embryonic kidney cells with WT1 mutants. We investigated the transcription regulation of mutant WT1 among these cell lines using the reporter vectors containing PDGF-A and TGF-beta promoter sequence. Our results showed that the promoter activity of PDGF-A and TGF-beta, which are related to the progression of glomerular diseases, was modestly increased in the mutant cell mimicking the patent, while those activities were markedly increased in other two deletion mutant cell lines. This study demonstrated that +KTS WT1 mutation found in DDS affected the cytokine expression adversely in vitro. From these results, we suggest that the alteration of +KTS WT1 expression be responsible for the rapid progression of renal diseases in DDS and FS.

Disorders of sexual differentiation

An infant born with ambiguous genitalia requires an accurate and prompt diagnosis so that a management plan can be formulated. This article discusses the signaling cascade of genes that controls sexual differentiation. Clinical disorders involving sex reversal or ambiguous genitalia are discussed in relation to the genes regulating sexual development. An approach to the treatment of these disorders is outlined.

Sex in the 90s: SRY and the switch to the male pathway

In mammals the male sex determination switch is controlled by a single gene on the Y chromosome, SRY. SRY encodes a protein with an HMG-like DNA-binding domain, which probably acts as a local organizer of chromatin structure. It is believed to regulate downstream genes in the sex determination cascade, although no direct targets of SRY are clearly known. More genes in the pathway have been isolated through mutation approaches in mouse and human. At least three genes, SRY itself, SOX9, and DAX1, are dosage sensitive, providing molecular evidence that the sex determination step operates at a critical threshold. SRY initiates development of a testis from the bipotential cells of the early gonad. The dimorphic male and female pathways present a rare opportunity to link a pivotal gene in development with morphogenetic mechanisms that operate to pattern an organ and the differentiation of its cells. Mechanisms of testis organogenesis triggered downstream of SRY include pathways of cell signaling controlling cell reorganization, cell proliferation, cell migration, and vascularization.

The Wilms' tumor 1 gene: oncogene or tumor suppressor gene?

The Wilms' tumor 1 (wt1) gene is one of at least three genes that are involved in the development of Wilms' tumor, a pediatric kidney cancer. The expression pattern of the gene indicates that wt1 not only plays a role during kidney development but is also involved in the development and homeostasis of several other tissues. The physiological function of the gene, however, remains to be elucidated. The gene products have been implicated in many processes like proliferation, differentiation, and programmed cell death (apoptosis). The WT1 proteins function as transcription factors but may additionally be involved in splicing. Disruption of these activities may lead to aberrant development. In this paper we will discuss the role of the wt1 gene during normal development and homeostasis of several tissues. In addition, we will address the involvement of the gene products in processes like apoptosis and tumorigenesis.

Genetic control of gonadal differentiation

The study of naturally occurring mutations in humans and induced mutations in mice that cause sex reversal has been instrumental in the cloning and functional analysis of genes involved in gonadal differentiation. Several genes required for this complex developmental process have now been identified. The genes LIM1, WT1 and FTZ-F1 have been demonstrated to be involved in the formation of the gonads prior to their differentiation as testes or ovaries. Subsequent sex-specific gonadal differentiation appears to be mediated by the SRY and SOX9 genes in the testis, and the DAX-1 gene in the ovary.

Software and database for the analysis of mutations in the human WT1 gene

The WT1 gene, located at 11p13, encodes a zinc finger transcription factor involved in renal and gonadal development and in Wilms' tumor. Constitutional mutations of this gene have been described in most patients with Denys Drash syndrome (mesangial sclerosis associated with male pseudohermaphrodism and/or Wilms' tumor), but also in patients with genitourinary abnormalities and Wilms' tumor (WT) or presenting with only unilateral or bilateral WT. Moreover, approximately 10% of Wilms' tumors carry WT1 mutations at the somatic level. To facilitate the genotype-phenotype correlation analyses, we have created a software package along with a computerized database of germline (70 entries) and somatic (28 entries) mutations reported in the literature.

Androgen insensitivity syndrome: a survey of diagnostic procedures and management in the UK

OBJECTIVE

A two year survey of androgen insensitivity syndrome (AIS) to assess current diagnostic and management strategies.

METHODS

Cases were ascertained by inclusion on the British Paediatric Surveillance Unit monthly report card for 24 months.

RESULTS

Fifty one of 139 notifications were confirmed as AIS; 29 cases were complete AIS and 22 cases partial AIS. Seventy six per cent of complete AIS presented with an inguinal hernia, and half the complete AIS patients had an established family history of the disorder. Presentation in the partial AIS group was through ambiguous or undermasculinised genitalia; 59% of partial AIS were raised as male.

CONCLUSIONS

The importance of karyotyping girls with inguinal hernias is confirmed, and further attention should be given to genetic counselling for families of complete AIS patients. A large number of cases were misreported as partial AIS, emphasising the importance of undertaking a comprehensive diagnostic evaluation in intersex states. A large percentage of children with partial AIS were raised as boys despite severe genital undermasculinisation, indicating the current lack of validated measures that predict genital response to androgen treatment. The management of AIS is discussed and diagnostic guidelines provided to improve the diagnostic yield in AIS.

Sex determination in humans

In mammals, the Y chromosome induces testis formation and thus male sexual development; in the absence of a Y chromosome, gonads differentiate into ovaries and female development ensues. Molecular genetic studies have identified the Y-located testis determining gene SRY as well as autosomal and X-linked genes necessary for gonadal development. The phenotypes resulting from mutation of these genes, together with their patterns of expression, provide the basis for establishing a hierarchy of genes and their interactions in the mammalian sex determination pathway.

Germline WT1 mutations in Wilms' tumor patients: preliminary results

We conducted a comparative study of the prevalence of germline WT1 mutations in patients with Wilms' tumor. Patients in Group 1 have familial Wilms' tumor, bilateral disease, associated urogenital anomalies, and/or second cancers. Those in Group 2 are unilateral, sporadic Wilms' patients without other associated conditions. Patients with aniridia or Denys-Drash syndrome are known to have WT1 alterations, and are excluded from this study. Preliminary results on 96 subjects show that the overall germline WT1 mutation frequency is low (< 5%). The work to date establishes the feasibility of identifying patients with germline WT1 mutations and, in the future, offering genetic predisposition testing to at-risk relatives. However, genetic predisposition testing of children for WT1 mutations raises many ethical, legal, and psychosocial issues; research is needed to evaluate risks and benefits.

No evidence of WT1 gene mutations in children with congenital diaphragmatic hernia

Children with congenital diaphragmatic hernia are born with a defect of the diaphragm that usually leads to a herniation of abdominal organs up into the thoracic cavity on the same side. The condition is often fatal, usually because of concomitant lung hypoplasia. The cause of this condition is unknown. The majority of cases are sporadic, but familial aggregation has been observed, indicating a genetic background. The tumor suppressor gene WT1 is involved in normal early urogenital development, and it is expressed in the mesothelium in the early human fetus. Recently, knockout mice homozygous for WT1 gene mutations were constructed. The embryos died between days 13 and 15 of gestation. Besides serious urogenital and thoracic malformations, the mice had defects in the diaphragm that caused herniation of lung tissue into the abdomen. These findings prompted the authors to screen for WT1 gene mutations in 27 children who had congenital diaphragmatic hernia. Using exon-per-exon polymerase chain reaction (PCR) amplifications and denaturing gradient gel electrophoresis, no WT1 mutations were detected. Southern blot analysis did not show any large rearrangements in the WT1 gene. These results exclude WT1 gene mutations as a major etiological factor for the isolated diaphragmatic defect. However, it is possible that other genes in the WT1 pathway are involved in this defect.

Down syndrome in association with features of the androgen insensitivity syndrome

Three cases of Down syndrome (DS) are reported in association with features of the androgen insensitivity syndrome (AIS). All were 47, XY, +21 and reared as females. One case had a normal female phenotype, and two cases showed minimal clitoromegaly and labial fusion. Minor genital underdevelopment has been reported as common in males with DS; however, AIS has not previously been associated with DS. Androgen binding studies in genital skin fibroblasts were normal in two cases and in the 46,XY brother of the third who has perineal hypospadias. Mutation screening of the androgen receptor (AR) gene by PCR-SSCP was normal in all cases. Normal androgen binding and the absence of an identified mutation in the coding region of the AR gene is very unusual in AIS, particularly in the complete form. This finding suggests the operation of hitherto unrecognised genes on chromosome 21 with a role in androgen response and sex differentiation.

Abnormal gonadal differentiation in two subjects with ambiguous genitalia, Mullerian structures, and normally developed testes: evidence for a defect in gonadal ridge development

Among a group of patients with abnormal sexual differentiation, we have identified two subjects who had a 46,XY karyotype, ambiguous genitalia, and well-developed Müllerian structures, but normal appearing testes. The presence of ambiguous genitalia and persistent Müllerian structures implied both Leydig cell and Sertoli cell dysfunction, hence, gonadal dysgenesis. However, the normal testicular histology suggested that the underlying abnormality was not a defect in testis determination itself but an abnormality in timing of gonadal ridge and testis development. In one of the two subjects genomic DNA was available. The sequence of the SRY gene was normal. Because rare patients with partial androgen insensitivity may have a similar phenotype, the AR gene was evaluated by denaturing gradient gel electrophoresis (DGGE) and was normal. Some subjects with mutation of the WT1 gene or with deletion of the distal short arm of chromosome 9 may have similar phenotypes. The WT1 gene was studied by single-strand conformation polymorphism (SSCP) analysis and was normal. In addition, there was no loss of heterozygosity of polymorphic markers in distal 9p. The gene for Müllerian inhibiting substance (MIS) was also studied by SSCP and was normal. Although the exact mechanism for the defect in the two subjects is unknown, it may be due to an abnormality in a gene or genes involved in the timing of gonadal ridge development.

Fluorescence-based mutation detection. Single-strand conformation polymorphism analysis (F-SSCP)

Conventional SSCP analysis of DNA amplified by polymerase chain reaction (PCR-SSCP) is one of the simplest and most reliable tools for identifying point mutations, and small insertions or deletions. The sensitivity of the technique is increased by using the Applied Biosystems (ABI) semiautomated DNA sequencer equipped with GENESCAN 672 software for F-SSCP. The four-dye ABI system permits a red dye-labeled internal lane standard to be run in the same lanes as the DNA being examined, leaving three dye colors for labeling DNA of interest. The internal lane standard is used to normalize gels or correct for minor differences in apparent electrophoretic mobility between lanes. Correction for these lane-dependent differences in migration and the capability to stack data from two different lanes on the computer screen makes it possible to detect sequence variants that produce very small mobility shifts. Coelectrophoresis of control and unknown DNA in the same lane, using different dye labels for each, is also helpful for detecting sequence variants that produce small mobility changes. Multiplexing multiple F-SSCP targets in the same lane increases sample throughput.

Absence of mutations in the WT1 gene in patients with XY gonadal dysgenesis

The WT1 gene is normally expressed during gonadal development and specific mutations in heterozygous form cause Drash syndrome, characterized by male pseudohermaphroditism and gonadal dysgenesis, renal failure and a predisposition for Wilms' tumour. These observations prompted us to test whether WT1 mutations are involved in isolated gonadal dysgenesis, being the most severe form of disturbance in gonadal differentiation. We studied 27 cases of 46,XY females with gonadal dysgenesis who had previously been screened for and found not to carry SRY gene mutations. We performed mutational screening of the WT1 gene with denaturing gradient gel electrophoresis. In one of these patients, a heterozygous point mutation in exon 8 was found. This mutation has previously been described in Drash syndrome and re-evaluation of the clinical data confirmed this diagnosis. Based on these results, we conclude that isolated gonadal dysgenesis is not caused by mutations in the WT1 gene.

The Denys-Drash syndrome

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Androgen insensitivity syndrome

In a relatively short period of time, understanding of the fundamental causes of androgen insensitivity syndromes has improved dramatically. This has been brought about by the combination of several disciplines, including endocrinology, genetics, developmental and molecular biology. Mutations can be identified in the androgen receptor gene in suspected cases of AIS, and their functional consequences examined in various in-vitro systems. This information can then be correlated with the clinical presentation of the patient, and is beginning to provide an explanation for the highly variable clinical presentation of AIS. It is to be hoped that this information will also help to predict the likely outcome of androgen therapy in infants with PAIS and an intersex phenotype. More speculatively, functional studies may also lead to novel strategies for the treatment of patients. This would then be of enormous benefit to both patient and parents. Furthermore, the identification of a mutation allows precise information for genetic counselling of families affected by AIS. However, many questions still remain to challenge clinicians and scientists alike. These include the risk of testicular malignancy in patients with AIS and currently there is no worldwide consensus on the stage at which testes should be removed from patients reared as female. There are also significant challenges in patient counselling. Although there is greater understanding of the molecular defects that cause AIS, there are several examples of patients with a similar degree of receptor dysfunction, or even the same mutation, but whose phenotypes are widely different. Other factors must therefore contribute to the clinical presentation of AIS, although these have not been identified. Finally, there are the mutations in patients with Kennedy's disease. The consequences of the mutations are unexplained and are a clear indication that there is still a great deal to discover about the function and biology of androgen receptors.