Genomic imprinting and Wilms' tumor

The selective loss of maternal and reduplication of paternal chromosome 11p15.5 alleles in Wilms' tumors (WTs) points to the existence of a paternally imprinted tumor suppressor gene(s) and/or a maternally imprinted dose-dependent growth-promoting gene(s) in this chromosomal region. Two reciprocally imprinted chromosome 11p15.5 genes, H19, a candidate tumor suppressor gene, and IGF2, a candidate dominant oncogene, have been well-characterized in terms of their imprinting and expression status in WTs. Here we review and extend data indicating that a majority of WTs show a bipaternal epigenotype at these loci, with H19 inactive and IGF2 biallelically active. This can arise either through loss of heterozygosity (LOH) or by a non-LOH pathway involving localized biallelic hypermethylation of H19DNA. Conversion to this bipaternal endpoint has recently been found to affect not only these two genes, but also at least one other imprinted 11p15.5 gene, KIP2. Since 11p15.5 LOH and biallelic H19 hypermethylation can occur both early and late in tumor progression and since early loss is not associated with bilaterality or multifocality of WTs, these types of lesions appear to be permissive rather than rate-limiting in Wilms' tumorigenesis. © 1996 Wiley-Liss, Inc.     

A novel missense mutation in the EVC gene underlies Ellis‐van Creveld syndrome in a Pakistani family

Background: Ellis‐van Creveld (EVC) syndrome is a rare autosomal recessive disorder characterized by skeletal, ectodermal and cardiac defects. This syndrome is caused by mutations in EVC and EVC2 genes, which are separated by 2.6 kb of genomic sequence on chromosome 4p16. Methods: In the present study we ascertained a four‐generation pedigree of Pakistani origin with features of EVC. Linkage was searched by genotyping microsatellite markers linked to chromosome 4p16. Affected individuals showed homozygosity to the microsatellite markers tightly linked to EVC and EVC2 genes on chromosome 4p16. It was then subjected to direct sequencing of the EVC and EVC2 genes. Results: Mutation analysis of the EVC and EVC2 genes identified a novel missense change (c.617G>A; p.S206N) in the EVC gene. Conclusions: We herein report on the first family from Pakistan with a large number of individuals affected by EVC. DNA sequence analysis led to the identification of the fifth missense mutation in the EVC gene.     

A del(X)(p11) carrying SRY sequences in an infant with ambiguous genitalia

Background  

SRY (sex-determining region, Y) is the gene responsible of gonadal differentiation in the male and it is essential for the regular development of male genitalia. Translocations involving the human sex chromosomes are rarely reported, however here we are reporting a very rare translocation of SRY gene to the q -arm of a deleted X chromosome. This finding was confirmed by cytogenetic, fluorescent in situ hybridization (FISH) and polymerase chain reaction (PCR).     

Mutations in SOX9 cause both autosomal sex reversal and campomelic dysplasia

The human testis determining factor (SRY) has been cloned from the Y chromosome. This gene is a dominant inducer of male differentiation. Mutations in the SRY gene result in an XY individual developing as a sex reversed phenotypic female. Sex reversal in humans can also be caused by mutations located in autosomal or X-linked loci. One such sex-reversing locus (SRAI) is associated with the developmental disorder campomelic dysplasia (CD). Both these syndromes were mapped to human chromosome 17q by the identification of balanced reciprocal translocations in five unrelated patients. The translocation breakpoint of one such XY-female CD patient was mapped and the region surrounding it cloned. The closest distal marker used to map the translocation breakpoint was the SOX9 gene. Because of the close proximity of this gene to the breakpoint, it was subjected to mutation analysis in patients without overt chromosome rearrangements. Analysis of DNA from these patients and their parents identified de novo mutations in the SOX9 gene in patients with both autosomal sex reversal and CD. This showed that mutations in the SOX9 gene are responsible for both syndromes.     

Epigenetic abnormality of SRY gene in the adult XY female with pericentric inversion of the Y chromosome

In normal ontogenetic development, the expression of the sex‐determining region of the Y chromosome (SRY) gene, involved in the first step of male sex differentiation, is spatiotemporally regulated in an elaborate fashion. SRY is expressed in germ cells and Sertoli cells in adult testes. However, only few reports have focused on the expressions of SRY and the other sex‐determining genes in both the classical organ developing through these genes (gonad) and the peripheral tissue (skin) of adult XY females. In this study, we examined the gonadal tissue and fibroblasts of a 17‐year‐old woman suspected of having disorders of sexual differentiation by cytogenetic, histological, and molecular analyses. The patient was found to have the 46,X,inv(Y)(p11.2q11.2) karyotype and streak gonads with abnormally prolonged SRY expression. The sex‐determining gene expressions in the patient‐derived fibroblasts were significantly changed relative to those from a normal male. Further, the acetylated histone H3 levels in the SRY region were significantly high relative to those of the normal male. As SRY is epistatic in the sex‐determination pathway, the prolonged SRY expression possibly induced a destabilizing effect on the expressions of the downstream sex‐determining genes. Collectively, alterations in the sex‐determining gene expressions persisted in association with disorders of sexual differentiation not only in the streak gonads but also in the skin of the patient. The findings suggest that correct regulation of SRY expression is crucial for normal male sex differentiation, even if SRY is translated normally.     

Clinical and behavioural profile of a rare variant of Klinefelter syndrome-48, XXXY

Klinefelter’s syndrome is a sex chromosomal aneuploidy caused by an addition of X chromosome in males (47,XXY).Variants of this syndrome with X and Y polygamy are of rare occurrence. Here we describe a rare case of 48, XXXY Klinefelter’s variant from South India with a reported incidence of 1 per 17,000 to 1 per 50,000 male births. The presence of an extra X chromosome/s in these individuals has a great impact on the physical and cognitive functions, which could be attributed to gene dosage effects and genes involved in neurogenic development.     

Deletion of the long arm of the Y chromosome in an adolescent with short stature and hypogonadism

We describe a patient with short stature more than that expected for non-treated congenital adrenal hyperplasia due to nonclassic 21-hydroxylase deficiency with deletions in the long arm of the Y chromosome including the CGY gene and the AZF subregions.     

Global gene profiling and comprehensive bioinformatics analysis of a 46,XY female with pericentric inversion of the Y chromosome

XY females are rare individuals who carry a Y chromosome but are phenotypically female. In approximately 80–90% of these cases, there are no mutations in the SRY gene, a testis-determining gene on the short arm of the Y chromosome, and the pathophysiology of XY females without SRY mutation remains unclear. In the present study, we used a molecular data mining technique to analyze the pathophysiology of an XY female with functional SRY and pericentric inversion of the Y chromosome, and compared the results with those of a normal male. Interestingly, upregulations of numerous genes included in the development category of the Biological Process ontology, including genes associated with sex determination and organ morphogenesis, were seen in the patient. Additionally, the transforming growth factor-β (TGF-β) signaling pathway and Wnt signaling pathway, in which most cell–cell interactions during embryonic development are involved, were altered. Alterations in the expression of numerous genes at the developmental stage, including alterations at both the gene and pathway levels, may persist as a vestige of anomalies of sex differentiation that presumably began in the fetal period. The present study indicates that a data mining technique using bioinformatics contributes to identification of not only genes responsible for birth defects, but also disorders of sex development (DSD)-specific pathways, and that this kind of analysis is an important tool for clarifying the pathophysiology of human idiopathic XY gonadal dysgenesis. Our findings could serve as one of the basic datasets which will be used for future follow-up investigations.     

Prenatal molecular diagnosis of X‐linked hydrocephalus via a silent C924T mutation in the L1CAM gene

We present a case of a patient whose L1CAM gene in X‐chromosome has a C924T transition. Her first son's ventriculomegaly was prenatally detected. A mature infant was born, his head circumference was large, and thumbs were bilaterally adducted. X‐linked hydrocephalus (XLH) was suspected. The DNA examination revealed that both her and boy's LICAM gene had a C924T transition. She became pregnant 5 years later and amniocentesis was performed. The results of cytogenetic analysis revealed that the fetus was female. She continued her pregnancy and delivered a healthy girl. She again became pregnant 3 years later. The chromosomal analysis revealed that the fetus was male. Fetal DNA analysis determined that the fetus had the inherited mutation. She chose to terminate the pregnancy. A C924T mutation can be disease causing for XLH, and the detection of this mutation would aid in genetic counseling for the prenatal diagnosis of XLH.     

Tuberous Sclerosis: Diagnosis and Prenatal Diagnosis by MLPA

Tuberous sclerosis complex (TSC) is an autosomal dominant disorder, caused due to mutations in the TSC1 and TSC2 genes. Mutations in TSC2 gene are more common than in TSC1 gene and mostly they are in the form of large genomic deletions or duplications. The authors report on a novel deletion in TSC2 gene, prenatal diagnosis and genetic counseling in a family with a 3- year- old affected male child. This is the first report on MLPA based mutation analysis of TSC1 and TSC2 genes from India.     

Linkage analysis and identification of deletion in Alagille syndrome gene

Alagille syndrome (AGS) is a genetic disease and the responsible gene has already been mapped at 20p12. To more accurately detect the region of the AGS gene on the linkage map of chromosome 20p, 14 yeast artificial chromosome (YAC) clones were screened to construct a YAC contig in the candidate region and 13 locus markers and 2 sequence-tagged sites (STS) were ordered. Combining all of the analyses, a 1.3 Mb critical region from D20S507 to D20S61 for the AGS gene was identified. As the human Jagged 1 gene (JAGI) lies just in this region and is responsible for the AGS disease, the genomic DNA in an AGS family without a visible deletion were analyzed by single-strand conformational polymorphism (SSCP) and direct DNA sequencing, and a 2-bp (CT) deletion mutation at exon 26 of the JAGI was identified.     

No Evidence for Angiotensin Type 2 Receptor Gene Polymorphism in Intron 1 in Patients with Coarctation of the Aorta and Ullrich–Turner Syndrome

In male patients with congenital anomalies of the kidney and urinary tract, an increased incidence of a polymorphism in the angiotensin type 2 receptor gene (AT2R) has been identified. The AT2R has been shown to be involved in apoptosis, particularly during embryogenesis. The aim of this study was to examine the A→1675G transition polymorphism in intron 1 of the AT2R gene that is located on the X chromosome in patients with coarctation of the aorta (CoA) with and without Ullrich–Turner syndrome (UTS). Screening of DNA samples was performed with restriction fragment length polymorphism analysis. Ninety-seven patients with CoA, 28 girls with UTS, 10 girls with UTS and CoA, and 96 control individuals were studied. There was no significant difference in the distribution of A and G-genotypes in any of the patient groups compared to controls. An A→1675G transition in the AT2R gene seems not to be involved in the pathogenesis of aortic coarctation.     

Sex determining gene on the X chromosome short arm: Dosage sensitive sex reversal

The present review article summarizes current knowledge concerning the sex determining gene on Xp21, termed DSS (dosage sensitive sex reversal). The presence of DSS has been based on the finding that, in the presence of SRY, partial active Xp duplications encompassing the middle part of Xp result in sex reversal, whereas those of the distal or proximal part of Xp permit male sex development. Because Klinefelter patients develop as males, it is believed that DSS is normally subject to X-inactivation, and that two active copies of DSS override the function of SRY, resulting in gonadal dysgenesis because of meiotic pairing failure. It may be possible that DSS encodes a target sequence for repressing function of SRY or that DSS is involved in an X chromosome-counting mechanism. Molecular approaches have localized DSS to a 160 kb region and isolated candidate genes such as DAX-1 and MAGE-Xp, but there has been no formal evidence equating the candidate gene with DSS. In addition to its clinical importance, the exploration of DSS must provide a useful clue to phylogenetic studies of sex chromosomes and dosage compensation.     

Gene targeting in kidney development

Cancer and development are conceptually related because tumor formation in many cases results from the aberrant expression of a developmental program. This is certainly true of Wilms' tumors, which display a range of phenotypes resembling various stages of kidney development. WT1 has been identified as a tumor suppressor gene involved in a subset of Wilms' tumors. Gene targeting of the WT1 gene demonstrated the requirement for this gene product during early urogenital development. Several other genes, including Wnt-4, c-ret, Id and lim 1, have been shown by gene targeting to also be involved in early kidney development. This review discusses gene targeting as an approach to the study of development and reviews the phenotypes of these and other genes involved in kidney organogenesis. © 1996 Wiley-Liss, Inc.     

Clinical, hormonal and cytogenetic evaluation of 46,XX males and review of the literature

The main factor influencing the sex determination of an embryo is the genetic sex determined by the presence or absence of the Y chromosome. However, some individuals carry a Y chromosome but are phenotypically female (46,XY females) or have a female karyotype but are phenotypically male (46,XX males). 46,XX maleness is a rare sex reversal syndrome affecting 1 in 20,000 newborn males. Molecular analysis of sex-reversed patients led to the discovery of the SRY gene (sex-determining region on Y). The presence of SRY causes the bipotential gonad to develop into a testis. The majority of 46, SRY-positive XX males have normal genitalia; in contrast SRY-negative XX males usually have genital ambiguity. A small number of SRY-positive XX males also present with ambiguous genitalia. Phenotypic variability observed in 46,XX sex reversed patients cannot be explained only by the presence or absence of SRY despite the fact that SRY is considered to be the major regulatory factor for testis determination. There must be some other genes either in the Y or other autosomal chromosomes involved in the definition of phenotype. In this article, we evaluate four patients with 46,XX male syndrome with various phenotypes. Two of these cases are among the first reported to be diagnosed prenatally.     

13q33.2 deletion: a rare cause of ambiguous genitalia in a male newborn with growth restriction

13q deletion is a rare cause of ambiguous genitalia in the male newborn, and can be associated with mental retardation of varying degree, retinoblastoma, and malformations of the brain, eye, genitourinary and gastrointestinal tract, depending on the level of the deletion. We present a male neonate with ambiguous genitalia and IUGR with a 13q33.2 deletion, and a paternal balanced translocation. Microarray analysis found the genes involved to be on chromosome 13 in the region 102989254bp–109214509bp. This deletion encompasses the EFNB2 gene, which has been implicated in genital malformations in 13q deletion cases. Conclusions: We find a link between haploinsufficiency of the EFNB2 gene and the presence of ambiguous genitalia and hypospadia in patients with a 13q.33 deletion. This work emphasizes the importance of early diagnosis of this condition due to the link with mental retardation and the need for follow up and management.     

Alopecia congenita universalis,microcephaly, cutis marmorata,short stature and XY gonadal dysgenesis: variable expression of El-Shanti syndrome

Alopecia congenita, laryngomalacia, and XY gonadal dysgenesis has been reported recently as a new syndrome in two unrelated Arab families from Jordan. We report a 4-year-old girl of first cousin Arab parents who had alopecia, microcephaly, cutis marmorata, short stature and borderline cognitive development. Karyotype analysis revealed a male constitution (46,XY) with no deletion of STS or SRY. She showed entirely normal female external genitalia and absence of female internal genitalia. Histological examination of the very small testicles found on laparascopy showed developed spermatic cords and paratesticular tissue with no testicular parenchyma, no Sertoli or Leydig cell development, and no seminiferous tubular development. Hormonal profile was that of a normal female child. Southern blotting and PCR assays showed an intact Y chromosome. Limited sequencing of the SRY gene revealed no mutations. Conclusion: this patient, together with the recently reported consanguineous families, represent a previously unrecognised autosomal recessive trait with pleiotropic effects including XY gonadal dysgenesis.     

Practical approach to steroid 5alpha-reductase type 2 deficiency

The aim of this article is to review the literature on steroid 5alpha-reductase type 2 deficiency (5α-RD2) to provide clinicians with information to guide their management of patients with this disorder. The 5alpha-reductase type 2 is encoded by the 5alpha-reductase type 2 gene (SRD5A2) on chromosome 2 and is predominantly expressed in external genital tissues and the prostate. Mutations of the SRD5A2 gene leads to an uncommon autosomal recessive disorder affecting sexual differentiation in individuals with 46,XY karyotype; their phenotype can range from almost normal female structures to a distinct male phenotype with ambiguous genitalia at birth. These phenotypes result from impaired conversion of testosterone to dihydrotestosterone due to mutations in the SRD5A2 gene. Patients exhibit virilization at puberty without breast development, which is often accompanied by gender identity change from female to male. More than 40 mutations have been reported in all five exons of the SRD5A2 gene. Phenotype–genotype correlations for 5α-RD2 have not been well established. The newborn phenotypes of male pseudohermaphrodites with 5α-RD2, partial androgen insensitivity syndrome (PAIS), or 17β-hydroxysteroid dehydrogenase type 3 (17β-HSD3) enzyme deficiency may be indistinguishable. We conclude that steroid 5α-RD2 should be included in the differential diagnosis of newborns with 46,XY DSD. It is important that the diagnosis be made in infancy by biochemical and molecular studies before gender assignment or any surgical intervention because these patients should be considered males at birth.