A novel nonsense mutation in the HMG box of the SRY gene in a patient with XY sex reversal

The clinical analysis of small supernumerary marker chromosomes in 17 children with mos 45,X/46,X,+mar karyotype

Small supernumerary maker chromosome (sSMC) is a type of structurally abnormal chromosome. In order to identify the origin, morphology and other characteristics of sSMCs in children with mos 45,X/46,X,+mar karyotype, 17 patients (16 females and 1 male) were analyzed. All patients underwent general physical examination, gonadal imaging and molecular cytogenetic analyses, including Giemsa banding, dual-color fluorescence in situ hybridization and detection of the sex-determining region Y gene by polymerase chain reaction. Cytogenetic analyses indicated sSMCs in 14/17 cases were derived from the X chromosome, of which 8 individuals presented with ring-shaped sSMCs and 6 with centric minute-shaped sSMCs. The remaining 3 cases were derived from the Y chromosome, and all presented with minute-shaped sSMCs. All female patients exhibited short stature, gonadal dysgenesis and other typical features of Turner syndrome. The male patient exhibited short stature, hypospadias and bilateral cryptorchidism. In conclusion, the majority of the sSMCs in patients with a mos 45,X/46,X,+mar karyotype were derived from the sex chromosomes. The molecular cytogenetic features of sSMCs may provide useful information for genetic counseling, prenatal diagnosis and individualized treatment.

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-beta (TGF-beta) 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.

Mechanisms of disease: Transcription factors in sex determination--relevance to human disorders of sex development

Sex determination is the series of molecular events that direct the undifferentiated bipotential gonad to become either a testis or an ovary. In humans, disruption of this process results in intersexuality, also referred to as disorders of sex development (DSD). Despite the discovery of the sex-determining gene SRY (sex-determining region Y) 15 years ago, the molecular mechanisms of sex determination remain poorly understood. Analysis of clinically relevant mutations of sex-determining genes in individuals with DSD has provided considerable insight into the function of these genes. The majority of disorders of sex determination with known causes are explained by mutations in one of three transcription factors at the core of the sex-determining pathway: SRY, SOX9 (SRY-box 9) and NR5A1 (nuclear receptor subfamily 5, group A, member 1). These mutations either affect the level of protein available at its nuclear site of action (via changes in regulatory sequences, deletions, non-sense mutations or mutations in nuclear localization sequences), or alter the structure of the protein (via modifications of binding or bending activity, or of interactions with other proteins). Deciphering the functional diversity of the mutations affecting the sex-determining pathway has immediate clinical impact on the diagnosis, outcome studies and classification of patients with DSD.

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).

Case presentation

A 7-month infant was clinically diagnosed as an intersex case, with a phallus, labia majora and minora, a blind vagina and a male urethra. Neither uterus nor testes was detected by Ultrasonography. G-banding of his chromosomes showed 46,X,del(X)(p11) and fluorescent in situ hybridization (FISH) analysis showed a very small piece from the Y chromosome translocated to the q-arm of the del(X). Polymerase chain reaction (PCR) analysis revealed the presence of material from the sex-determining region Y (SRY) gene.

Conclusion

It is suggested that the phenotype of the patient was caused by activation of the deleted X chromosome with SRY translocation, which is responsible for gonadal differentiation.

Identification of a new nonsense mutation (Tyr129Stop) of the SRY gene in a newborn infant with XY sex-reversal

Point mutations and deletions of SRY gene have been described in several cases of XY gonadal dysgenesis. To date, most of these mutations affect the HMG domain of SRY which plays a central role in DNA binding activity of SRY. We report on a non-mosaic XY sex-reversed newborn girl (completely female external genitalia). The direct sequencing of SRY showed a new nonsense mutation in a codon of SRY gene flanking the 3' end of the HMG domain: a thymine is replaced by a guanine at position +387 in codon 129, resulting in the replacement of the amino acid tyrosine (TAT) by a stop codon (TAG). The new mutation of this patient provides further evidence to support the functional importance of the putative DNA binding activity of the HMG-box domain.

Molecular dissection of the human Y-chromosome

Human Y chromosome, earlier thought to be gene deficient, has attracted a great deal of attention owing to its supremacy in male sex determination and unique haplotype status in the genome. Studies on Y chromosome have shown the presence of different types of satellite DNA and several genes implicated with a variety of physical and physiological functions. The interaction of these repetitive DNA with genes in normal individuals and in patients with Y-chromosome-related genetic anomalies is still an unresolved issue and is actively being pursued. The fast changing scenario of the human genome project is likely to effect our overall understanding of the Y chromosome and Y-linked genetic anomalies in a big way. We provide a brief overview of the organization of Y chromosome with respect to several important loci encompassing both the arms and their likely involvement/modulation in genetic anomalies. The experimental approaches discussed here are envisaged to be of clinical relevance for the molecular diagnosis of the Y-linked disorders.

Sry, Sox9 and mammalian sex determination

Sry is the Y-chromosomal gene that acts as a trigger for male development in mammalian embryos. This gene encodes a high mobility group (HMG) box transcription factor that is known to bind to specific target sequences in DNA and to cause a bend in the chromatin. DNA bending appears to be part of the mechanism by which Sry influences transcription of genes downstream in a cascade of gene regulation leading to maleness, but the factors that cooperate with, and the direct targets of, Sry remain to be identified. One gene known to be downstream from Sry in this cascade in Sox9, which encodes a transcription factor related to Sry by the HMG box. Like Sry, mutations in Sox9 disrupt male development, but unlike Sry, the role of Sox9 is not limited to mammals. This review focuses on what is known about the two genes and their likely modes of action, and draws together recent data relating to how they might interconnect with the network of gene activity implicated in testis determination in mammals.

An SRY-negative XX male with Huriez syndrome

This report studies a 42-year-old 46,XX patient affected by palmoplantar keratoderma. clinically classified as Huriez syndrome. The patient showed a male phenotype with apparently normal male features including testicular development. Cytogenetic and chromosomal painting analysis excluded the presence of translocation of the Y chromosome. PCR analysis of genomic DNA failed to detect the presence of the testis-determining gene, SRY. The presence of other Y-chromosome genes, known to be involved in testicular maturation and spermatogenesis, has also been analyzed. The data suggest that the sex reversal in this 46,XX male patient is due to a defect on a yet unidentified autosomal or X-linked sex-determining gene. The relationship between the sex reversion and the presence of sclerotylosis is discussed.

Naturally occurring mutants of human steroid 21-hydroxylase (P450c21) pinpoint residues important for enzyme activity and stability

Three mutants (deletion of E196, G291S, and R483P) of steroid 21-hydroxylase (P450c21) from patients with inherited congenital adrenal hyperplasia had reduced activity toward progesterone and 17-hydroxyprogesterone after transient expression in cultured mammalian cells. In addition, both the E196 deletion and the R483P mutant had shorter half-lives than the wild-type enzyme, whereas the half-life of the G291S mutant was comparable with that of the normal protein. These results directly link the clinical situation with the three mutations and suggest that G291 is important for the catalytic activity of P450c21.

The role of SRY in mammalian sex determination

The gene SRY (sex determining region of the Y), located at the distal region of the short arm of the Y chromosome, is necessary for male sex determination in mammals. SRY initiates the cascade of steps necessary to form a testis from an undifferentiated gonad. The SRY gene encodes an HMG (High Mobility Group) protein which may act as a transcription factor by binding to double stranded DNA and then bending the DNA. Mutations in SRY have been identified in some subjects with 46,XY pure gonadal dysgenesis. However the role for other autosomal and X-linked genes in testis determination is evident by the presence of a normal SRY gene in the majority of females with 46,XY pure gonadal dysgenesis and the lack of SRY in a minority of males with 46,XY maleness.