Testicular development in an SRY-negative 46,XX individual harboring a distal Xp deletion

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.

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.

Sex determination and the Y chromosome

Although SRY was first identified 10 years ago, we still know remarkably little about its mode of action or downstream target genes. Recently, potential protein partners have been identified and there has been considerable activity to understand the roles of WT1, SF-1, DAX-1 and SOX9 in gonadogenesis. The emerging picture is one of complex interactions, involving both positive and negative regulatory signals that, depending on the cellular and promoter context, drive the expression of male-specific genes. Despite recent advances, however, we are still unable to explain the genetic cause of most cases of 46,XY gonadal dysgenesis or even a single case of Y-chromosome-negative 46,XX maleness.

An apparent excess of sex- and reproduction-related genes on the human X chromosome

We describe here the results of a search of Mendelian inheritance in man, GENDIAG and other sources which suggest that, in comparison with autosomes 1, 2, 3, 4 and 11, the X chromosome may contain a significantly higher number of sex- and reproduction-related (SRR) genes. A similar comparison between X-linked entries and a subset of randomly chosen entries from the remaining autosomes also indicates an excess of genes on the X chromosome with one or more mutations affecting sex determination (e.g. DAX1), sexual differentiation (e.g. androgen receptor) or reproduction (e.g. POF1). A possible reason for disproportionate occurrence of such genes on the X chromosome could be that, during evolution, the 'choice' of a particular pair of homomorphic chromosomes for specialization as sex chromosomes may be related to the number of such genes initially present in it or, since sex determination and sexual dimorphism are often gene dose-dependent processes, the number of such genes necessary to be regulated in a dose-dependent manner. Further analysis of these data shows that XAR, the region which has been added on to the short arm of the X chromosome subsequent to eutherian-marsupial divergence, has nearly as high a proportion of SRR genes as XCR, the conserved region of the X chromosome. These observations are consistent with current hypotheses on the evolution of sexually antagonistic traits on sex chromosomes and suggest that both XCR and XAR may have accumulated SRR traits relatively rapidly because of X linkage.

Regulation of sexual dimorphism in mammals

Sexual dimorphism in humans has been the subject of wonder for centuries. In 355 BC, Aristotle postulated that sexual dimorphism arose from differences in the heat of semen at the time of copulation. In his scheme, hot semen generated males, whereas cold semen made females (Jacquart, D., and C. Thomasset. Sexuality and Medicine in the Middle Ages, 1988). In medieval times, there was great controversy about the existence of a female pope, who may have in fact had an intersex phenotype (New, M. I., and E. S. Kitzinger. J. Clin. Endocrinol. Metab. 76: 3-13, 1993.). Recent years have seen a resurgence of interest in mechanisms controlling sexual differentiation in mammals. Sex differentiation relies on establishment of chromosomal sex at fertilization, followed by the differentiation of gonads, and ultimately the establishment of phenotypic sex in its final form at puberty. Each event in sex determination depends on the preceding event, and normally, chromosomal, gonadal, and somatic sex all agree. There are, however, instances where chromosomal, gonadal, or somatic sex do not agree, and sexual differentiation is ambiguous, with male and female characteristics combined in a single individual. In humans, well-characterized patients are 46, XY women who have the syndrome of pure gonadal dysgenesis, and a subset of true hermaphrodites are phenotypic men with a 46, XX karyotype. Analysis of such individuals has permitted identification of some of the molecules involved in sex determination, including SRY (sex-determining region Y gene), which is a Y chromosomal gene fulfilling the genetic and conceptual requirements of a testis-determining factor. The purpose of this review is to summarize the molecular basis for syndromes of sexual ambiguity seen in human patients and to identify areas where further research is needed. Understanding how sex-specific gene activity is orchestrated may provide insight into the molecular basis of other cell fate decisions during development which, in turn, may lead to an understanding of aberrant cell fate decisions made in patients with birth defects and during neoplastic change.

An autosomal or X linked mutation results in true hermaphrodites and 46,XX males in the same family

It is now well established that the differentiation of the primitive gonad into the testis during early human embryonic development depends on the presence of the SRY gene. However, the existence of total or partial sex reversal in 46,XX males with genetic mutations not linked to the Y chromosome suggests that several autosomal genes acting in association with SRY may contribute to normal development of the male phenotype. We report a family in which four related 46,XX subjects with no evidence of Y chromosome DNA sequences underwent variable degrees of male sexual differentiation. One 46,XX male had apparently normal male external genitalia whereas his brother and two cousins had various degrees of sexual ambiguity and were found to be 46,XX true hermaphrodites. The presence of male sexual development in genetic females with transmission through normal male and female parents indicates that the critical genetic defect is most likely to be an autosomal dominant mutation, the different phenotypic effects arising from variable penetrance. Other autosomal loci have been implicated in male sexual development but the genetic mechanisms involved are unknown. In this family there may be an "activating" mutation which mimics the initiating role of the SRY gene in 46,XX subjects.