Evidence of XX-XY sex chromosome mosaicism in a child with true hermaphroditism

Natural human chimeras: A review

The term chimera has been borrowed from Greek mythology and has a long history of use in biology and genetics. A chimera is an organism whose cells are derived from two or more zygotes. Recipients of tissue and organ transplants are artificial chimeras. This review concerns natural human chimeras. The first human chimera was reported in 1953. Natural chimeras can arise in various ways. Fetal and maternal cells can cross the placental barrier so that both mother and child may become microchimeras. Two zygotes can fuse together during an early embryonic stage to form a fusion chimera. Most chimeras remain undetected, especially if both zygotes are of the same genetic sex. Many are discovered accidently, for example, during a routine blood group test. Even sex-discordant chimeras can have a normal male or female phenotype. Only 28 of the 50 individuals with a 46,XX/46,XY karyotype were either true hermaphrodites or had ambiguous genitalia. Blood chimeras are formed by blood transfusion between dizygotic twins via the shared placenta and are more common than was once assumed. In marmoset monkey twins the exchange via the placenta is not limited to blood but can involve other tissues, including germ cells. To date there are no examples in humans of twin chimeras involving germ cells. If human chimeras are more common than hitherto thought there could be many medical, social, forensic, and legal implications. More multidisciplinary research is required for a better understanding of this fascinating subject.

XX/XY chimerism encountered during prenatal diagnosis

46,XX/46,XY chimerism has previously been reported in patients with abnormal sexual development, and rarely in otherwise normal individuals. We report the first postnatally documented prenatal diagnosis of whole-body 46,XX/46,XY chimerism in humans, discovered by maternal age amniocentesis. The normal male phenotype in this child creates a dilemma in prenatal counselling, since genotypic male/female chimerism cannot be assumed to imply an abnormal sexual phenotype.

Unilateral true hermaphrodite with 46,XX/46,XY dispermic chimerism

A 13 year old female presented with ambiguous external genitalia, right inguinal ovotestis, left ovary, apparently normal Mullerian system, and absent Wolffian system. Cultured lymphocytes showed a 46,XX/46,XY karyotype. Histopathology of the gonads confirmed true hermaphroditism. The presence of two genetically different erythrocyte populations was observed. The findings suggested that the patient is a true hermaphrodite dispermic chimera.

A true hermaphrodite dispermic chimera with 46,XX and 46,XY karyotypes

A 16-year-old male with hypospadias and gynaecomastia had a rudimentary uterus with a right Fallopian tube and ovary; the left gonad was a functioning testis. Cytogenetic studies showed cells with 46,XX and 46,XY sex chromosomes in cultured blood, skin and gonadal tissues. Cells with the 46,XX constitution predominated in all tissues. Extensive investigations failed to demonstrate blood cell and serum chimerism, but there was little genetic variation of these characters between family members. Cytogenetic studies demonstrated that the father had contributed different marker chromosomes to the 46,XY and 46,XX cell lines of the propositus, whereas the mother had contributed the same two informative markers to both cell lines. The patient was a chimera with two diploid cell lines of different sex that had developed from the products of two separate acts of syngamy. Dispermy was demonstrated, and, whereas there was no evidence of different maternal contributions to the chimeric cell lines, uncertainty remains that these were identical.

True hermaphroditism with XX/XY sex chromosome mosaicism: report of a case

A case of true hermaphroditism with 46, XX/46, XY karyotype is reported. The propositus, reared as a male, showed ambiguous external genitalia with perineoscrotal hypospadias, and internal genitalia represented by bilateral ovotestes, normal uterus and tubes. Periodic menstrual bleedings appeared at puberty. The endocrinologic data demonstrated the secretory activity of both the ovarian and the testicular tissue. The analysis of red cell, lymphocyte and serum markers, done on the propositus and on his parents, failed to show any evidence of double fertilization. On this basis, the origin of the XX/XY condition (mosaicism versus chimerism) and its developmental consequences are discussed.

Serologic detection of a y-linked gene in xx males and xx true hermaphrodites

To test the hypothesis that H-Y antigen (present on both somatic and germ cells in normal males but not normal females) is essential for testicular differentiation, we studied four XX males and three XX true hermaphrodites. Blood cells from six subjects and cultured gonadal fibroblasts from a seventh expressed H-Y antigen. Since expression of this antigen requires the presence of a gene normally carried by the Y chromosome, this gene, and perhaps additional Y chromosomal material, should have been present in the genome of these subjects. In one patient this presence is accounted for by a Y-to-X translocation, detectable by chromosome banding. In another a normal Y chromosome was present in a minor population of cells. In the remaining five, no karyotypic abnormality was detectable. Immunologic detection of H-Y antigen is a sensitive test for the presence of the Y chromosome or of its male-determining segment.