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      The identification of a spontaneous 47, XX, +21/46, XY chimeric fetus with male genitalia

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          Approximately 30 sex-chromosome discordant chimera cases have been reported to date, of which only four cases carried trisomy 21. Here, we present an additional case, an aborted fetus with a karyotype of 47,XX, +21/46,XY.

          Case presentation

          Autopsy demonstrated that this fetus was normally developed and had male genitalia. Major characteristics of Down syndrome were not observed except an enlarged gap between the first and second toes. Karyotyping of tissues cultured from the fetus revealed the same chimeric chromosomal composition detected in the amniotic fluid but with a different ratio of [47,XX,+21] to [46,XY]. Further short tandem repeat analysis indicated a double paternal contribution and single maternal contribution to the fetus, with the additional chromosome 21 in the [47,XX,+21] cell lineage originating from the paternal side.


          We thus propose that this chimeric fetus was formed via the dispermic fertilization of a parthenogenetic ovum with one (Y) sperm and one (X,+21) sperm.

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          Most cited references 10

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          A true hermaphrodite chimera resulting from embryo amalgamation after in vitro fertilization.

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            Chimera and other fertilization errors.

            The finding of a mixture of 46,XX and 46,XY cells in an individual has been rarely reported in literature. It usually results in individuals with ambiguous genitalia. Approximately 10% of true human hermaphrodites show this type of karyotype. However, the underlying mechanisms are poorly understood. It may be the result of mosaicism or chimerism. By definition, a chimera is produced by the fusion of two different zygotes in a single embryo, while a mosaic contains genetically different cells issued from a single zygote. Several mechanisms are involved in the production of chimera. Stricto sensu, chimerism occurs from the post-zygotic fusion of two distinct embryos leading to a tetragametic chimera. In addition, there are other entities, which are also referred to as chimera: parthenogenetic chimera and chimera resulting from fertilization of the second polar body. Furthermore, a particular type of chimera called 'androgenetic chimera' recently described in fetuses with placental mesenchymal dysplasia and in rare patients with Beckwith-Wiedemann syndrome is discussed. Strategies to study mechanisms leading to the production of chimera and mosaics are also proposed.
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              Prenatal diagnosis and normal outcome of a 46,XX/46,XY chimera: a case report.

              The phenotypic spectrum of 46,XX/46,XY chimeric patients is variable. It ranges from normal male or female genitalia to different degrees of ambiguous genitalia. Chimerism results from the amalgamation of two different zygotes in a single embryo, whereas mosaicism results from a mitotic error in a single zygote. Several other mechanisms resulting in a chimera have been discussed in the literature. Here, we report on a new case of chimerism (46,XX/46,XY) diagnosed at 17 weeks' gestation on amniocentesis performed because of advanced maternal age. Ultrasound examination revealed normal female external genitalia, and a healthy baby girl was delivered at term. We used polymorphic markers spanning the X chromosome and several autosomes in order to identify the genetic mechanism involved. Mosaicism was excluded because of the presence of 3 alleles at 11 autosomal and 4 X chromosome loci. On autosomes, the origin of this third allele was maternal for two pericentromeric markers (located on 2p11.2 band and 8p11.2 band), paternal for six markers and paternal or maternal for the other three markers. On the X chromosome, the origin of the third allele was maternal for all four markers. Thus, two different paternal and maternal haploid sets were observed. These results are compatible with a tetragametic chimera.

                Author and article information

                BMC Med Genet
                BMC Med. Genet
                BMC Medical Genetics
                BioMed Central
                20 September 2012
                : 13
                : 85
                [1 ]Laboratory for Cytogenetics, Center for Genetic Counseling, Buddhist Tzu Chi General Hospital, 707, Sec 3, Chunyang Rd, Hualien, 970, Taiwan
                [2 ]Graduate Institute of Medical Sciences, Tzu Chi University, Hualien County, 970, Taiwan
                [3 ]Department of Obstetrics & Gynecology, Buddhist Tzu Chi General Hospital, Dalin Branch, Chiayi County, 622, Taiwan
                [4 ]Department of Medical Laboratory Science and Biotechnology, National Cheng Kung University, 1, University Road, Tainan City, 701, Taiwan
                [5 ]Department of Urology, Buddhist Tzu Chi General Hospital, 707, Sec 3, Chunyang Rd, Hualien County, 970, Taiwan
                [6 ]Department of Molecular Biology and Human Genetics, Tzu Chi University, 701, Sec 3, Chunyang Rd, Hualien, 970, Taiwan
                Copyright ©2012 Lee et al.; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Case Report


                karyotype, sex chromosome, fetus, trisomy 21, genitalia, chimerism


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