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.
Malan
V
V
Service de Cytogénétique, Hôpital Necker - Enfants Malades, APHP, Paris, René Descartes-Paris 5 University, Paris, France. valerie.malan@nck.aphp.fr
Vekemans
M
M
Turleau
C
C
D002678:Chimera / Q000235:genetics*; D005260:Female; D005306:Fertilization / Q000235:genetics*; D006801:Humans; D008297:Male; D008957:Models, Genetic; D009030:Mosaicism; D050090:Ovotesticular Disorders of Sex Development / Q000235:genetics; D010312:Parthenogenesis / Q000235:genetics; D011123:Polyploidy; D011247:Pregnancy; D024182:Uniparental Disomy