46,XY/46,XY Chimerism: Prenatal Presentation and Postnatal Outcome

Human chimerism is rare, and most prevalent with discordant chromosomal sex. We report a male 46,XY/46,XY chimera, born through a spontaneously conceived pregnancy to a healthy 32-year-old G1P0 Indian, African, and Scottish female and her 34-year-old healthy Chinese partner. The prenatal presentation and postnatal outcomes are described.

A prenatal cell-free DNA screening test, amniocentesis with QF-PCR and SNP microarray, and postnatal microarray and FISH study on peripheral blood, placenta, and umbilical cord were used to evaluate chimerism.

The prenatal cell-free screening test revealed high risk for triploidy/vanishing twin, but there was no confirmation from early ultrasound. Subsequent QF-PCR on amniocytes showed a profile suggestive of a tetragametic chimera. G-banding showed a 46,XY karyotype. A SNP microarray detected two copy number gains of uncertain significance on chromosome 6q, derived from the father who was a balanced carrier of ins(6;11). A postnatal microarray and FISH study confirmed the presence of two cell lines, each with a 46,XY complement but with different submicroscopic structural changes including recombinant and insertion changes. Clinical evaluations of the child at birth and 8 weeks of age were coordinated to detect the presence of chimeric symptoms.

With a confirmed incidental finding of 46,XY/46,XY chimerism, we present that underlying same-sex chimerism may be under-recognized.