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

Area of Science:

• Human Genetics
• Reproductive Biology
• Medical Diagnostics

Background:

• Human chimerism, the presence of two distinct cell lines in one individual, is a rare phenomenon.
• Chimerism is most commonly observed when there is a discordant chromosomal sex between the cell lines.
• This report details a unique case of same-sex chimerism in a male individual.

Purpose of the Study:

• To document and describe a rare case of male 46,XY/46,XY chimerism.
• To outline the diagnostic process, from prenatal screening to postnatal confirmation.
• To highlight the potential for under-recognition of same-sex chimerism.

Main Methods:

• Prenatal diagnosis utilized cell-free DNA screening, amniocentesis with quantitative fluorescent polymerase chain reaction (QF-PCR), and single nucleotide polymorphism (SNP) microarray.
• Postnatal evaluation included microarray and fluorescence in situ hybridization (FISH) studies on peripheral blood, placenta, and umbilical cord.
• Clinical assessments at birth and 8 weeks monitored for chimeric symptoms.

Main Results:

• Prenatal screening initially suggested triploidy or a vanishing twin, but this was not ultrasonographically confirmed.
• QF-PCR indicated tetragametic chimerism, and G-banding showed a 46,XY karyotype.
• Postnatal analyses confirmed two 46,XY cell lines with distinct submicroscopic structural variations, including recombinant and insertion changes, with one copy number gain on chromosome 6q linked to the father's balanced carrier status.

Conclusions:

• The case confirms a diagnosis of 46,XY/46,XY chimerism.
• The findings suggest that same-sex chimerism is an under-recognized condition in human genetics.
• This case underscores the importance of advanced genetic testing in diagnosing rare conditions.