46,XX/46,XY Chimerism & Human Sexual Development

The term chimera refers to an organism with cell lines from two or more distinct zygotes. Human chimerism may occur naturally or artificially. Although rare, advancements in genetics and genomics have resulted in the identification of additional natural human chimeras. Three forms of naturally occurring chimerism have been documented in humans: blood group chimerism, microchimerism, and fusion chimerism. Fusion chimerism may occur through several means. Sex-chromosome discordant chimerism refers to individuals with both XX and XY cell lines. There is a large amount of phenotypic variability among 46,XX/46,XY chimeric individuals. The care of people with intersex traits or DSD (Disorders of Sexual Development) is controversial due in part to a history of unnecessary surgical intervention and power-imbalances between the intersex and medical communities. As more 46,XX/46,XY chimeric individuals with intersex traits or DSD are identified, the implications for their care will need to be clarified.