Semi-identical’ twins discovered

Researchers have discovered a pair of twins who are identical through their mother’s side, but share only half their genes on their father’s, reports a News Exclusive from news@nature.com.
The ‘semi-identical’ twins are the result of two sperm cells fusing with a single egg, before becoming two embryos — a previously unknown way for twins to come about, say the team that made the finding. The twins are also chimaeras, meaning that their cells are not genetically uniform. Each sperm has contributed genes to each child.
The twins’ genetic makeup was investigated because one was born with ambiguous genitalia. One turned out to be a ‘true hermaphrodite’, with both ovarian and testicular tissue. The other twin is anatomically male.
Such twins are probably very rare. Their existence and discovery relies on three unusual, and possibly unlinked, events: first, that an egg fertilized by two sperm develops into a viable embryo; second, that this embryo splits to form twins; and third, that the children come to the attention of science.
This was reported in the Journal of Human Genetics, the news of this report comes exclusively from news@nature.com.
CONTACTS
Mikhail Golubovsky (Duke University, Durham, NC, USA)
mgolub@cds.duke.edu
Vivienne Souter (Banner Good Samaritan Medical Center in Phoenix, AZ, USA)
vsouter@yahoo.com
David Bonthron (University of Leeds, UK)
d.t.bonthron@leeds.ac.uk
Contact for background information only:
John Whitfield (Journalist, news@nature.com)
Tel: +44 20 7843 4645;