Aussie doctors discover 'exceptionally rare' semi-identical boy and girl twins

The sesquizygotic twins share 100% of their mother's genes but only a proportion of their father's DNA

A set of Australian twins — a boy and a girl — have been identified as just the second in the world to be created from one egg and two sperm, and the first to be discovered during pregnancy.

Semi-identical twins are extraordinarily rare, according to New England Journal of Medicine report on the twins born in Queensland four years ago.

They are the first case to be seen in Australia; however, it has taken researchers several years to confirm they are in fact sesquizygotic.

The twins share 100% of their mother's genes but only a proportion of their father's DNA.

“We know this is an exceptional case of intermediate twins, also known as a third type of twinning,” says co-author Professor Nicholas Fisk, a fetal medicine specialist who led the team that cared for the mother and twins at the Royal Brisbane and Women’s Hospital in 2014.

“While doctors may keep in