Tumours passed between two identical twins before birth, both died shortly after birth

What a tragic story!

"A genetic analysis has revealed a rare case of a tumour passing from one identical twin to another in utero. The twins died shortly after birth and the

family gave consent for researchers to study their cancers.

The team found that the mutations in the tumour cells taken from each twin were too genetically similar for them to have arisen independently, meaning that the cancer must have passed from one twin to the other."

From the abstract:

"Studying monozygotic twins who present with identical cancers informs on the developmental origins of childhood tumours.

Here, we perform whole genome sequencing on multiple tumour, normal, and placental samples to reconstruct the phylogeny of a soft tissue cancer that spread in utero between monozygotic twins.

We demonstrate the origin of the tumour from one twin and time its diversification and transplacental spread to the other twin, showing that the spread occurred only once.

This generalisable and scalable approach additionally allows us to dissect the earliest stages of twinning, revealing unexpected asymmetrical contributions of embryonic lineages to the placenta and each twin and challenging the classical model of twinning."

Nature Briefing: Cancer

Scientists Trace How Cancer Passed Between Twins Before Birth

Embryonic origin of cancer in newborn twins (open access)

Genetic differences between monozygotic twins

Amazing stuff coming again out of tiny Iceland!

"Despite the important role that monozygotic twins have played in genetics research, little is known about their genomic differences. Here we show that monozygotic twins differ on average by 5.2 early developmental mutations and that approximately 15% of monozygotic twins have a substantial number of these early developmental mutations specific to one of them. ..."

"... Rather than having exactly the same DNA sequences, twins start accumulating genetic variation from the earliest stages of development, researchers at Iceland-based company deCODE genetics [founded in 1996] found, meaning that one twin harbors variants that aren’t present in the other. ...

The new study focuses specifically on mutations that occur as or before embryos form from the mass of cells inside the blastocyst, a structure that implants in the uterine wall. During this stage of development, this inner cell mass can split to form two separately developing embryos.

Drawing on deCODE’s genetic databases to analyze variation in multiple cells sampled from 381 monozygotic twin pairs and their immediate family members, the researchers pinpointed a number of mutations that arose during this stage of development in just one member of each pair, meaning that at birth, so-called identical twins may already differ genetically from each other.

"

Differences between germline genomes of monozygotic twins | Nature Genetics

Identical Twins Accumulate Genetic Differences in the Womb (contains interview with CEO of deCode genetics)

Kári Stefánsson, CEO