Placenta resembles a tumour and is dumping ground for genetic defects, say scientists

Study finds ‘clear parallel’ with development of cancer

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The structure of the placenta resembles that of a tumour, and harbours many of the same genetic mutations found in childhood cancers, new research suggests.

In the first study of the genomic architecture of the human placenta, scientists have found its make-up is different from that of any other human organ, and say the findings support the theory of the placenta as a dumping ground for genetic defects, whereas the foetus corrects or avoids them.

In early pregnancy, the fertilised egg begins dividing into cells, some of which will form the placenta.

In one to two per cent of pregnancies, some placental cells have a different number of chromosomes from cells in the foetus - a genetic flaw that could be fatal to the foetus, but with which the placenta often functions reasonably normally.

But problems with the placenta are a major cause of harm to the mother and unborn child.

Steve Charnock-Jones, a senior author of the study from the University of Cambridge, said: “The rates and patterns of genetic mutations were incredibly high compared to other healthy human tissues.”

Scientists at the Wellcome Sanger Institute and the University of Cambridge conducted whole genome sequencing of 86 biopsies and 106 microdissections from 42 placentas. They found each biopsy was a genetically distinct “clonal expansion” - a cell population descended from a single common ancestor.

This indicated a clear parallel between the formation of the human placenta and the development of a cancer, according to the study, published in Nature.

Analysis also identified patterns of mutation found in childhood cancers, such as neuroblastoma, with an even higher number in the placenta than in the cancers themselves.

Sam Behjati, a senior author of the study from the Wellcome Sanger Institute, said: “The placenta is akin to the ‘wild west’ of the human genome, completely different in its structure from any other healthy human tissue. It helps protect us from flaws in our genetic code, but equally there remains a high burden of disease associated with the placenta.”