When an egg and sperm fuse in human pregnancy, the developing ball of cells has the potential to differentiate into just about anything in the human body. Some will form the placenta, a unique organ that essentially hacks the mother’s circulatory system as a means of perfusing the developing fetus (sometimes collecting soot and microplastics in the process). It can even moderate the blood, removing waste products and regulating hormones to the benefit of mother and baby. Now, new research published in the journal Nature has found that the talents of the placenta don’t stop there, as researchers discovered evidence supporting the theory that the placenta is like a "dumping ground" for genetic defects.
The study is the first of its kind in carrying out such an in-depth analysis of the architecture of the human placenta, revealing its anatomy is less like that of a human organ and more like that of a tumor. Carried out at the Wellcome Sanger Institute and the University of Cambridge, UK, the study concluded that healthy placentas harbor lots of genetic mutations – some of which have been linked to childhood cancers.
The placenta was already understood to be an unusual organ as in around one to two percent of pregnancies, the cells within the placenta can have a chromosome count that differs from the fetus. Were this genetic abnormality to be present in the fetus instead of the organ it’s connected to, it would likely be fatal – and yet the placenta is able to carry on ticking off most of its chores without much difficulty.
The findings were revealed after the team sequenced the genomes of multiple samples taken from 42 placentas, extracting the biopsies from different areas to get an idea of its genetic makeup as a whole organ. It revealed that each biopsy was genetically distinct from other biopsies taken from the same organ despite sharing a common ancestor, drawing parallels with the formation of a cancerous tumor.
“Our study confirms for the first time that the placenta is organised differently to every other human organ, and in fact resembles a patchwork of tumours,” said Professor Steve Charnock-Jones, a senior author of the study from the University of Cambridge, in a statement. “The rates and patterns of genetic mutations were also incredibly high compared to other healthy human tissues.”
The study supports the idea that the placenta may be used as a dumping ground for cell lineages with harmful mutations, allowing developing fetuses to effectively iron out flaws in their genetic makeup. A worthy cause, but this tumor-like organ isn’t without its flaws.
“The placenta is akin to the ‘wild west’ of the human genome, completely different in its structure from any other healthy human tissue,” said Dr Sam Behjati, a senior author of the study from the Wellcome Sanger Institute in a statement. “It helps to protect us from flaws in our genetic code, but equally there remains a high burden of disease associated with the placenta. Our findings provide a rationale for studying the association between genetic aberrations in the placenta and birth outcomes.”