A study published March 10 in the journal Nature found that the human placenta is closer in structure to a tumor than to a human organ, and that it retains a large number of defective genes in order to reduce fetal acquisition of defective genes, acting as a “dumping ground” for defective genes.
The researchers say this is the first study to date to analyze the genes and structure of the human placenta in such depth. The study, done jointly by the University of Cambridge and the Wellcome Sanger Institute, said that even a perfectly healthy placenta carries many mutated genes, some of which are associated with childhood cancer.
Prior to this study, it was recognized that the placenta was not an ordinary human organ and that in about 1 to 2 percent of pregnancies, the number of chromosomes in the placental cells did not match that of the fetus. If this abnormality occurred in the fetus and not in the placenta, it would be a fatal defect. However, even so, these placentas were able to perform all the tasks of fetal gestation normally.
The researchers genetically sequenced 42 placentas and examined biopsy samples from different locations on each placenta. It turned out that the genetic makeup of cells at different locations on the same placenta was not the same. This is the same characteristic of tumors.
“Our study confirms for the first Time that the placenta is not structured like any organ in the body, and that it is actually more like a patchwork of various tumors put together.” One of the lead authors of this study, Cambridge University professor Charnock-Jones (Steve Charnock-Jones), said, “The proportion of mutated genes inside the placenta is also much higher than in healthy human organ tissue.”
A previous theory suggested that one use of the placenta might be as a “dumping ground” for mutated cells, allowing the growing fetus to keep defective genes in the placenta and grow up healthy. This role of the placenta is so altruistic that it makes the placenta a defective human organism in its own right. The researchers say the findings of this study provide evidence for this theory.
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