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The chromosome caper

illustration for TH Open

illustration for TH Open  

The ‘Y’ type is found in the organs of women who had borne a male foetus, long after pregnancy

The human foetus is the most demanding compared with those of other mammals. As a consequence, it has the most complex and invasive placenta, burrowing deep into the wall of the uterus asking for more. The mother has no choice but to oblige.

In a hospital outpatient department in Kerala, as patients’ names are called, I have noted a common suffix to the names of many women. Most of those above 60 years of age have it: Amma, meaning mother. Devakiamma, Kamalamma, Radhamma; their maiden name, I am sure, did not carry that suffix. At some point of their life, Devaki, Kamala and Radha transformed to Ammas. You have guessed it right, it happened after childbirth.

Childbirth brings about a lot of anatomical, physiological and psychological changes to a woman; almost all physiological changes normalise, many anatomical changes revert, but psychological changes don’t. The name too sticks.

Long travel

In a study published in the Journal of Molecular Human Reproduction recently, researchers looked for the presence of the Y chromosome (the ‘male’ chromosome) by a sensitive technique called in situ hybridisation in women who died with a male foetus during late pregnancy or immediately after delivery. They found that the Y chromosome in the foetus had travelled to the mother, not just in the blood but also into most major organs such as brain, lungs, kidneys, liver and spleen. They were present in 100% autopsy samples from the brain, spleen and lungs, 95% from the liver and 29% from the heart.

A chimera

Another ground-breaking finding in 2012 was detection by autopsy of the Y chromosome in the brain of 63% of the mothers long after delivery. The oldest woman studied was 94 years old. The Y chromosome had no business to be there, except that all these women had mothered at least one male child.

A normal human being carries a single line of DNA. Rarely do people carry two lines, called “chimerism”, named after the part-lion, part-goat fire-breathing mythological monster.

Scientists have created “chimeric” lab animals, but “chimerism” is known to occur in humans either by birth (dizygotic twins, one of which gets merged to the other) or after organ transplant (bone marrow transplant).

The long-term effects of such a rare phenomenon are unknown.

While true “chimerism” is rare, “micro-chimerism”, seen after pregnancy and delivery, is probably not that uncommon. All that we can say is that the apparently helpless foetus, nurtured deep down in the mother’s womb, tends to hijack the maternal system in ways which is much beyond our understanding.

There are scientists who believe that “micro-chimerism” leads to changes in the hormonal status of women after pregnancy, and perhaps protects the mother from diseases such as cancer and heart disease, improving maternal survival for the baby’s benefit — not just in the short term but in the years to come.

I always thought, but never had the courage to profess, that my wife loves and cares for our children more than I do. Now I think I know why.

tinynair@gmail.com

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Printable version | Apr 1, 2020 11:16:09 AM | https://www.thehindu.com/opinion/open-page/the-chromosome-caper/article30712610.ece

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