Three Parent Babies: Everything explained

The 'Three Parent Baby' mechanism involves the replacement of a small amount of faulty DNA in a mother’s egg with healthy DNA from a second woman. This results in the baby inheriting genes from two mothers and one father. The idea is to prohibit certain genetic diseases being passed on to children.

Created On: Jan 4, 2017 12:49 IST

In simple words when a baby is born from the DNAs of three people then we generally call it a three- parent- baby. But in order to know its exact meaning, we will have to discuss its technical terms also. The first three- parent baby was born recently in the USA with the help of a technique. The technique replaces a small amount of faulty DNA in a mother’s egg with healthy DNA from a second woman. This results in the baby inheriting genes from two mothers and one father.

Mechanism of 3 parent BabyThe idea is to prohibit certain genetic diseases being passed on to children. The technique which was used in achieving this landmark in the history of medical science is known as Spindle transfer. This technique is explained in detail below.

The first baby, with the help of Swindle transfer, was born on 6 April after his Jordanian parents traveled to Mexico where they were cared for by US fertility specialists. The first baby’s mother has genes responsible for the fatal Leigh syndrome. Leigh syndrome is a neurological disorder which harms the developing nervous system. The faults directly affect the DNA in mitochondria, the small battery-like structures that provide cells with energy, and are passed down from mother to child.

The wife became pregnant after the then years of marriage but she lost the baby in the first of four miscarriages. The mother gave birth to a baby girl in 2005 who died at the age of six, and later, a second child who lived for only eight months. Medical Tests on the wife revealed that while she was healthy, about one-quarter of her mitochondria carried the genes for Leigh syndrome. The couple lost two children to the disease before asking for the clinic’s help.

The couple approached Zhang, from the New Hope Fertility Center in New York, for help and guidance, he decided to try the mitochondrial transfer procedure. He took the nucleus from one of the woman’s eggs and inserted it into a healthy donor’s egg that had had its own nucleus removed. He then fertilized the egg with the husband’s sperm. The US team created five embryos but only one developed normally. This was implanted into the mother and the baby was born nine months later.

The baby is not the first child to be born with DNA from three people. Fertility doctors tried to improve the quality of women’s eggs by injecting cytoplasm. Cytoplasm is the cellular material that contains mitochondria, from healthy donor eggs. This technique led to several babies being born with DNA from the parents and the healthy donor.  But some of the children who were born, developed genetic disorders and the procedure was banned. However, this technique offered hope to mothers who carried mitochondrial DNA mutations.

The first legislation of Three- Parent Baby:

Mitochondrial transfer was first legalized in the UK in 2015 but so far no other country has introduced laws to permit the technique. U.K. fertility clinic regulator Human Fertilization and Embryology Authority (HFEA) has agreed to permit the “cautious use” of the technique, developed by British scientists. This technique replaces an egg’s defective mitochondrial DNA with healthy mitochondrial DNA from another female donor to prohibit the child from suffering from genetic flaws. The aim of this technique is meant for those parents who have a high risk of passing on debilitating and even fatal genetic diseases to their children.

Despite serious ethical and medical concerns, the U.K became the first country to legalize three-parent babies after its fertility regulator, Human Fertilization and Embryology Authority (HFEA) had approved the process. This decision was taken 2 weeks after an independent expert scientific panel assembled by HFEA published its fourth review of the safety and efficacy of mitochondrial donation.

The panel also opined that the technique could be used prudently for risk reduction treatments in certain cases where alternative treatments would be of little or no benefit to mothers at risk of passing mitochondrial disease on to their children.

Mitochondrial Problem:

As we know that, Mitochondria are a double-membraned cellular organelle, which is responsible for generating energy. Mitochondria are commonly known as the powerhouse of the cell, but what really makes them unique is that they are divided independently of the cell. They consist of a very small genome of their own, which in many ways duplicate that of more primitive life forms. The mitochondrial DNA controls its functions much like the rest of any living form and decides how the organism would look and act like.

Mitochondria hold almost 0.0005% of our entire DNA, but the child receives it only from the mother. This makes any aberrations in mother’s mitochondrial DNA that may cause diseases is passed on completely to the child. The New York Stem Cell Foundation Research Institute revealed a data which says approximately 1 in 5,000-10,000 children is born each year with mitochondrial disease. These diseases can be devastating diseases.

The symptoms of these diseases are often aroused in childhood. Symptoms can include neurological disorders, stunted development, stomach and digestive problems, heart disorders among others, and can result in childhood death. There are no cures for these diseases but only symptom management is possible.
How these figures are applicable for India it is not sure yet.

Some studies show that some diseases where aberrations in the mitochondrial DNA might have a role to play in Parkinson’s, Alzheimer’s, and Type II diabetes.

Technique for Treatment: Spindle transfer

We now know that the boy’s mother carries a rare disease called Leigh syndrome and the couple also lost two children to the disease before asking for the clinic’s help. The clinic’s team replaced the nucleus of the mother’s egg cell to the egg of a donor with healthy mitochondria and its nucleus removed. It was done in an attempt to create embryos without the mother’s faulty mitochondria. This technique is known as spindle transfer. Then the egg was fertilized by the father’s sperm.

Zhang’s team created five embryos by above mentioned way and one of which was implanted into the mother and survived to birth. The baby inherited nuclear DNA from both parents and mitochondrial DNA from the donor. If verified, the achievement of Zhang team’s would represent the first child born with the help spindle transfer technique mitochondrial-replacement therapy (MRT).

In the United States, MRT is in principle allowed but requires review and approval by the US Food and Drug Administration (FDA). Women with faulty mitochondrial DNA who want to have children can opt for IVF using eggs from a healthy donor. But two experimental techniques could allow affected women to have healthy babies that are genetically related to them. 

The Zhang’s procedure was performed in Mexico. Zhang told the reason that there are flexible rules in Mexico about gene transplantation. In the U.S. there are laws governing the manipulation of human genes but they are vague and unclear. So Zhang preferred to go to Mexico for performing this task.

Ethical Issues

This issue has triggered debate amongst scientist, researchers and other intelligentsia that how and when this method should be used. And it also raised some questions about the ethical justifications of this method. And there are other concerns too which involve uncertainty in the success of such methods.

Embryologist Jacques Cohen, who carried out mitochondrial-transfer procedures in the 1990s and who was also a regulatory adviser on Zhang’s study, and welcomes the news that the spindle-transfer method seems to be effective.  He said “the world is ready to try this out. It has been discussed for a long time. He adds there are risks, but that’s what happens when you do an experimental procedure for the first time.” Cohen’s clinic produced 17 babies before the US began to regulate MRT in 2002.

But some other researchers are concerned and troubled by Zhang’s announcement.  They say “Zhang’s team just went ahead and did it. And they did not consider the number of issues that are still unresolved .it’s just staggering.”

There are concerns about the possibility that the technique could also transfer some diseased mitochondria from the mother into the donor egg along with the nucleus. Zhang’s abstract claims only 5% of the embryo’s mitochondrial DNA that carried over along with the nucleus was the mother's, but mitochondrial DNA samples taken from the baby after birth varied from tissue to tissue and suggested a level of faulty DNA that was, on average, 1.6%. 

At the end, it is reasonable to go with the scientific spirit and get less hampered by other doubts before seeing the complete outcome of the treatment.

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