For the first time in the history of medicine, doctors have discovered a very rare form of human twins during pregnancy. They are neither monozygous nor heterozygous. Only one pair of twins of this species is known throughout the world. What makes these twins so special is explained by the medical team that looked after their mother and twins.
What are these special twins?
Semi-identical twins arise when 2 sperm fertilize an egg at the same time. Usually the egg ceases to develop further in this case. But in this extremely rare case, the semi-identical twins survived and now they are 4 years old. A medical sensation has recently been described in the British Medical Journal.
The case from Australia attracted the attention of the whole world.
For the first time, doctors were able to track how 2 embryos of 3 genes develop. At normal birth, the embryo divides the genetic material of the mother and father into equal parts.
In monozygotic twins, the embryo is divided into 2 completely identical parts after fertilization. When dizygotic twins developed, the mother had two eggs that were fertilized by different sperm.
Twins of three genes
Homozygous and heterozygous twins survive relatively often. However, if two sperm fertilize the egg at the same time, this becomes a special case. Now it is twice the genetic material of the father and once the genetic material of the mother.
Three sets of chromosomes are usually incompatible with life, and embryos usually do not survive. As a clinical geneticist and coordinator of diagnostic genomics at the Institute of Health and Biomedical Innovation, a specialist investigated this case.
Ultrasound of the mother showed one placenta after 6 weeks. At first, the doctors suspected that they were identical twins. However, at 14 weeks of gestation, it turned out that one of the twins was a woman and the other a man. The twins survived and are absolutely healthy. Doctors could not detect any developmental anomalies.
The same genetic material of the mother is different from the father
The DNA of the twins has already been examined in the womb. Doctors found that embryos share 100% of the mother’s genetic material. However, on the part of the father, the brothers and sisters received various genetic information. Thus, semi-identical twins form the third and extremely rare type of twins.
This type of twins was first discovered in the United States in 2007. There were many of them in infancy, because one of the twins did not have a unique gender.
After a genetic examination, it was also revealed that the twins' DNA was identical on the maternal side, but they only have half of the paternal DNA.
Only 2 semi-identical twin pairs are known worldwide
When this case became known for the second time, the medical team wondered if there were such semi-identical twins. They examined the genetic database of 968 twins and their parents, but could not find another case.
Thus, semi-identical twins and those from the USA are the only known pairs of twins of this species throughout the world.
Perhaps, according to scientists, there are officially unrecorded cases of the birth of semi-identical twins.
What happened in the USA?
When the woman was 10 weeks pregnant, the doctor told her that she and her husband would have twins. But soon the doctor discovered 2 palpitations. The surprise was huge when they said that there would be four children and two pairs of twins.
According to a pregnant woman, she did not take any hormonal drugs. The couple planned a pregnancy, but became overly "successful." However, a large number of children did not upset them at all.
They said that "they are glad for the appearance of several children, and each will be taken care of equally."
The probability of obtaining semi-identical twins in a natural way with one pregnancy is estimated by experts as 1 out of 4 billion.
The probability of winning the lottery is just over 1 in 14 million. The case is extremely rare and, according to experts, it is not known whether the children will survive in the future. Additional examinations are currently underway.
