Chromosome quirks: a girl with the XY karyotype
The boy mutated into a girl asexuallyPyotr Smirnov, "Newspaper.
Ru»The birth of a healthy girl with a Y chromosome showed that it was not enough for a boy to develop from an embryo with an indeterminate sex.
A mutation on the incomplete 17th chromosome can turn a "genetic boy" into a girl.
Modern perinatologists have at their disposal such a large number of various fetal examination tools that parents now rarely have to think about two lists of names at once, male and female. And if the interpretation of ultrasound is very rare, but it may still turn out to be erroneous, then karyotyping of the fetus – determining a set of chromosomes – never fails with careful execution.
It is for this reason that Swiss doctors were very surprised when a completely healthy girl was born seven years ago during childbirth.
Fetal karyotyping is not a mandatory procedure, but since the expectant mother was already aged, the doctors recommended to conduct this procedure to exclude congenital chromosomal abnormalities. They are responsible for up to 50% of spontaneous abortions and about 7% of all stillbirths. And the frequency of Down syndrome caused by the tripling of the 21st chromosome makes parents seriously think about early diagnosis.
Conducted at the stage of embryonic development and repeated karyotypic analysis, for obvious reasons, carried out after childbirth, did not reveal any abnormalities in the structure of any of the 46 chromosomes, the list of which ended with an XY pair. But there was clearly a girl in front of the doctors.
In clinical practice, this is by no means the first case, and such situations should fall under the definition of Shereshevsky-Turner syndrome. It can develop with karyotype 45X0, when there is only one of the two sex chromosomes – female, or, in the case of chimerism, 46Xq – when there are cells in the body with a different set of chromosomes.
In this case, doctors at birth conduct a thorough examination to remove the underdeveloped sex glands, prone to the formation of tumors. During the operation, the surprise only became greater – the surgeons did not find any traces of underdeveloped, or rather, undecided in the direction of their development of gonads, shrunken testicles or other congenital anomalies. Instead, the authors of the publication in the American Journal of Human Genetics saw a "chromosomal boy" with a full-fledged vagina, cervix and normal, healthy ovaries.
They took a small pinch of the latter for genetic and cytological analysis. The first assumption – that the fault was a defect in the SRY region, located on the "male" Y chromosome and playing a key role in determining gender, could not be proved.
But the authors found a defect on the 17th chromosome in the CBX2 gene, which has already been noticed once in a similar effect in laboratory mice.
Anna Biason-Lauber from the University Children's Hospital, who led the work, believes that CBX2 helps the SRY gene to realize its function. That is why, even if there is a full-fledged SRY on a full-fledged Y chromosome, the female sex of the child does not cause doubts.
In the absolute majority of cases, SRY triggers the work of two proteins at the stage of embryonic development. One of them promotes the conversion of testosterone into estradiol, which stimulates the development of male sex glands. The second SRY-encoded factor prevents the development of the Muller ducts – the future fallopian tubes characteristic of the female body.
Now scientists face another question – will the girl be able to have children? Laboratory mice with a similar defect on chromosome 17 are sterile. However, in the case of a 7-year-old child who has fallen under the care of a research team, everything is not so obvious. After all, the ovaries responsible for the storage and formation of germ cells, and all the necessary genitals are present and quite healthy.
Portal "Eternal youth" www.vechnayamolodost.ru13.04.2009