Triple X syndrome is a common variant of aneuploidy in women, in which an additional female sex chromosome is present in the karyotype. The condition may be manifested by the early onset of menarche, delayed neuropsychiatric development, emotional lability. At the same time, in most women, the syndrome is asymptomatic, often the pathology is not diagnosed at all. The examination includes karyotyping, examination by a neurologist. Treatment is not required, regular extended follow-up is indicated for the prevention and correction of complications.
This variant of chromosomal abnormality occurs quite often — on average in 1 out of 1000 women. A genetic disorder is diagnosed in about 10% of cases, since most patients do not have any abnormalities in their health, do not seek medical help. However, sometimes with triple X syndrome, neurological disorders, problems with the reproductive system are observed, which causes a great urgency of the problem in modern genetics, the need to identify women from risk groups and their medical examination.
The development of trisomy syndrome is associated with the non-divergence of the X chromosome at the stage of germ cell formation. More often, girls receive an additional chromatid from their mother if an egg containing 2 female sex chromosomes is used during fertilization. When the genetic materials of the mother and father merge at the moment of conception, a zygote is formed, which has 3 X chromosomes and subsequently gives rise to all the cells of the unborn child’s body. The predisposing factors of the anomaly have not yet been established.
In most cases, there is a complete form of trisomy with the presence of an additional chromosome in all cells of the woman’s body. Less common are mosaic variants when there are 2 types of cells in the body at the same time — normal with a diploid set of chromosomes 46, XX and aneuploid with the formula 47, XXX. Signs of trisomy are also present in the mosaic form of Shereshevsky-Turner syndrome, when cells with 45, X and 47, XXX are present.
The presence of one additional X chromosome in the karyotype is usually not particularly dangerous, which is explained by the peculiarities of the functioning of the genetic material in women. Normally, with a set of 46, XX, one of the sex chromosomes has a heterochromatin structure, forms a Barr body and is inactive. With trisomy, 2 Barr bodies are formed on the female sex chromosome, which do not participate in the functioning of the cell, practically do not affect molecular processes.
Girls with the genetic triple X syndrome are born full-term with an average weight of about 3000 g, reduced head circumference. Occasionally, newborns have a decrease in muscle tone, a slight delay in the formation of psychomotor functions. At the age of 1-5 years, hypermobility of the joints, muscle hypotension, which interferes with the normal formation of large and small motor skills, can disturb.
Occasionally there are psychological disorders in the form of mood swings, outbursts of anger, emotional lability. Clinically pronounced trisomy of the X chromosome is also characterized by earlier periods of puberty, premature onset of menstruation. These changes do not affect the fertility of women, the risk of infertility and pregnancy pathologies in them corresponds to that in the population.
The most dangerous consequence of triple X syndrome is mental retardation. Some girls with such a genetic anomaly later begin to speak, have difficulty reading, lag behind their peers in terms of knowledge in school subjects. Also, patients may have problems communicating with peers, poor communication skills, but often these problems disappear as they grow up.
Of great importance in the occurrence of complications is the timeliness of diagnosis and rehabilitation measures. According to the WHO, of the girls whose chromosomal abnormality was diagnosed shortly after birth, only 14% faced problems with learning, whereas with a later diagnosis, the proportion of such children is 30-50%. On average, about 25-30% of girls at the end of school have grades below the average.
During a standard pediatric or therapeutic examination, no specific signs of triple X syndrome are determined. To suspect a diagnosis, it is necessary to carefully collect information about the course of pregnancy and childbirth, the pace of physical and mental development of the girl in the first years of life. As part of the comprehensive diagnosis of trisomy, the following research methods are used:
- Karyotyping. The study of the chromosome set is the only possible method of confirming the diagnosis. Such a study reveals signs of trisomy, makes it possible to distinguish between complete and mosaic forms of aneuploidy.
- Neurological examination. For early detection of cognitive disorders, speech and communication skills are checked, a comprehensive study of the level of motor development, a test for social functions is carried out. According to the indications, a consultation of a psychologist, a psychiatrist is appointed.
- Prenatal diagnosis. During pregnancy of a woman with confirmed X-chromosome tripling, it is advisable to study the karyotype of the fetus in order to confirm or exclude the presence of an additional chromosome in the child. This is performed by amniocentesis, cordocentesis.
In the absence of any manifestations of the syndrome in the patient, there is no need to prescribe therapy. The question of the expediency of medical supervision of such women remains debatable, although most experts advise them to undergo regular extended medical examinations to exclude complications of trisomy syndrome. Dutch scientist Martin Otter and American pediatrician Nicole Tartaglia proposed the following program of dispensary observation:
- In infancy — standard preventive examinations by a pediatrician and other specialists according to the schedule.
- In the preschool period — kidney ultrasound, EEG, checking the level of intellectual development, if necessary — speech therapy correction.
- In primary and secondary school age — a study of the functions of the sensory organs, extended tests on the level of socio-psychological skills, recommendations for additional classes with tutors, correctional teachers (if there are indications).
- In high school age, in addition to standard medical examinations, professional orientation is provided, taking into account possible features of mental development.
- In adulthood — in the absence of deviations, special examinations are not required.
Prognosis and prevention
Most women diagnosed with triple X syndrome lead a full life, realize their reproductive function and may not be aware of the existence of a genetic problem. The forecast is generally favorable. The syndrome does not cause life-threatening complications, does not shorten life expectancy. Given the absence of significant provoking factors, primary prevention of the disease is impossible.