The Down syndrome – chromosomal anomaly at which in a karyotype there are additional copies of genetic material on the 21st chromosome i.e. is observed a trisomiya on a chromosome 21. Phenotypical symptoms of a Down syndrome are presented by a brakhitsefaliya, a flat face and a nape, a Mongoloid section of eye cracks, an epikant, a skin fold on a neck, shortening of extremities, a korotkopalost, a cross palmar fold, etc. The Down syndrome at the child can be revealed prenatalno (according to ultrasonography, a biopsy a horiona, amniocentesis, a kordotsentez) or after the birth on the basis of external signs and a genetic research. Children with a Down syndrome need correction of the accompanying development violations.
Down syndrome - an autosomny syndrome at which the karyotype is presented by 47 chromosomes at the expense of the additional copy of a chromosome of the 21st couple. The Down syndrome is registered with a frequency of 1 a case on 500-800 newborns. The ratio of floors among children with a Down syndrome makes 1:1. For the first time the Down syndrome was described by the English pediatrician L. Daun in 1866, however the chromosomal nature and an essence of pathology (a trisomiya on a chromosome 21) was revealed nearly a century later. The clinical symptomatology of a Down syndrome is various: from congenital malformations and deviations in intellectual development to a secondary immunodeficiency. Children with a Down syndrome need additional medical care from various experts in this connection they make special category in pediatrics.
Down syndrome reasons
Normal cells of a human body contain 23 couples of chromosomes (a normal female karyotype 46,XX; men's - 46,XY). At the same time one of chromosomes of each couple is inherited from mother, and another – from the father. Genetic mechanisms of development of a Down syndrome are covered in quantitative violation of autosomes when additional genetic material joins the 21st couple of chromosomes. Existence of a trisomiya determines the lines characteristic of a Down syndrome by the 21st chromosome.
Emergence of an additional chromosome can be caused by genetic accident (not divergence of pair chromosomes in an ovogenesis or a spermatogenesis), violation of cellular division after fertilization or inheritance of a genetic mutation from mother or the father. Taking into account these mechanisms in genetics distinguish three options of anomaly of a karyotype at a Down syndrome: regular (simple) trisomiya, mosaicism and unbalanced translocation.
The majority of cases of a Down syndrome (about 94%) is connected with a simple trisomiya (a karyotype 47,XX, 21+ or 47,HY, 21+). At the same time three copies of the 21st chromosome are present at all cages owing to violation of division of pair chromosomes during meiosis in maternal or fatherly gametes.
About 1-2% of cases of a Down syndrome are the share of a mosaic form which is caused by violation of a mitosis only in one cage of the germ which is at a stage of a blastula or a gastrula. At a mosaicism the trisomiya of the 21st chromosome comes to light only in derivatives of this cage, and other part of cages has a normal set of chromosomes.
The translocational form of a Down syndrome occurs at 4-5% of patients. In this case the 21st chromosome or its fragment is attached (translotsirutsya) to any of autosomes and at meiosis departs together with it in again formed cage. Serve as most frequent "objects" of a translocation a chromosome 14 and 15, is more rare – on 13, 22, 4 and 5. Such reorganization of chromosomes can have casual character or be inherited from one of parents, being the carrier of the balanced translocation and having a normal phenotype. If the father acts as the carrier of a translocation, then the probability of the birth of the child with a Down syndrome makes 3% if the carriage is connected with maternal genetic material, the risk increases up to 10-15%.
Risk factors of the birth of children with a Down syndrome
The child's birth with a Down syndrome is not connected with a way of life, an ethnic origin and the region of residence of parents. The only authentically established factor increasing risk appearance of the child with a Down syndrome is the age of mother. So, if at women up to 25 years the probability of the birth of the sick child makes 1:1400, by 35 years already 1:400, by 40 years - 1:100; and to 45 - 1:35. First of all, it is connected with decrease in control of process of cell fission and increase in risk of not divergence of chromosomes. However, as the frequency of childbirth at young women in general is higher, statistically, 80% of children with a Down syndrome are born from mothers aged up to 35 years. According to some information, the age of the father is more senior than 42-45 years also increases risk of development of a Down syndrome in the child.
It is known that in the presence of a Down syndrome at one of uniovular twins, this pathology in 100% of cases will be available for another. Meanwhile, at nonidentical twins, and also brothers and sisters, probability of such coincidence it is insignificant it is small. Among other risk factors – existence in a family of persons with a Down syndrome, the age of mother is younger than 18 years, a translocation carriage one of spouses, the closely related marriages, casual events breaking normal development of gametes or a germ.
Thanks to performing preimlantatsionny diagnostics, conception by means of VRT (including an extracorporal opldotvoreniye) considerably reduces risk of the birth of the child with a Down syndrome at parents from risk groups, however completely does not exclude such opportunity.
Down syndrome symptoms
Incubation of a fruit with a Down syndrome is accompanied by the increased risk of an abortion: spontaneous termination of pregnancy happens approximately at 30% of women on the term of 6-8 weeks. In other cases children with a Down syndrome, as a rule, are born full-term, but have moderately expressed hypoplasia (body weight 8-10% lower than average). Despite various cytogenetic options of chromosomal anomaly, the typical external signs allowing to assume existence of pathology already at the first survey of the newborn neonatology are peculiar to most of children with a Down syndrome. At children with a Down syndrome all can be expressed or some of the physical characteristics described below.
80-90% of children with a Down syndrome have craniofacial dizmorfiya: the flattened face and a nose bridge, a brakhitsefaliya, a short wide neck, a flat nape, deformation of auricles; newborns – a characteristic skin fold on a neck. The person differs in a Mongoloid section of eyes, existence of an epikantus (a vertical fold of the skin covering an internal corner of an eye), a mikrogeniya, a half-open mouth often with full lips and the big put-out language (makroglossiya). The muscular tone at children with a Down syndrome is usually lowered; hyper mobility of joints (including atlanto-axial instability), deformation of a thorax takes place (keeled or funneled).
Mild extremities, brakhidaktiliya (brakhimezofalangiya), little finger curvature (klinodaktiliya), a cross ("monkey") fold on palms, wide distance between 1 and 2 fingers of feet (a sandalevidny crack), etc. are characteristic physical signs of a Down syndrome. At survey of children with a Down syndrome white spots on edge of an iris (Brushfild's spot), Gothic (the arc-shaped sky), the wrong bite, furrowed language come to light.
At translocational option of a Down syndrome external signs are shown more distinctly, than at a simple trisomiya. Expressiveness of a phenotype at a mosaicism is defined by a share of trisomny cages as a part of a karyotype.
At children with a Down syndrome more often than in population VPS (an open arterial channel, DMZhP, DMPP, Fallo's tetrad, etc.), squint, a cataract, glaucoma, relative deafness, epilepsy, a leukosis, defects of a GIT (a gullet atresia, a stenosis and an atresia of a duodenum, a disease of Girshprunga), congenital dislocation of a hip occur at others. Characteristic dermatological problems of the pubertatny period are dryness of skin, eczema, acne rash, follikulit.
Children with a Down syndrome treat often ill; they have children's infections heavier, have pneumonia, average otitises, a SARS, adenoides, tonsillitis more often. Weak immunity and congenital defects are the most probable cause of death of children in the first 5 years of life.
Most of patients with a Down syndrome has violations of intellectual development - as a rule, intellectual backwardness of easy or average degree. Motor development of children with a Down syndrome lags behind peers; the system underdevelopment of the speech takes place.
Patients with a Down syndrome are inclined to development of obesity, locks, a hypothyroidism, gnezdny alopetion, small egg cancer, an early onset of the illness of Alzheimer, etc. Men with a Down syndrome are, as a rule, infertile; fertility of women is considerably reduced in view of anovulyatorny cycles. Growth of adult patients is usually 20 cm lower than an average. Life expectancy makes about 50-60 years.
Diagnosis of a Down syndrome
For prenatal detection of a Down syndrome at a fruit the system of prenatal diagnostics is offered. Screening of the I trimester is carried out on the term of pregnancy of 11-13 weeks and includes identification of a specific ultrasonography signs of anomaly and determination of level of biochemical markers (HGCh, RARR-A) in the pregnant woman's blood. Between 15 and 22 weeks of pregnancy screening of the II trimester is carried out: obstetric ultrasonography, blood test of mother on an alpha fetoprotein, HGCh and . Taking into account age of the woman the risk of the birth of the child pays off with a Down syndrome (accuracy - 56-70%; false positive results - 5%).
Passing of prenatal invasive diagnostics is offered to pregnant women from risk group on the child's birth with a Down syndrome: biopsies of a horion, amniocentesis or a kordotsentez with a kariotipirovaniye of a fruit and consultation of the medical geneticist. At data acquisition for presence at the child of a Down syndrome the solution of a question of prolongation or termination of pregnancy remains for parents.
Newborns with a Down syndrome in the first days of life need a provdeniye of EhoKG, ultrasonography of an abdominal cavity for early detection of congenital malformations of internals; survey of the children's cardiologist, children's surgeon, children's ophthalmologist, children's traumatologist-orthopedist.
medico-pedagogical escort of children with a Down syndrome
Treatment of chromosomal anomaly is impossible today; any offered methods of treatment are experimental and have no the proved clinical efficiency. However systematic medical observation and the pedagogical help to children with a Down syndrome allow to achieve progress in their development, socialization and acquisition of labor skills by them.
Throughout all life patients with a Down syndrome have to be under observation of experts (the pediatrician, the therapist, the cardiologist, the endocrinologist, the otolaryngologist, the ophthalmologist, the neurologist, etc.) in connection with associated diseases or the increased risk of their development. At detection of heavy congenital heart diseases and a GIT their early surgical correction is shown. In case of the expressed decrease in hearing selection of the hearing aid is made. At pathology of an organ of vision-point correction, surgical treatment of a cataract, glaucoma, squint can be required. At a hypothyroidism replacement therapy by tireoidny hormones etc. is appointed.
For stimulation of development of motor skills the physical therapy, LFK occupations is shown. Occupations with the logopedist and oligofrenopedagogy are necessary for children for development of speech and communicative skills with a Down syndrome.
Training of children with a Down syndrome is, as a rule, carried out at special correctional school, however within the integrated education such children can attend also usual mass school. In all cases children with a Down syndrome belong to the category of children with special educational needs therefore need the additional help of teachers and social teachers, use of special educational programs, creation of the favorable and safe environment. An important role is played by psychology and pedagogical support of families where "solar children" are raised.
Forecast and prevention of a Down syndrome
Possibilities of learning ability and socialization of persons with a Down syndrome are various; they in many respects depend on mental abilities of children and on the efforts made by parents and teachers. In most cases children with a Down syndrome manage to impart the minimum household and communication skills necessary in everyday life. At the same time, cases of progress of such patients in the field of the fine arts, acting skills, sport, and also receiving the higher education are known. Adults with a Down syndrome can conduct independent life, seize simple professions, establish families.
It is possible to speak about prevention of a Down syndrome only from a position of reduction of possible risks as the probability of the birth of the sick child exists in any couple. Obstetricians-gynecologists advise women not to postpone pregnancy for late age. To predict the child's birth with a Down syndrome genetic consultation of families and system of prenatal screening is intended to help.