Chromosomal diseases

August 12, 2017 17:51 | Genetic Diseases

Chromosomal disease - syndromes whose development is due to changes in the number or structure of chromosomes.The frequency of chromosomal diseases among newborn babies is around 1%.Gross chromosomal abnormalities incompatible with life, and are a common cause of spontaneous abortions, miscarriages and stillbirths.When spontaneous abortion revealed about 20% of embryos with abnormal chromosome.There are a group of chromosomal diseases characterized by changes in the sex chromosomes and nonsexual chromosomes - autosomes.By sex chromosome abnormalities include Turner's syndrome (45, X0), Klinefelter's syndrome (47, XXY), trisomy X syndrome (47, the XXX), as well as more rare variants.

emergence of sex chromosome abnormalities due to their nondisjunction in meiosis or divisions in the early development of the zygote.As a result of non-disjunction of sex chromosomes are one of the sperm may have 22 autosomes and both sex XY-chromosome (male and female), the other sperm have only 22 autosomes.Also, when no

ndisjunction of sex chromosomes, the formation of eggs, containing 22 autosomes and two female X chromosome and only 22 autosomes.Theoretically, Turner's syndrome, a set of sex chromosomes XO may occur when the fertilized egg of normal sperm, contains no sex chromosome, or a fertilized egg containing no sexual chromosome bearing sperm in a set of female X chromosome.When a fertilized egg with two X chromosomes of the sperm with the X chromosome is formed trisomy syndrome X. The appearance of Klinefelter syndrome occurs when the fertilized ovum with the X chromosome sperm containing the X and Y-chromosome.

more complex sex chromosome abnormalities may be associated with fertilization with two X chromosomes, the sperm carrying the X and Y-chromosome, and so on. D. The cause of complex anomalies are also non-disjunction of sex chromosomes in the process of formation of gametes andin the early stages of division of the zygote.The overall frequency of sex chromosomes for anomalies in stillbirths was 2.7%, which is 25 times higher than among infants.

sex chromosome abnormalities

Turner Syndrome Shereshevskogo- (monosomy X)

first woman with a complete absence of menstruation, lack of development of secondary sexual characteristics and low growth has been described by N. Shereshevskii in 1925. In 1938 XXTurner has published data on 7 women with short stature, delayed puberty, absence of menstrual dysfunction, infertility, and wing-fold in the neck.

The frequency of Turner's syndrome is 1 in 3000 newborn female children.This is significantly less than the theoretically expected results, due to a high rate of spontaneous abortion.However, many embryos die in the early stages of pregnancy.

Newborn girls with Turner syndrome have expressed Shereshevskogo- swelling, located mainly on the back surface of the hands and feet.Such swelling usually disappear after a few months after birth.There have excess skin and increased mobility in the neck.As we age, it becomes clearly noticeable child stunting.A small growth of the girls combined with normal body proportions, although the child's appetite may be increased.Half of the girls appreciable short neck with pterygium skin fold.Externally, these children face looks mature enough, and features a body at the same time do not correspond to the intended age (infantile figure).On the skin there are dark spots may appear white spots (vitiligo), peripheral nerve tumors (neurofibromas), vascular tumors (hemangiomas).

Some girls with Turner syndrome may experience a variety of skeletal abnormalities: barrel or less flat chest, the fusion of the vertebrae together, cleft in the spine, bending stop inside (with respect to the median line of the body), short bones of the wrist and tarsus.Often you will notice a variety of tooth deformation.The internal organs characteristic manifestation of the syndrome are various congenital malformations of the cardiovascular system.The most characteristic feature is a coarctation of the aorta.Also, quite often in girls with careful examination in the hospital reveal stenosis of the aorta and pulmonary artery, ventricular septal defect.Quite often, there is an increase in blood pressure that may be due to aortic coarctation and concomitant renal development.For some children there may be bleeding from the gastrointestinal tract.By the time of puberty, signs of lag in sexual development (sexual infantilism).At the same time the breast is absent or adipose tissue, widely separated nipples and underdeveloped, body hair on pubis and armpits rather meager.External genitals are underdeveloped.The vagina is a long, narrow.The uterus is reduced in size.An integral feature of Turner's syndrome is the complete absence of menstruation, but some girls can be scarce rare menstruation.

Children lag behind in intellectual development.Decreased interest in the opposite sex.Logical thinking is limited.Girls are not critical to their existing defect.They usually complacent, hardworking differ complaisance.Feature syndrome Turner is complete proyavlyaemosti children hereditary diseases transmitted linkage with the X-linked type.Such diseases include hemophilia, myopathy, color blindness.

When X-ray systems detect bone ossification delay even at a mature age.Observed spinal deformity - kyphosis, scoliosis, shortening vertebral osteoporosis.When special survey methods revealed hypoplasia of the ovaries.In biochemical studies in the urine there is an increase in hormones that appear during puberty.Contents of female sex hormones in urine decreased.

study chromosomes in girls with Turner's syndrome reveals the 45 chromosomes: 22 pairs of autosomes and one X chromosome.Another characteristic feature is the absence of sex chromatin in the nucleus of a skin cell.The sex chromatin (Barr body) is present in most normal somatic cell nuclear girls.

believed that Turner's syndrome is more likely due to nondisjunction of sex chromosomes during the formation of sperm than eggs.

some of the girls with Turner syndrome Shereshevskogo-, who did not reveal the sex chromatin in the cells of the skin, can be determined by the male set of chromosomes 46, XY.Pathological changes in this case due to the lack of activity of male Y-chromosome, which outwardly appears as a set of sex chromosomes XO.Such a state of underdevelopment of gonads observed in girls with normal growth, with varying degrees of puberty.When stored in a certain degree of activity of the male Y-chromosomes of patients outwardly look like boys, have dwarfism with certain somatic changes, shortening the neck, small undescended testicles.Intelligence of the boys lowered.These are people with so-called male Turner's syndrome.In rare cases, people with a lack of sex chromatin in the cells of the skin (hromatinotritsatelnye person) found a mosaic chromosomal complement XO / XY, t. E. In certain somatic cells contain a sexual female X chromosome, in other X-and Y-chromosome.This syndrome is found in girls with underdeveloped gonads, in boys with undescended testicles, as well as in children with hermaphroditism.The peculiarity of this type of syndrome is a high incidence of tumors of the reproductive glands.

All of the above options for Turner's syndrome with chromosome sets CW 46, XY, XO / XY are hromatinotritsatelnymi, t. E. In all these cases, the body cells (somatic cells), particularly in cells of the skin, do not reveal genderchromatin.Along with this condition are described hromatinpolozhitelnye (sex chromatin is determined in the skin), the frequency of which is about 4 times less than the first.In some individuals as a result of genetic testing two female X chromosomes have been identified, but one of them was morphologically altered: the loss of part of a chromosome, ring X chromosome.Often found mosaicism XO / XX, when some cells have two X chromosomes, while others - one X chromosome.Signs of the disease in these people are less pronounced than in the XO syndrome: swelling at birth and webbed neck fold are observed in some cases, growth may remain normal, more often there are spontaneous menstruation.The ovaries can not be changed.Barr body (sex chromatin) with mosaicism detected, but in smaller amounts than in healthy girls.Mosaicism on sex chromosomes can be combined with the loss of part of the X chromosome.

Sometimes there are people with a set of sex chromosomes XO / XX / XXX.Outwardly, this type of mosaicism seen different variants of Turner's syndrome.When mosaicism XO / XX / XXX in the nuclei of the calf skin cells Barr no or one - two cells.When mosaicism XO / XXX sex chromatin is completely absent or is contained in a minimal amount.Manifestations of such a state is a swelling of the lymph nodes, wing-fold of skin on the neck, changes in the internal organs are detected less frequently.Gonads are usually underdeveloped.

Another type of mosaicism at hromatinpolozhitelnom Turner's syndrome is characterized by a ring of female X chromosome.Externally, these girls remind individuals with chromosome set XO / XX.Turner's syndrome, in which the nuclei of cells is determined by sex chromatin can be combined with small sex chromosomes, one of which is a normal X chromosome combines with another small sex chromosome.The girls revealed hypoplasia of gonads, underdevelopment.In the study of chromosomes and detect different combinations of sex chromosome abnormalities.

All individuals with Turner syndrome are identified characteristic changes in the skin patterns of the fingers and hands, which are determined by the method of fingerprinting.

to confirm the disease is necessary to study sex chromatin and chromosome set in a specialized hospital.Indications for such studies in boys are mild secondary sexual characteristics, and undescended testicles underdevelopment, low growth and reduced intelligence.

For the treatment of this syndrome used hormonal drugs, the use of female sex hormones advisable after discontinuation of growth.In the case of an earlier application of female hormones can prematurely stop growth.hormonal treatment course is 6-12 months.By increasing the effective treatment of the mammary glands appear menstruation, after which the dose of hormones decrease.

Klinefelter Syndrome

syndrome was first described in 1942 X. B. Klinefelter, who noted the characteristic symptoms of the disease: underdevelopment of the testicles in males increase the mammary glands, lack of development of the external genitalia and increased urinary excretion of FSH.In 1956, on the part of those with Klinefelter syndrome have found sex chromatin, after which Barr suggested division hromatinpolozhitelny syndrome (defined as sex chromatin) and hromatinotritsatelny (when the sex chromatin is not defined).The frequency of Klinefelter syndrome is 1 in 400 newborn boys.Among mentally retarded children Klinefelter syndrome occurs in 1-2% of cases.

Typically Klinefelter syndrome boys have high growth, sleep poorly, quickly get tired, characterized by a narrow thorax, marked breast enlargement, lack of testicles in the scrotum.However, these symptoms are usually found only in the period of puberty.Benign enlargement of the mammary glands and the absence of testicles in the scrotum are found in about half of boys with Klinefelter's syndrome, so recognition of this syndrome at an earlier age presents considerable difficulties.For many boys during puberty is characterized eunuchoid body proportions.The testes are small, soft to the touch, education disrupted sperm.When urine research on hormones reveal characteristic changes.

In some cases detected deformation of teeth, finger splice together various anomalies of the skeleton.Characteristic changes in the respiratory, cardiovascular and digestive systems can not be detected.Endocrine disorders are often represented by female type obesity, benign enlargement of the mammary glands, underdeveloped penis and testicles.Often boys determined female type of hair distribution.A feature of the syndrome is the high frequency of breast cancer: a 60-fold higher than in the population.

In some cases, may detect signs of damage to the nervous system:. Pupils inequality (anisocoria), decreased muscle tone, irregularities in the implementation of co-ordinatornyh samples, etc. In individuals with the syndrome Klinefelter described disorders of the brain, which manifest bouts of epilepsy.Significant changes are detected in the mental sphere.In some of the boys in the degree of dementia observed retardation, others retained normal intelligence.There is a decrease in mental activity, inability to long-term stress.A notable feature of Klinefelter syndrome is the extreme variability of symptoms from apparently normal individuals, with enough safe intelligence, to patients with syndrome and retardation.A common feature of the disease is the formation of a different degree of impairment of sperm and testicular hypoplasia, changes in hormone levels in the urine.Proyavlyaemost certain diseases linked to the X chromosome (color blindness, hemophilia and others.) Streets with Klinefelter syndrome lower than in healthy boys.

in 1959 was described by chromosome set of people with Klinefelter syndrome - 47, XXY.A characteristic feature of the chromosome set was the presence of an extra X chromosomes (22 pairs of autosomes and two X and one Y-chromosome).The presence of extra X chromosome causes various disorders in Klinefelter syndrome.In a significant number of skin cells found sex chromatin.All individuals with this syndrome have a male phenotype (appearance), hypoplasia of the testes syndrome, debility.With an increasing number of X-chromosome (which may also be 3, and 4) the degree of reduction increases intelligence, a tendency to the formation of defects.

the treatment of Klinefelter's syndrome, hormonal drugs are used.Positive results of the treatment of benign breast enlargement can be obtained during surgery.

trisomy syndrome X

patients with trisomy girls for sexual X chromosome is detected chromosomal complement of 47 chromosomes (47, XXX).The frequency of trisomy X syndrome is 1 in 1200 newborn girls.This syndrome can manifest decline of intelligence in mild, menstrual disorders or complete absence of menstruation.Often trisomy X syndrome does not manifest itself outwardly.This girl may be able to bear children.It is interesting to note that in mothers with trisomy X are born normal children.

much less common syndrome with four sex chromosomes: 48, XXXX.Such girls typically found mental retardation.The syndrome 49, XXXXX degree of reduction of intelligence deeper.Patients girls have dwarfism, various congenital malformations.