What are Chromosomal Abnormalities?

The chromosome is the basic substance that makes up the nucleus of cells, and is the carrier of genes. Chromosome abnormalities are also called chromosome dysgenesis. Chinese American Jiang Youxing (1956) identified 46 human chromosomes, and Caspersson et al. (1970) first published photographs of human chromosomal bands.

Chromosomal abnormality

The chromosome is the basic substance that makes up the nucleus of cells, and is the carrier of genes. Chromosome abnormalities are also called chromosome dysgenesis. Chinese American Jiang Youxing (1956) identified 46 human chromosomes, and Caspersson et al. (1970) first published photographs of human chromosomal bands.

Introduction to chromosomal abnormalities

Chinese American Jiang Youxing (1956) identified 46 human chromosomes as Caspersson et al. (1970) first published human chromosome bands

Photo from 1971

Chromosomal abnormalities

Since the Paris International Chromosome Naming Conference in 2014, more than 3,000 human chromosome abnormalities and structural aberrations have been discovered. At present, more than 100 chromosome disease syndromes have been identified. Mental retardation and growth retardation are common characteristics of chromosome diseases.

The most common chromosomal disorder, Down'ssyndrome, has a neonatal incidence of 1/700 to 1/600. With the exception of Down syndrome, trisomy13 syndrome (trisomy13syndrome) has a prevalence of 1 in 2,000 live births, more women than men, and the mother's average childbearing age is 31 years. Trisomy 18 syndrome (trisomy18syndrome) has a live infant incidence rate of 1 in 4,000 women, and the mother's average childbearing age is 34 years. Fragile-Xsyndrome is estimated to affect 1 / 1500th of a baby boy. Since a woman has two X chromosomes, the involvement rate is 50%. The chromosome phenotype of Klinefelter's syndrome is less severe. XXY, only seen in men. Turner syndrome has XO (45X) chromosomes and is only found in women. The incidence of newborns with Williams syndrome is 1/2 thousand, the incidence of newborns with Prader-Willi syndrome is 1/2 thousand, and the incidence of Rett syndrome is 1 / 1.5 to 10,000, only seen in women .

Causes and classification of chromosomal abnormalities

Causes of chromosomal abnormalities

The chromosome is the carrier of genes. Chromosome diseases are abnormal chromosomes, which leads to abnormal gene expression and abnormal development of the body. The pathogenesis of chromosomal aberrations is unknown, which may be caused by the chromosomes not separating at the later stage of cell division or the chromosomes breaking and reconnecting under the influence of various factors in vivo and in vitro.

1. Physical factors: human radiation environment, including natural radiation and artificial radiation. Natural radiation includes cosmic radiation, earth radiation, and radiation from human radioactive materials. Artificial radiation includes radiation and occupational radiation.

Ionizing radiation is striking because it causes chromosomes to not separate. Experiments have shown that comparing irradiated oocytes in the middle stage of MII with unirradiated contemporaneous oocytes, it was found that non-segregation was significantly higher in the irradiated group, and this phenomenon was particularly pronounced in older mice. Human lymphocytes were irradiated or grown in irradiated serum. It was found that the trisomy frequency of the experimental group was higher than that of the control group, and caused chromosomal aberrations such as dicentric chromosome ectopic and deletion.

2. Chemical factors: People are exposed to a variety of chemicals in daily life, some are natural products, and some are artificially synthesized. They will enter the human body through diet, breathing or skin contact, causing chromosomal aberrations.

3. Biological factors: When cells in culture are treated with viruses, they often cause many types of chromosomal aberrations, including breakage, pulverization, and interchange.

4. Maternal age effect: When the fetus is 6-7 months old, all oocytes have developed into primary oocytes, and entered the nuclear network phase from the first pre-meiotic stage, at which time the chromosomes loosely stretch again. It looks like a pronucleus and stays until ovulation during puberty. This state may be related to synthetic yolk. By puberty, due to the periodic stimulation of oocytes by FSH, only one polar body is completed per month. Secondary oocytes are excreted from the ovary, enter the fallopian tube, and undergo a second meiosis in the tube to reach the middle stage of division. At this time, if the fertilization occurs, the egg will complete the second meiosis and become a mature egg, which will combine with the sperm to become a zygote. From then on, new individuals will develop until delivery. With the increase of maternal age, under the influence of many factors inside and outside the mother, many aging changes may also occur in the egg, affecting the inter-relationship between the same pair of chromosomes in mature division and the actions of the later division, leading to the non-segregation between chromosomes.

5. Genetic factors: chromosomal abnormalities can often be expressed as familial tendencies, which suggests that chromosomal aberrations are related to heredity.

6. Autoimmune diseases: Autoimmune diseases seem to play a role in non-separation of chromosomes. For example, there is a close correlation between the increase of primary thyroid autoimmune antibodies and familial chromosomal abnormalities. ^[1]

Classification of chromosomal abnormalities

Quantitative aberrations include aneuploidy and aneuploidy aberrations, and the number of chromosomes increases, decreases, and triploids appear.

Structural aberrations: chromosomal deletions, translocations, inversions, insertions, duplications, and circular chromosomes can be divided into autosomal aberrations, such as Down (trisomy 21) syndrome Patau (trisomy 13) syndrome and Edward (trisomy 18) Syndromes, as well as sex chromosome aberrations such as Turner syndrome (XO) and congenital testicular hypoplasia.

The most common chromosomal disease Down syndrome pathological changes: patients with a brain weight of about 10% lighter than normal have only a simple brain gyrus structure, a small frontal lobe, a thin temporal superior gyrus, and white matter myelin forming late cortical neurons with hypoplasia and Low differentiation. Patients over 40 years of age can see Alzheimer's disease-like neurofibrillary tangles and senile plaques.

Clinical manifestations of chromosomal abnormalities

Down syndrome (Down'ssyndrome) is also called trisome21 syndrome (trisome21syndrome) and congenital fool type. This is the most common in humans

Chromosomal abnormalities

The incidence of neonatal chromosomal diseases is 1/700 to 1/600. The most common cause of mental retardation accounts for 10% of cases of severe mental retardation.

Seguin (1846) first reported the clinical manifestations of the disease. LangdoneDown (1866) gave a comprehensive description of the disease. British scholars later referred to the disease as Down syndrome. Lejeune et al. (1959) proved that the disease was caused by chromosome 21 The name ploidy caused and advocated for trisomy 21 was recognized at the Denver Conference in 1970.

In addition to Down syndrome, other chromosomal hypoplasias include Patau syndrome, trisomy 18, Criduchat syndrome, fragile X syndrome, circular chromosome syndrome, Klinefelter syndrome, Turner syndrome, Colpocephaly syndrome, Williams syndrome, Prader-Willi and Angelman syndrome, Rett syndrome, etc.

Chromosomal abnormality common syndrome

Down Chromosomal abnormality Down syndrome

The clinical characteristics of (Down'ssyndrome) are as follows: Children with Down syndrome have certain pathological characteristics at birth, and the symptoms become obvious with age. Craniofacial manifestations with rounded head and lower nose

Chromosomal abnormalities

Bone hypoplasia can cause the face to be flat, the mouth has a slightly stretched tongue, the body is hypertrophic and deeply cracked, and often sticks out of the mouth, so it is called tongue-like dementia. The epidermis of the palate often covers the part, and the palpebral fissures of the palate patients can be slightly tilted upwards and outwards to form a Mongolian-like shape. The ears are low in oval shape, and the ear lobe is small. Iris gray-white spots are known as Brushfield'sspots. ), The cardia closed obviously late.

Chromosomal abnormal dull syndrome

The average length of the child at birth is slightly shorter than that of a normal newborn, and the difference grows with age. The adult patient's height rarely exceeds that of a normal 10-year-old child. The hand is short and thick, and the width of the palm is only one horizontal line, showing horizontal palm folds (through the hand) and other characteristic skin lines. For example, the little finger is short and the internal flexion is a single fold (that is, the fifth finger is two sections) ), Most children with reduced muscle tone still cannot walk when they are 3 to 4 years old, infants and young children are slow to respond or can not lead to eating difficulties. The children's intelligence and mental development are significantly abnormal. The IQ is 20 to 70, with an average of 40 to 50 in the Gaussian curve. Below, 90% of children do not speak until they are 5 years old. Most are quiet, docile, and accessible, with life spans up to 40 years.

Some patients can see cataracts, congenital heart disease or secondary heart disease, cerebral embolism and brain abscess, gastrointestinal abnormalities such as duodenal stenosis, atlanto-axial joint instability, strenuous exercise can lead to spinal cord compression, and mesenchymal cells The incidence of lymphocytic leukemia is higher than that of ordinary patients in their 40s. Alzheimer's disease is almost universal, with inattention, taciturn speech, poor spatial orientation, poor memory, decreased judgment, and seizures.

13 Chromosomal abnormality trisomy 13

Trisomy 13 syndrome (trisomy13syndrome), also known as Patau syndrome, the incidence of live infants is 1/2000, more women

Chromosomal abnormalities

For men, the average childbearing age of the mother of the child is 31 years.

The patient presented with a protruding forehead, small eyes, corneal opacity with iris defect, olfactory loss, low cleft lip and palate, capillary aneurysm, polydactyly (toe) deformity, curved fingers, heel kyphotic right heart, umbilical hernia Children with hearing impairment, hypertonicity, and severe mental retardation often die early in childhood.

18 Trisomy 18

Trisomy18 syndrome (trisomy18syndrome) has a live infant incidence rate of 1/4000, which is more common in women. The mother's average childbearing age is 34 years.

The child presented with stunted growth, drooping upper eyelid, eyelid deformity, low ears, small mouth, small chin, and skin spots indicating that the fingers exceeded the middle finger and clenched a fist, deformity of the fingers (toes), and large and short rocker-bottomfeet toes , Ventricular septal defect umbilical hernia or inguinal hernia, short sternum, increased pelvic and muscle tone, occasional seizures, severe mental retardation, etc. often die in early infants.

Chromosomal abnormality meow syndrome

Meow syndrome (Criduchatsyndrome) is caused by the deletion of the short arm of chromosome 5.

The child's crying kittens appeared several weeks to months after birth, severe mental retardation, too much eye separation, epidermal folds (epicanthalfolds), short head deformities, full moon face, anti-congenital stupid eyelid distortion, Mandibular muscle hypotonia and strabismus.

X Fragile X syndrome

Fragile-Xsyndrome is a fragile site where the X chromosome is abnormal and easily broken. Martin and Bell (1943) first reported an X-linked inherited mental retardation family line. Lubs (1969) found that the X-chromosome length of this family patient There is a fragile site at the end of the arm, which confirms that there is an unstable inherited CGG repeat at this site. Normal humans have 43 to 200 repetitive sequences and more than 200 patients. The extra sequences can inactivate the gene encoding the RNA binding protein, affect protein expression and cause symptoms.

This syndrome is the most common cause of hereditary mental retardation and is estimated to affect 1/1500 boys. Since women have two X stains

Chromosomal abnormalities

Body, the involvement rate is less than 50%. It is estimated that more than 10% of male children with inherited mental retardation have abnormal fragile X chromosomes. Sometimes women are also affected but the disease is relatively mild. Rousseau et al. Described a simple and sensitive experimental method using DNA analysis technology during pregnancy and after birth. Diagnosis in children Because the length of the repeated triplet codon is related to the degree of mental retardation, the fragile X chromosome variant is occasionally found in men with normal intelligence, and the grandson of the patient may be sick. The child presents a typical triad: mental retardation, special features (such as long face, large ears, wide forehead, nose, wide and high bow), and large testes. The height of the children is normal, and the large testes generally appear at the age of 8 to 9 years. , 85% of children may have mental retardation, mostly moderate to often show behavioral abnormalities, mostly appear before puberty, common self-harmful behavior, hyperactivity and impulsive behavior, and stereotyped and weird movements, ADHD, polyphonia, Patients with autism may have seizures from 9% to 45% of children with unique claps. A DNA test can confirm the diagnosis. Ring chromosomes: Ring chromosomes (ringchromosome) are manifested as mental retardation accompanied by various physical deformities.

Klinefelter Klinefelter syndrome

Klinefelter's syndrome (Klinefelter'ssyndrome) has a chromosome phenotype of XXY and is only found in men. The patient is tall and behaves like a testis-free person. Shoulder width, thinning hair and body hair, high pitch, feminization of the breast, and reduced testicular muscle tone are usually accompanied by mental retardation but to a lesser extent. The disease is complicated by asthma and endocrine disorders. Such as with diabetes is more likely.

Turner Turner syndrome

The chromosome of Turner syndrome is XO (45X) type only found in women. The patient has a short neck with a webbed face and a triangular shape. The nipples of the small inferior chin are wide. The elbow is bent with fingers (toes) and hypoplasia of the nails. It may be accompanied by the folding of the inner ridges of the palate, which may be sexually retarded and moderate. Degree of mental retardation and so on.

Colpocephaly Colpocephaly syndrome

Colpocephaly syndrome is a rare brain malformation, many of which are caused by chimerism of chromosome 8 and are often misdiagnosed as various types of ventricular dilatation with abnormal brain development. Patients present with mental retardation, spasticity, and seizures

Chromosomal abnormalities can be detected

Dysplasia leads to significant dilatation of lateral ventricular occipital angles such as visual abnormalities, thickening of cortical gray matter edges, and thinning of white matter.

Williams Chromosomal abnormalities Williams syndrome

Williams syndrome is a small deletion in the elastin gene region on chromosome 7, with a prevalence of 1/2 million in newborns. Williams first described that it is unclear whether there are characteristic lesions in the brain. There was a case reported in the 35-year-old On biopsy of the patient, no brain abnormalities were found except for changes in Alzheimer's disease.

The patient's mental retardation is relatively light, the precocious music ability can have amazing memory of the score, and the symphony can be remembered after listening to it; some patients can write large sections of descriptive text with correct wording and content, but it will not depict simple Children with developmental delays have unique appearances, such as: wide mouth, almond eyes, upturned holes, and small and pointed ears. They are called "goblin-like" appearances; they have a gentle personality and are sensitive to auditory stimuli. Visual space and athletic deficits. There may be cardiovascular malformations such as aortic stenosis.

Prader-WilliAngelman Chromosomal abnormalities Prader-Willi and Angelman syndrome

The incidence of Prader-Willi syndrome in newborns is 1/2 000. The prevalence of both sexes is caused by the deletion of chromosome 15 q11-q13. Cytogenetic analysis and DNA analysis can be used to detect 70% of cases of chromosomal defects. It is caused by the non-hereditary deletion of the paternal X chromosome.

The child presented with decreased muscle tone, disappeared tendon reflexes, short stature, deformed face, and obvious genital developmental disorders. At birth, there may be joint flexion. After 1 year, obvious mental retardation or hypomentia may occur. obesity.

Angelman syndrome is caused by deletion of q11-q13 of chromosome 15. Unlike Prader-Willi syndrome, this disease is caused by a single genetic defect in the maternal line.

Prenatal check can be prevented

Children with depression show severe mental retardation, microcephaly, and early seizures. They are not sensitive to antiepileptic drugs, and have rare marionette-like postures and movement disorders. They often want to laugh or smile like old, "happy Puppet syndrome. "

Rett Rett syndrome

Rett syndrome was first described by Rett (1966). The etiology is unknown. It is dominant on the X chromosome. Some people speculate that metabolic mechanisms are involved in the incidence of disease. , Often unable to survive.

If it is a female, normal hand development is lost at birth and early in the postnatal period 6 to 15 months. Later, the ability to communicate is lost, the body is retarded, and the head is enlarged. Exercise, ataxia gradually appears and lower limb rigidity eventually loses walking and speech ability. Paroxysmal hyperventilation and breath hold, normal nocturnal breathing rhythm, and seizures can occur.

This disease can be misdiagnosed as Kanner's loneliness syndrome. The difference between the two is that Rett syndrome loses its ability to exercise early, loses focus and loses joint eye movements.

Chromosomal abnormalities

There are many types of chromosomal abnormalities, the clinical symptoms and signs are complex and diverse, and the manifestations outside the nervous system are different. For details, please refer to the clinical manifestations of each disease.

Chromosome abnormality

Mainly based on the child's characteristic symptoms, signs and chromosome examination. A chromosomal abnormality can be confirmed. Down syndrome caused by Trisomy 21 and the clinical manifestations of Down syndrome caused by chromosomal translocation are difficult to distinguish. There is a strong correlation between the two. It is related to the age of the mother. Mothers of children with Trisomy 21 are usually older at birth, but The incidence of chromosomal translocations is lower in older or younger pregnant women. Down syndrome subtypes, such as chimeric, some cells have normal chromosomes and some are abnormal. Chimeric patients may have the typical manifestations of Down syndrome, and some patients have normal intelligence.

Chromosomal abnormality test

Laboratory tests for chromosomal abnormalities

Down syndrome serological examination showed decreased serotonin, alkalinity in white blood cells, increased phosphatase, increased red blood cell diphosphate glucose, and 50% increase in peroxide dismutase, but it was not related to the patient's abnormal development and mental retardation.

About one-third of mothers with Down syndrome have increased serum alpha-fetoprotein content and increased serum chorionic gonadotropin content in the 4 to 6 months of pregnancy.

Prenatal inspection is key

High and decreased estriol levels may indicate fetal Down syndrome results. Positive pregnant women should undergo amniocentesis to detect patients' amniotic fluid cells or chromosomes.

Other auxiliary examinations for chromosomal abnormalities

Amniocentesis can be used to detect abnormalities of chromosomes in amniotic fluid cells and to screen children with Down syndrome and other chromosomal hypoplasia early.

Chromosome examination can use fluorescent insitu hybridization technology (fluorescentinsituhybridizationtechnique) to detect amniotic fluid cells or chromosomes of patients, such as Down syndrome can be found on chromosome 21 is triploid.

Treatment and prevention of chromosomal abnormalities

Treatment of chromosomal abnormalities

Treatment of chromosomal abnormalities is unsatisfactory, and there is no effective medicine for the treatment of congenital mental retardation. Traditional Chinese medicine treatment and rehabilitation training can be tried.

Prenatal examination of chromosomal abnormalities

Different types of chromosomal hypoplasia have different prognosis. Most of them have poor prognosis, mental retardation and growth retardation, which are the common characteristics of chromosomal diseases. Prevention of chromosomal dysplasia is difficult. The prevention of dissatisfaction is more important. Preventive measures include the implementation of genetic counseling, chromosome testing, prenatal diagnosis, and selective abortion to prevent the birth of children. Pregnant women should have regular prenatal check-ups. If there is a problem with the fetus, at least it can be detected early. The diagnosis of amniotic fluid pumping is one way to test whether a fetus has a congenital chromosomal defect.

Chromosomal abnormality related data

Karyotypes are named as follows: 46, XY for normal males, 46, XX for normal females. Trisomy 21 (Down's syndrome) due to an additional chromosome 21 (trisomy 21), the karyotype is named male 47, XY, + 21; the female is named 47, XX, + 21. Chromosomal translocation It can also cause trisomy 21. The mother of a typical 14/21 balanced translocation carrier writes 45, XX, t (14q; 21q). The translocation chromosomes are from 14q and 21q (on this chromosome, q is long Arm), short arm (p) has been lost. Short-arm deleted chromosome 5 (also known as 5p deletion syndrome), female karyotype is 46, XX, 5p-.

The incidence of chromosomal abnormalities in live babies is about 0.5%. Those with chromosomal abnormalities can be diagnosed prenatally. However, invasive prenatal diagnostic methods have more disadvantages than advantages. Therefore, prenatal diagnosis is only used in high-risk groups.

The advanced age of pregnant women is the most common indicator of prenatal cytogenetic diagnosis. Although chromosomal abnormalities can be found in pregnant women of all age groups, the incidence of trisomy karyotypes increases with age, and appears after 35 years of age. Exponential increase (Table 247-1), the reason is unknown so far. Due to spontaneous abortion, the incidence of fetal chromosomal abnormalities detected at 16-18 weeks of pregnancy is 30% higher than that of surviving newborns, and those who are over 35 years old should be born. Prenatal diagnosis. However, the age limit is relative, and younger women can also consider prenatal diagnosis.

Maternal serum abnormality markers suggest that the fetus has an increased risk of trisomy 21 and trisomy 18, and may be considered for amniocentesis (see below). Children with abnormal chromosomes are an indication for prenatal diagnosis. If one The couple already has a surviving child trisomy 21, and the childbirth age is under 30 years of age, then the risk of reborning a trisomy 21 fetus is about 1%. For people over 30 years old, they are pregnant with a trisomy 21 fetus again The risk is related to the actual age of the pregnant woman (Table 247-1). The table assumes that the patient does not carry a couple with Robertson translocation, and the data is limited to other trisomy karyotypes, but the risk of another chromosomal abnormality in the offspring increases by about 1%. Abnormalities (such as 45, X; triploid; new rearrangements) do not increase the risk of the next pregnancy. For couples who do not have an increased risk, if they have concerns, they can make a prenatal diagnosis.

A couple may have a child with a phenotypic abnormality but unknown chromosomal status. Phenotypic abnormalities are usually associated with chromosomal abnormalities. This situation occurs in 30% of live babies and in normal dead babies. 5% chromosomal abnormalities. If the abnormality of the previous child is due to abnormal chromosomes, there are indications for prenatal diagnosis.

Chromosomal abnormalities in parents increase the risk of chromosomal abnormalities in offspring. Balanced recombination in parents includes translocations (Robertson or swap translocation) and inversions (intra-arm and inter-arm inversion). They often have a normal phenotype but should be genetically counseled. And consider prenatal diagnosis. Autosomal aneuploid couples are rare. In theory, about 50% of the offspring of aneuploid parents are also aneuploid. But the mother is a trisomy 21, whose The incidence of trisomy in offspring is 1/3. Those whose father is trisomy 21 are infertile. Trisomy of sex chromosomes (such as 47, XXY) is very common and they are often accompanied by decreased fertility. Parents whose offspring are aneuploid are rare. Any couple with aneuploidy or fully chimeric chromosomes should be diagnosed prenatally. Couples with chromosomal abnormalities usually have multiple spontaneous abortions or offspring. Or a diagnosis of the cause of infertility.

Repeated spontaneous abortions often indicate chromosomal abnormalities. At least 50% of the early spontaneous abortions of fetuses have chromosomal abnormalities; about 1/2 of them are triploids. If the first aborted fetus is aneuploid, the reborn abortion may also be aneuploid. Ploidy, but this abnormality may not occur on the same chromosome. Trisomy (such as trisomy 16) pregnancy may be fatal and often lead to miscarriage, but phenotypic abnormalities and other trisomies (such as trisomy 18) may occur in another pregnancy. Live babies). People who have had a history of aneuploidy live births have an increased risk of re-pregnant aneuploidy live babies. However, whether aneuploidy recurrent spontaneous abortion increases the aneuploidy The risk of infants is still unclear. Some geneticists believe that recurrent spontaneous abortion should be used as an indication for prenatal diagnosis; if necessary, chromosomal recombination tests for both spouses

Causes of chromosomal abnormalities

Causes of chromosomal abnormalities 1. Men may also cause embryonic chromosomal abnormalities: Long-term use of drugs by men can affect sperm quality and cause adverse effects on the fetus. Under normal circumstances, there is a protective layer between the testicular tissue and the blood flowing through the testes, which is medically called the blood-testis barrier. This barrier prevents certain substances in the blood from entering the testes. However, many drugs can pass the blood-testis barrier and affect the healthy combination of sperm and eggs. For example, some common immunomodulators and other drugs have strong toxic effects and can directly disrupt the synthesis of sperm DNA, including changes in genetic material components, chromosomal abnormalities and sperm abnormalities. Like male infertility, women's habitual abortion (early embryo loss) is partly the result of male sperm damage.

Causes of chromosomal abnormalities 2. These drugs can also be excreted into the vagina with semen produced by the testicles through the vaginal mucosa, and then enter the blood circulation after absorption through the vaginal mucosa, increasing the incidence of low birth weight infants and malformed fetuses, increasing the risk of perinatal fetuses. mortality rate. Therefore, in the 2 to 3 months before pregnancy and during pregnancy, the husband must be careful with medication, unless there is a problem of chromosomal abnormalities in the husband and wife. If you have such doubts, it is recommended that both husbands and wives receive blood to check for chromosomal abnormalities.

Causes of chromosomal abnormalities 3. The first three months of pregnancy are a high-risk period of miscarriage. This spontaneous abortion is mostly caused by fetal chromosomal abnormalities and is a natural elimination. If it is not the natural elimination of fetal chromosomal abnormalities, but the miscarriage caused by the pregnant woman's own problems, the fundamental solution is to find out the problem and prescribe the right medicine to avoid another abortion. Atrophic eggs and hydatidiform moles are caused by chromosomal abnormalities of the fetus: atrophic eggs, hydatidiform moles = atrophic embryos. The cause of atrophic eggs is mostly the problem of the embryo itself.

^[2]

World's first abnormal chromosome

A rare human abnormal chromosome was found in Jiangxi. This chromosome was experimentally identified and was the first discovery in the world. So, how is this abnormal chromosome formed?

Jiangxi Maternal and Child Health Hospital recently discovered a rare abnormal human chromosome karyotype from a 3-year-old boy: 46, XY, dup (4) (p12p16). According to Li Yuzhong, a technician in charge of the hospital's prenatal diagnosis center, this abnormal chromosome was identified by the State Key Laboratory of Medical Genetics in China and was the first discovery in the world.

According to Li Yuzhong's analysis, this chromosome may be generated during meiosis by non-equivalent exchange between homologous chromosomes or non-equivalent exchange between chromatids. Depending on the degree of pathogenicity of the gene, patients may have congenital non-progressive mental retardation, growth retardation, and multiple deformities such as facial features, extremities, skin lines, and internal organs. ^[3]