21-Three syndrome, also known as congenital dysgenesis or Down syndrome (Down’s syndrome), is the earliest and most common autosomal disorder identified in humans. The etiology is related to maternal gestational age, genetic factors, use of chemical abortions during pregnancy, radiation exposure, autoimmune diseases and viral infections. The incidence is about 1/(600-800) in live births, i.e. 1.6-1.2 per 1,000, and increases with maternal age. The karyotype analysis can be divided into three types: 1. Standard type, accounting for about 95% of the total number of affected children, is due to the non-separation of chromosome 21 in the germ cells of the parents (mostly mothers) during meiosis, resulting in an extra chromosome 21 in the body cells of the affected children, with a karyotype of 47, XY (or XX), +21. The parents’ karyotype is mostly normal, and only a very small number of them are inherited in the family (the mother is a 21-trisomy patient). 2. -The total number of chromosomes is 46, one of which is the long arm of the extra chromosome 21 and the long arm of a proximal chromosome with mitotic chromosomes, i.e., the reciprocal translocation of the proximal mitotic chromosome, called Robertson translocation, also called mitotic fusion. There are two types of D/G translocations and G/G translocations: (1) D/G translocations: the most common, with chromosome 14 predominating in group D. The karyotype is 46, XY (or XX), -14, +t (14q21q) and a few are chromosome 15 or 13. About half of this translocation phenotype is hereditary, i.e., expect to have 14/21 balanced translocation chromosome carriers with karyotype 45, XX (or XY), -14, -21, +t (14q21q). (2) G/G translocation: the majority of this type of translocation is the fusion of two chromosomes 21 chromosomes to form equal arm chromosomes, karyotype 46, XY or (XX), -21, +t (21q22q) 3, chimerism This type accounts for about 2-4%, due to the formation of chromosome 21 in the fertilized egg during early division does not separate the existence of the affected child The karyotype is 46, XY (or XX)/47, XY (or XX), +21. The proportion of abnormal cells in this type of child varies in clinical symptoms. Clinical features: 1. Mild or moderate, mostly moderate mental retardation, whose intelligence gradually decreases with age, from 1 to 10 years, while their average intelligence quotient (IQ) decreases from 58 to less than 40. Some experts also believe that IQ is relatively stable during adolescence before decreasing later. Most studies have shown that environmental factors are important in influencing IQ, and that patients raised in good environments have relatively high IQs. The degree of mental retardation can vary from one type of patient to another, with trisomies generally being the most severe and translocations the next most severe. Among the translocation types, those with equilibrium translocation have less intellectual involvement. As the children are quiet and docile, they provide better conditions for special education training. Although it is difficult to reach the level of elementary school grade 1-2 in cultural skills, there can be significant improvement in adaptive ability and a certain degree of self-care and labor ability; 2. Language development disorders: the average age of children starting to learn to speak is 4-6 years old, 95% have articulation defects, slurred speech, stuttering, low voice; more than 1/3 have 3. Behavioral disorders: most of them have mild temperament, often giggle, like to imitate and repeat some simple actions, can perform simple labor, a few patients are irritable, capricious, hyperactive, and even have destructive and aggressive behaviors, some show a tendency to cower, accompanied by posture of catatonia; 4. The difference between the motor function of the child and that of a normal child of the same age may not be significant for a period of time after birth, but the difference increases with age. Motor development also varies widely among patients. Patients with congenital dysfunction can perform simple movements, such as dressing and eating, but their movements are clumsy, uncoordinated, and their gait is unstable; 5. At birth, the height is l~3cm shorter than normal newborns, the head circumference is basically normal, the biparietal diameter is in the normal range, the anterior-posterior diameter is relatively short, and the occipital area is flat. Most of them have a short head shape. The fontanelle and forehead sutures are wide and close late, and the third fontanelle (the sagittal suture above the posterior fontanelle is widened) often appears. Children with this disease sleep deeply for a few days after birth, sucking and swallowing very slowly, or even completely unable, so it is very difficult to wake up and feed. The child has a short stature, the bone age lags behind the actual age, the teething is late and the sequence is abnormal; 6. The corners of the eyes are slanted upward, the eyes are far apart, the inner corners of the eye fissures are canthal, and the eyes are nystagmus. The nasal bridge is low and flat, and the nostrils are upturned. The mouth is small, the mouth is half open, the palate arch is high, the lips are thick, the tongue is often sticking out of the mouth, often giggling and looking foolish. The ears are small and round, with low ear position; 7, there may be through hands (50%); palm trigeminal point t shifted to the palm, atd angle increased (greater than 58 °, normal people less than 45 °) 8, the 5th finger some only a finger then fold lines; 9, 80% of the affected children generally low muscle tone, low muscle tone of the limbs short ligaments loose, the joints can be overly bent; 10, the hand is wide, thick, thick and short fingers, especially short pinky, pinky The middle and last phalanges are dysplastic, and the end of the little finger is often bent inward. The middle phalanges are short and wide and bent inward. The thumb is distant from the remaining four fingers; 11. Small pelvis is common. Unilateral or bilateral rib absence; 12. Short and wide dorsal neck; 13. Enlarged abdomen, often accompanied by separation of the rectus abdominis muscle, umbilical hernia; 14. May be accompanied by congenital heart disease, digestive tract malformations; 15. Prone to respiratory infections, blepharitis; 16. The incidence of congenital hypothyroidism and acute lymphoblastic leukemia is significantly higher than normal population; 17. External genital development is generally normal, but boys may have 18. High rate of Alzheimer’s disease after the age of 40, prone to memory loss, persistent low cognitive ability, personality changes and other symptoms. Treatment options There is no effective treatment available, and emphasis should be placed on training and education of the affected child. Children with Down’s syndrome who have early intervention will have an average IQ of about 17 points higher than those who do not have it by the age of 9-10. The principle used is physical rehabilitation using external stimuli to enable the child to fully develop his or her highest genetic intelligence. This training should begin immediately after birth. Screening: Early pregnancy screening items: PAPP-A (pregnancy-associated plasma protein-A), β-hCG (human chorionic gonadotropin) Mid-pregnancy screening items: AFP (alpha-fetoprotein), β-hCG (human chorionic gonadotropin), μE3 (free estriol), Inhibin-A (inhibin-A) Non-invasive DNA: By collecting 5mL of peripheral blood from pregnant women, extracting The risk rate of fetal chromosome aneuploidy, i.e. trisomy 21 (Down syndrome), trisomy 18 (Edward’s syndrome) and trisomy 13 (Patau’s syndrome), can be accurately determined by using next-generation high-throughput sequencing technology combined with bioinformatics analysis. The best time to test is between 12-24 weeks of pregnancy. The characteristics are non-invasive, no risk of miscarriage, high sensitivity; detection rate of more than 99%, is currently the safest and most accurate means of detection, no harm to both mother and baby. Amniocentesis: After amniotic fluid is extracted by amniocentesis, these cells are separated by centrifugation and then analyzed for chromosomes. If a family member has a definite genetic disorder, the genetic fragments of that disorder can be analyzed to determine if the disorder is present. The best time to get tested is from 12-16 weeks of pregnancy. Features a definitive test, but since it is an invasive test, the possibility of intrauterine infection.