Is Down syndrome normal?

Down syndrome, or three body 2 1- syndrome, also known as congenital stupidity or Down syndrome, is a disease caused by chromosome abnormality (an extra chromosome 2 1). 60% of the children miscarried in the early fetus, and the survivors had obvious mental retardation, special face, growth and development obstacles and multiple deformities. The incidence of Down syndrome is related to the pregnant age of the mother. It is an abnormality of chromosome 2 1, and there are three types: trisomy, translocation and chimerism. Older pregnant women and aging eggs are important reasons for not separating.

clinical picture

1. The child has obvious special facial signs, such as wide eye distance, low nasal root, small eye fissure, oblique eyes, epicanthus, small external ear, fat tongue, frequent spitting and drooling. Short stature, smaller head circumference than normal people, short head back and forth diameter, flat head pillow. The neck is short and the skin is slack. Bone age often lags behind age, delayed teething and frequent dislocation. Hair is soft and less. The anterior fontanel closed late, and there may be a third fontanel in the occipital midline. The limbs are short, the joints can be excessively bent due to ligament relaxation, the fingers are thick and short, and the middle phalanx of the little finger is underdeveloped, which makes the little finger bend inward, the phalanx is short, and the trigeminal point of the palm shifts to the distal end. Palmprint and sandal foot are common, and about half of children with toe ball are arched dermatoglyphics.

2. It is often manifested as drowsiness and difficulty in eating, and its mental retardation is gradually obvious with the increase of age. IQ 25 ~ 50, delayed motor development and sexual development.

3. Male Down's baby will not have fertility until adolescence. A female Down's baby will have menstruation when she grows up and may give birth to a child.

4. Children are often accompanied by congenital heart disease and other malformations. Because of their low immune function, they are prone to various infections, and the incidence of leukemia is 10 ~ 30 times higher than that of the general population. If you live to adulthood, you will often have symptoms of Alzheimer's disease after 30 years old.

cheque

1. Karyotype analysis of peripheral blood cells

Cytogenetic studies have found that when chromosome 2 1 long arm is trisomy, the individual has completely similar clinical manifestations to Down syndrome. On the contrary, individuals who are not trisomy in this area do not have such typical symptoms. It can be inferred that 2 1q22 region may be the key gene region of Down syndrome, also known as Down syndrome region. According to karyotype analysis, children with Down syndrome can be divided into three types:

(1) standard type accounts for 95% of all cases. The child has 47 somatic chromosomes and an extra chromosome 2 1 with a karyotype of 47, XX (or XY), +2 1.

(2) The translocation type accounts for 2.5% ~ 5%, and the total number of children's chromosomes is 46, mostly robertsonian translocation, which refers to a mutual translocation of proximal centromere chromosomes, mostly D/G translocation. In group D, chromosome 14 is dominant, that is, the karyotype is 46, XX (or XY),-14, +T, and a few are 15. About half of the children with this translocation type are hereditary, that is, their parents have balanced translocation chromosome carriers. The other is G/G translocation, which is rare, because two chromosomes 2 1 in Group G have centromere fusion to form an isoparametric chromosome t(2 1q2 1q), or 1 2 1 translocation to1.

(3) Chimeric body type accounts for 2% ~ 4% of the disease. Children have more than two cell lines (the two most common), one is normal and the other is 2 1- trisomy cell. The severity of clinical manifestations is related to the percentage of normal cells, which can range from nearly normal to typical phenotype. The higher the proportion of 2 1- trisomy cell line, the lower the intelligence.

2. Chromosome examination of amniotic fluid cells

Chromosome examination of amniotic fluid cells is an effective method for prenatal diagnosis of Down's syndrome, and pregnant women with "high risk" screening results need to confirm whether the fetus is a child with Down's syndrome. At present, the most commonly used technology for prenatal diagnosis is amniocentesis, that is, under the guidance of B-ultrasound, the needle is inserted into amniotic fluid through the abdomen of pregnant women, and amniotic fluid is extracted for chromosome analysis of fetal cells. Suitable for 16 ~ 20 weeks pregnant women. In addition to amniocentesis, prenatal diagnostic techniques include villus biopsy, fetal umbilical vein puncture and fetal endoscopy. The common karyotype is the same as that of peripheral blood cells.

3. Fluorescence in situ hybridization

Using the corresponding sequence of chromosome 2 1 as a probe, three fluorescent signals of chromosome 2 1 can appear in the cells of patients with down syndrome by hybridization with lymphocytes or amniotic fluid cells in peripheral blood. If the specific sequence in the core region of Down syndrome fish is selected as a probe, the abnormal position of chromosome 2 1 can be accurately located, and the accuracy of detecting the number and structural abnormality of chromosome 2 1 can be improved.

4. Prenatal screening of serum markers

It has been explored for many years to screen Down's syndrome by measuring serum chorionic gonadotropin (HCG), alpha-fetoprotein (AFP) and free estriol (FE3) in pregnant women. Free estriol is an indicator of the second trimester of pregnancy (after 13 weeks).

According to these three serological indexes (HCG and AFP can also be measured) and the age and weight of pregnant women, the risk rate of children with Down syndrome can be calculated, and further diagnosis can be made according to the risk rate.

5. routine x-ray, ultrasound, electrocardiogram, EEG and other examinations.

Some children can find changes such as congenital heart disease, delayed bone age and abnormal EEG.

diagnose

Karyotype analysis and FISH technology: Although the special facial and hand features and mental retardation of the disease can provide important clues for clinical diagnosis, the establishment of diagnosis must depend on karyotype analysis, so karyotype analysis and FISH technology are the main laboratory examination techniques for Down syndrome. These two tests are also of positive significance for the prognosis estimation of Down syndrome chimera. Because of the great difference in phenotype, the clinical manifestations of chimera children can range from normal or nearly normal to typical, and their prognosis mainly depends on the percentage of normal cell lines in children's somatic cells. Therefore, understanding the ratio of normal karyotype cells to 2 1- trisomy karyotype cells in somatic cells of chimera children can guide their families and society to carry out education according to their specific conditions.

treat cordially

Because children's immunity is low, attention should be paid to preventing infection. If accompanied by congenital heart disease, gastrointestinal tract or other malformations, surgical correction may be considered.

prognosis

Infants and young children often have repeated respiratory infections, and those with congenital heart disease often die early. Muscle tension gradually improves with age, and the gap between growth and development progress and normal infants gradually increases. 15 years old, no longer tall, short stature, low IQ, mosaic type can reach more than 50%. The baby behaves like a "good boy". In childhood, most of them are cheerful and kind to people, but their emotional control ability is poor, fluctuating greatly, and sometimes they are quite stubborn and naughty. Comprehensive measures, including medical and social services, should be taken to educate and train patients patiently for a long time, prepare mentally retarded children for transition to ordinary schools, and train them to master certain work skills. After patient education and training, under supervision, people can take care of themselves and even do simple social work and stand on their own feet. Parents and schools should help children overcome behavioral problems, and society should give moral support to parents of disabled children.

prevent

There is no effective treatment at present. The best way is to terminate the pregnancy before the pregnant mother gives birth. The contents of prenatal prevention for pregnant women are as follows:

1. Genetic counseling

The older the pregnant woman, the higher the risk rate. The recurrence risk rate of standard Down syndrome is 65438 0%. Parents of children with translocation should carry out karyotype analysis in order to find balanced translocation carriers: if the mother is D/G translocation, the risk rate of each fetus is10%; If the father is D/G translocation, the risk rate is 4%. Most cases of G/G translocation are sporadic, and their parents' karyotypes are normal, but 2 1/2 1 translocation carriers are also found, and their next generation 100% suffers from this disease.

2. Prenatal diagnosis

This is an effective measure to prevent the birth of children with Down syndrome. Couples who have a history of bearing this disease should make prenatal diagnosis, that is, chromosome karyotype analysis. Sampling includes amniocentesis of amniotic fluid cells in the second trimester, chorionic villi cells in the second trimester and umbilical cord blood lymphocytes in the second trimester. The determination of serum markers HCG and AFP in prenatal screening has certain clinical significance, because it can reduce the blindness of prenatal diagnosis of amniocentesis, prompt the existence of high-risk pregnant women, enable these pregnant women to do further prenatal examination and consultation, and prevent the birth of children with Down syndrome to the greatest extent.