Pediatric Down syndrome

Introduction

Introduction to Children's Down Syndrome

Down syndrome, or trisomy 21syndrome, is also known as congenital or Down syndrome. It is the earliest identified chromosomal disease. 60% of children have abortion in the early stage of the fetus, and the survivors have obvious intelligence. , special face, growth and development disorders and multiple deformities.

basic knowledge

Sickness ratio: 0.0001%

Susceptible people: children

Mode of infection: non-infectious

Complications: congenital heart disease

Pathogen

The cause of Down's syndrome in children

Cause:

The incidence of Down syndrome is related to the age of maternal pregnancy. It is an abnormality of chromosome 21, and there are three types of trisomy, translocation and chimerism. The mother age is high, and egg aging is an important cause of non-segregation.

(two) pathogenesis

The three-body type can be isolated from the chromosome 21 of the meiotic phase of the parental germ cell. The mechanism of the three-body type is due to the fact that the germ cells of the parent (mostly the mother) are not separated when the meiosis occurs. The pregnant woman is older. The greater the likelihood of Down's syndrome (Table 1), the chimeric 21-trisomy cell line and maternal parental germ cells found in a family study of normal diploid parents' 21-trisomy The single parental dimer of chromosome 21 is also responsible for the occurrence of 21-trisomy. The translocation type can be inherited by one of the parents for the chromosome 21 translocation carrier. In addition to the chromosomal translocation, the peripheral blood lymphocyte karyotype of the parents Most of the normal, the key part of chromosome 21 that produces the phenotypic characteristics of Down's syndrome is 21q22.1~q22.2, and the 21 parts of the trisomy that do not include this zone do not present Down syndrome.

Prevention

Prevention of Down Syndrome in children

There is currently no effective treatment. The best way is to terminate the pregnancy before the pregnant mother produces it.

Prenatal prevention for pregnant women:

Genetic counseling

The older the pregnant woman, the higher the risk rate. The risk of recurrence of standard Down's syndrome is 1%. Parents of translocation children should be karyotyped to find carriers with balanced translocations: if the mother is D/G translocation, each fetus has a 10% risk rate; if the father is a D/G translocation , the risk rate is 4%. The vast majority of G/G translocation cases were sporadic, and most of the parental karyotypes were normal, but 21/21 translocation carriers were also found, and the next generation of 100% suffer from this disease.

2. Prenatal diagnosis

It is an effective measure to prevent the birth of children with Down syndrome. Couples with a history of birth of the disease should be prenatally diagnosed, that is, karyotype analysis, sampling includes amniocentesis in the second trimester for amniocentesis, embryonic villous cells in the second trimester, and cord blood lymphocytes in the second trimester. Prenatal screening for serum markers HCG and AFP has certain clinical significance because it can reduce the blindness of amniocentesis for prenatal diagnosis, suggesting the presence of high-risk pregnant women, allowing these pregnant women to undergo further prenatal care and counseling. Minimize the birth of children with Down syndrome.

Complication

Complications of Down syndrome in children Complications congenital heart disease

Often accompanied by congenital heart disease; due to low immune function, susceptible to various infections; the incidence of leukemia is 10 to 30 times higher than the general; male is often cryptorchidism; still visible with strabismus, nystagmus, tracheoesophageal fistula, Umbilical hernia, duodenal atresia, thyroid disease, etc., occasionally seizures.

Congenital cardiovascular disease is the most common type of congenital malformation. Light asymptomatic, when examined, found that severe cases may have difficulty breathing after breathing, purpura, syncope, etc., older children may have growth retardation.

Symptom

Symptoms of Down Syndrome in Children Common Symptoms Dementia Neck Short Mental Disorders Rogue Eyes Wide Bone Ages Delayed Tumor Closure Late Through Cleft Palate in the Clubuxeps... Brain Development Slow

The child has a distinct special face at birth, and often presents with difficulty in sleepiness and feeding. The mental retardation of the child is gradually increasing with age. The IQ is about 25-50, and the development of the athletes and sexual development are delayed. Wide, low nose, low eye crack, oblique outer side of the eye, inner suede, small outer ear, fat tongue, often protruding out of the mouth, more drooling, short stature, head circumference less than normal, short front and rear The occipital flat is flat, the neck is short, the skin is loose, the bone age is often behind the age, the teeth are delayed and often misplaced, the hair is soft and less, the hair is more centered, the front squat is closed, and the top line of the top pillow can have a third. Tuen, short limbs, due to ligament relaxation, joints can be excessively curved, short fingers, small bones in the little finger dysplasia, small inward bending, short phalanx, palm three-point shift to the distal end, common through palm print, grass shoes About half of the children with the ball of the big toe have an arched pattern.

Children often have other malformations such as congenital heart disease. Because of low immune function, they are prone to various infections. The incidence of leukemia is 10 to 30 times higher than that of normal. If you live to adulthood, it usually appears after 30 years old. Symptoms of senile dementia.

Examine

Examination of children with Down syndrome

1. Analysis of karyotype of peripheral blood cells

According to the karyotype analysis, children with Down syndrome can be divided into 3 types:

(1) Standard type: The children's somatic chromosomes are 47, with an additional chromosome 21, with a karyotype of 47, XX (or XY), +21, which accounts for 95% of all cases.

(2) Translocation type: about 2.5% to 5%, the total number of chromosomes in children is 46, mostly Robertsonian translocation, which refers to a mutual translocation occurring in the proximal centromere chromosome. Mostly D/G translocation, the D group is mainly chromosome 14, ie the karyotype is 46, XX (or XY), -14, +t (14q21q); a few are chromosome 15 translocations, this kind About half of the translocation children are hereditary, that is, the parents have balanced translocation chromosome carriers, and the other is G/G translocation, which is rare because of the centromere of two chromosomes in group G. Fusion, forming an isobaric chromosome t (21q21q), or a 21 translocation to a chromosome 22.

(3) Chimera type: about 2% to 4% of the disease, there are 2 or more cell lines in the child (more common in 2), one is normal, the other is 21-three Somatic cells, the severity of clinical manifestations are related to the percentage of normal cells, ranging from near normal to typical phenotypes. The higher the proportion of 21-trisomy cell lines, the heavier the degree of mental retardation and deformity.

Cytogenetic studies have found that when the 21q22 region of the long arm of chromosome 21 is a trisomy, the individual has a clinical manifestation that is completely similar to Down's syndrome. On the contrary, individuals with non-trisomy in this area have no typical symptoms. It is inferred that the 21q22 region may be a key region of Down's syndrome gene, also known as Down's syndrome.

2. Amniocentesis chromosome examination

Amniocentesis chromosome examination is an effective method for prenatal diagnosis of Down's syndrome. The common karyotype is the same as the karyotype of peripheral blood cells.

3. Fluorescence in situ hybridization

Using the corresponding sequence of chromosome 21 as a probe, hybridize with lymphocytes or amniocytes in peripheral blood. The cells of Down's syndrome can display the fluorescence signals of three chromosomes 21, if Down syndrome is selected. The specific sequence of the core region is used as a probe for FISH hybridization analysis, which can accurately locate the abnormal part of chromosome 21 and improve the accuracy of detecting chromosome 21 number and structural abnormality.

4. Prenatal screening for serum markers

The use of maternal serum chorionic gonadotropin (HCG), alpha fetoprotein (AFP), and free estriol (FE3) for the screening of Down's syndrome has been explored for many years. This is a mid-pregnancy indicator (13 weeks). In the future, according to the three (and can also measure HCG and AFP) serological indicators as well as the age and weight of the pregnant woman, the risk rate of children with Down syndrome is estimated, and the diagnosis is further carried out according to the risk rate. About 60% of Down's syndrome fetuses can be detected by this method. The diagnostic value of pregnancy-associated plasma protein A (PAPP-A) has been paid more and more attention in recent years. PAPP-A is produced by placental trophoblast cells. The serum level of pregnant women in the fetus is significantly reduced, presumably related to the trophoblast cell function decline, which is an early pregnancy screening index, suitable for pregnant women 8 to 14 weeks pregnant screening, using PAPP-A, HCG, AFP Such index screening can not only screen Down syndrome, but also detect 18-trisomy syndrome, congenital neural tube defects, congenital abdominal wall defects and other congenital anomalies. In addition, the skin thickness of fetal neck is measured by B-ultrasound. Is an important indicator of diagnosis of Down syndrome, therefore, early pregnancy, pregnant women to carry out mid-term Down's syndrome screening, early take active preventive measures, there is a certain significance in ensuring the health of women and children.

X-ray films, ultrasound, electrocardiogram, EEG, etc. can be routinely performed. Some children may have congenital heart disease, bone age, and abnormal EEG.

Diagnosis

Diagnostic identification of children with Down syndrome

diagnosis

The special face of the disease, the characteristics of the hand and the low intelligence can provide important clues for clinical diagnosis, but the establishment of the diagnosis must rely on karyotype analysis, so karyotype analysis and FISH technology are the main laboratory of Down syndrome. Examination techniques, these two tests also have positive implications for the prognosis of Down's syndrome chimeric, due to the disparity in phenotypes in children with chimeric abnormalities, ranging from normal or near normal to typical clinical manifestations, their prognosis It depends mainly on the percentage of normal cell lines in the somatic cells of the child. Therefore, the proportion of normal karyotype cells and 21-trisomy nucleus cells in the somatic cells of chimeric children can be understood, and the children can be guided according to their specific conditions. The family and society educate them.

Differential diagnosis

The disease should be differentiated from congenital hypothyroidism. The latter can have drowsiness, crying hoarseness, feeding difficulties, abdominal distension, constipation and other symptoms after birth. The tongue is large and thick, but there is no special face of this disease. Serum TSH, T4 and karyotype analysis were identified.

Congenital hypothyroidism is caused by a congenital defect in the thyroid gland or due to iodine deficiency in the diet during pregnancy. The former is called sporadic thyroid dysfunction, and the latter is called endemic hypothyroidism. Its main clinical manifestations are physical and intellectual developmental disorders. It is a common endocrine disease in children.

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