Down syndrome, also known as trisomy 21, is the most common chromosomal disorder caused by autosomal aberration. It is clinically characterized by intellectual disability, distinctive facial features, or other associated malformations. The reported incidence of this condition ranges from 0.1% to 1.5% internationally, while domestic surveys show rates of 2.36% in Shanghai (1979) and 2.11% in Harbin (1980).

bubble_chart Etiology

Chromosomal abnormalities are often associated with the following factors: advanced maternal age (over 35 years old), the last pregnancy in a multiple gestation, prolonged infertility, viral infections in early pregnancy, exposure to radiation, and certain medications. Translocation-type chromosomal abnormalities are more commonly seen in offspring of younger mothers.

bubble_chart Pathogenesis

The chromosomal changes in this disease can be divided into three types:

1. G group 21 trisomy According to foreign statistics, this type accounts for 92.5% of all affected children, while domestic data show it accounts for 88.5%. The total number of chromosomes in affected children is 47, with an additional chromosome 21. Since there are three chromosome 21s in the child's body, the genes carried are more than normal, disrupting the balance of genetic material in the body and causing abnormal fetal development.
2. Translocation type Foreign reports indicate that this type accounts for 4.8% of cases, while domestic reports show 3.1%. The total number of chromosomes in affected children is normal, at 46, with one being a translocation chromosome. The more common types are G/D translocation and G/G translocation: (1) G/D translocation type: The child's cells lack one D group chromosome (usually chromosome 14) and are replaced by a translocation chromosome, formed by the long-arm translocation of chromosomes 21 and 14, resulting in a 21/14 chromosome. Although the total number of chromosomes is normal, the genetic material is actually increased, leading to abnormal development in the child. (2) G/G translocation type: Two chromosome 21s in the G group undergo centromere fusion to form an isochromosome, or one chromosome 21 and one chromosome 22 translocate to form a new 21/22 chromosome.
3. Mosaic type Foreign reports indicate that this type accounts for 2.7% of cases, while domestic data show it accounts for 11.9%. Affected children have more than one karyotype in their bodies, with the clinically common form being mosaicism between a normal karyotype and 21 trisomy. The occurrence of mosaicism is mostly due to nondisjunction during the early division of the fertilized egg, resulting in some cells in the developing individual being normal and others being 21 trisomy cells.

bubble_chart Clinical Manifestations

The child exhibits intellectual developmental disorder, delayed physical growth, and distinctive facial features such as wide-set eyes, upward-slanting palpebral fissures, a flat nasal bridge, a partially open mouth, a tongue often protruding from the mouth, and excessive drooling, hence the term "tongue-protruding dementia." The muscle tone in the limbs is hypotonic, and due to ligament laxity, the joints may exhibit hypermobility. The little finger is short and curved inward. The child often presents with other malformations such as congenital heart disease, umbilical hernia, micropenis, and polydactyly. The child is prone to respiratory infections like pneumonia.
Dermatoglyphic changes: Despite karyotypic differences, children with this condition share common dermatoglyphic characteristics. Common dermatoglyphic features include unilateral or bilateral simian creases, a palmar triradius t displaced toward the center of the palm, an increased atd angle (often greater than 58°; the normal atd angle in Chinese populations is 41°), and approximately 80% exhibit tibial arch patterns on the hallux (the arch concavity facing the hallux side, Figure 12-1). Additionally, there is an increased frequency of ulnar loops on the fingers, often observed on all ten digits. These dermatoglyphic changes are closely related to chromosomal aberrations. Therefore, when chromosomal testing is unavailable, a relatively accurate diagnosis can be made based on dermatoglyphic features.

bubble_chart Auxiliary Examination

1. White Blood Cell Examination In this disease, the white blood cell count is normal, with hyposegmentation of granulocytes presenting as drumstick-shaped.
2. Enzyme Changes Superoxide dismutase and alkaline phosphatase are significantly elevated in the white blood cells of affected children.
3. Chromosome Examination The majority of affected children exhibit a trisomy 21 karyotype, with a minority showing G/D translocation, G/G translocation, or mosaicism.

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bubble_chart Diagnosis

The diagnosis of typical cases is not difficult based on distinctive facial features, intellectual disability, delayed physical development, and dermatoglyphic characteristics. However, chromosomal testing is required for confirmation. Most affected children have a simple trisomy 21 karyotype (47, +21), while a minority exhibit translocation types (21/14, 21/22 translocation) or mosaicism. Children with simple trisomy 21 or translocation types display typical clinical manifestations, whereas those with mosaicism show varying degrees of clinical severity depending on the proportion of abnormal cell lines.

bubble_chart Treatment Measures

1. Strengthen nursing and healthcare work and actively conduct training.
2. Acupuncture treatment: Acupuncture points include Dazhui (DU14), Yamen (DU15), Baihui (DU20), Yintang (EX-HN3), Neiguan (PC6), Hegu (LI4), and Zusanli (ST36). For those with unclear pronunciation and tongue protrusion, add Lianquan (RN23).
3. Medication treatment: Generally, try glutamic acid or γ-aminobutyric acid, thyroid tablets, vitamin B1, B6, etc.

bubble_chart Prognosis

The prognosis for pure 21 trisomy and translocation types is relatively poor. If one of the parents is a mosaic type, the prognosis depends on the proportion of abnormal cell lines, with a smaller proportion indicating a better prognosis.

bubble_chart Prevention

Take the following preventive measures to reduce the incidence of this disease:

1. Elderly women (over 35 years old, especially over 40 years old) should practice contraception.
2. Those with a family history of this disease should undergo early parental chromosomal karyotyping. If both parents have normal karyotypes, the recurrence risk rate is only 1%. If one parent is a translocation carrier, the recurrence risk rate increases significantly. When one parent is a D/G translocation carrier (if female, the offspring incidence rate is 5–10%; if male, 3–5%), the theoretical recurrence risk rate is 25%. If the carrier is a G/G translocation, 100% of their offspring will be affected. If confirmed as a D/G or G/G translocation carrier, contraception should be practiced, or amniotic fluid cell chromosomal testing should be performed during subsequent pregnancies. If the fetus has chromosomal abnormalities, the pregnancy should be terminated.
3. Mothers should avoid X-ray exposure and the misuse of chemical drugs before and during pregnancy, and prevent viral infections.