What is Down syndrome? Causes of Down's Syndrome

Down syndrome is a disease caused by a chromosomal defect. This disease occurs mostly because the patient's mother is older when giving birth and the egg cells are aging.

Down syndrome is a chromosomal defect, also known as "down syndrome", and is one of the first syndromes combined with mental retardation. Down syndrome is caused by gene abnormality. The chromosome 21 of the affected child changes from the normal 2 to 3, so it is also called "trisomy 21 syndrome". It is one of the most common birth defects in my country.

Most children with Down syndrome have severe intellectual disabilities and other problems, such as leukemia, gastrointestinal malformations, etc. They cannot take care of themselves and have a short life span. The average survival age is only 20-30 years old, and the IQ is generally between 20-50.

The incidence of Down syndrome is related to the mother's age during pregnancy. It is an abnormality of chromosome 21 and has three types: trisomy, translocation and mosaicism. Older pregnant women and aging eggs are important causes of non-disjunction. Therefore, women who want to get pregnant should do so as early as possible. The older a woman is when she becomes pregnant, the greater the risk of having a fetus with Down syndrome.

The cytogenetic characteristic of Down syndrome is trisomy of chromosome 21, which occurs mainly because chromosome 21 does not separate during meiosis of the reproductive cells of one of the parents to form gametes, or during mitosis of the fertilized egg. Since most children with monosomic disease cannot survive, only trisomic offspring can be born. An extra chromosome 21 is present in the embryonic cells.

The pathogenesis is mostly related to the aging of oocytes caused by the advanced age of the pregnant woman; 5% are caused by the father. Only a very small number of cases are familial (one of the parents is a DS patient), in which the germ cells form secondary nondisjunction during meiosis. Since male patients with Down syndrome cannot have children, there is no problem of genetic offspring.