Down syndrome is one of the most common genetically determined congenital diseases. It occurs in approximately one of 1,000 pregnancies.
The essence of the syndrome is a supernumerary chromosome number 21 in the cells of the affected individual. Normal healthy person's cells have 46 chromosomes arranged in 23 pairs. People with Down syndrome have a total of 47 chromosomes, including three chromosomes 21. The cause is a chromosomal disorder in the sex cell of the father (sperm), or mother (egg). It was found out that the main risk factor is the mother's age. It is logical - the longer the woman lives, the greater is the risk of genetic defects in her eggs. In twenty years old mother, the risk of a child with Down syndrome is about 1:1,500, while it is 1:25 in forty-five years old woman. As you can see, the difference is huge.
Note: There is also a rarer form of Down syndrome (to be more accurate, the so-called Robertsonian translocation of chromosome 21), when a certain chromosomal abnormality is present in every cell of the parent's body and not only in the sex cells. The parent itself is healthy, but has a high risk that his or her descendants will suffer from Down's syndrome. In such case, the Down syndrome has a familial occurrence.
Excessive amount of genetic information leads to complex manifestations. Individuals with Down syndrome are capable of survival, but they suffer from a number of pathological symptoms.
People with Down syndrome have smaller lower jaw and flat nose. Their eyes are slanted by a skin fold; the mouth is small with a large tongue. The figure is lower than in healthy people of the same age. The palm of their hand has just one single major line that is called "simian crease". The affected suffer from mild to moderate mental retardation; their IQ rarely rises above the level of 70 points. Most, however, are able to communicate, learn the basic social habits and they are educatable. Fertility is markedly reduced in the patients, but they are not always completely infertile.
For more serious medical complications, it is necessary to mention frequent occurrence of underactive thyroid, a relatively frequent occurrence of congenital heart defects and increased risk of leukemia during the life of the patient. They are more threatened by epileptic seizures and in older age, they are more frequently affected by Alzheimer's disease.
Diagnosis and prevention
The only prevention is detection of the affected fetus and its abortion. Down syndrome is one of the main medical reasons of abortion. The pillars of diagnostics are the pregnancy screening tests. These procedures include medical examinations, ultrasound examinations and blood tests (used to determine concentration of certain substances in mother's blood) to evaluate the approximate risk of Down syndrome in the particular child. If the risk is too big, the doctors may try to take a sample of amniotic fluid (amniocentesis), which contains cells of the fetus, or to obtain a sample of cells from chorionic villi of the placenta. The obtained cells are examined, including the number of chromosomes. These measures diagnose the vast majority of cases of Down syndrome.
Due to mental retardation, patients with Down syndrome require more attention and parental care than healthy children. An assistance of special education centers is usually necessary. Any congenital heart defects are solved by cardiac surgery and visible deformations may be treated by plastic surgeons.