Down syndrome is a genetic abnormality, in most cases without a developmental abnormality: the cells of the patient contain three copies of chromosome 21 instead of two copies.
Down syndrome is characterized mainly by a specific facial structure associated with mental retardation of various degrees. The visible signs of the disease include a flat face, slanted eyes, set wide apart, with the so-called Mongol lid in the eye corners, depressed nose root, small nose and projecting ears, palmar crease, with extra space between and second toe, and short limbs.
Mental retardation is often associated with other developmental diseases, such as heart problems, sensory and digestive abnormalities. As regards babies with Down syndrome, the risk of spontaneous miscarriage is higher for healthy babies, while the newborns need special care, sometimes for their entire life. All these constitute a significant burden for the family, so screening for Down syndrome or detecting the disease at an early gestational stage is very important.
Without preventive tests, this abnormality would occur in approximately 1 in 600-700 newborns. The disease is not hereditary in 95% of the cases, which means that it can occur even if there is no family history of this problem. Incidence increases with age.
The incidence of Down syndrome increases with the age of the mother. For this reason, women over 35 years old are routinely screened in Hungary. However, there is no routine screening for those below 35 years of age, so most cases with Down syndrome (about 70%) occur in these young mothers.