Down syndrome is a condition in which a person has an extra chromosome. Chromosomes are small "packages" of genes in the body. They determine how the baby's body develops during pregnancy and after birth, and how it forms and functions. Normally, a baby is born with 46 chromosomes. Babies with Down syndrome have an extra copy of one of these chromosomes, chromosome 21. In this article, we discuss the types of Down syndrome and its symptoms, how to diagnose, screening tests, diagnostic tests, treatment methods, and other health problems in these people. A medical term for having an extra copy of a chromosome is "trisomy". Down syndrome is also known as trisomy 21. This extra copy changes how the baby functions. The body and brain are growing, which can cause mental and physical challenges for the child. People with Down syndrome usually have a mildly to moderately low IQ and speak more slowly than other children. ### Some common physical characteristics of Down syndrome include: - Flat face, especially the bridge of the nose - Almond-shaped eyes that slant upwards - A short neck - Small ears - Tongue that tends to come out of the mouth - Tiny white spots on the iris (colored part) of the eye - Small hands and feet - a line across the palm (palm crease) - Little pinky fingers that sometimes bend towards the thumb - Weak muscle tone or loose joints in children and shorter adults Types of Down syndrome **There are three types of Down syndrome. People often cannot tell the difference between each type without looking at the chromosomes because the physical characteristics and behaviors are similar.** **1.Trisomy 21:**About 95% of people with Down syndrome have trisomy 21.2. With this type of Down syndrome, each cell in the body has 3 separate copies of chromosome 21 instead of the usual 2 copies. **2. Translocation Down syndrome:** This type includes a small percentage of people with Down syndrome (about 3%). This happens when there is an extra part or a whole extra chromosome 21, but it is attached or "trans" to a chromosome 21. A different chromosome instead of being a separate chromosome 21. **3. Mosaic Down syndrome:** This type affects about 2% of people with Down syndrome. Mosaic means mixture or composition. For children with mosaic Down syndrome, some of their cells have 3 copies of chromosome 21, but other cells have the normal two copies of chromosome 21. However, they may have fewer characteristics of this condition due to the presence of some (or many) cells with a normal number of chromosomes. Down syndrome diagnosis methods There are two basic types of tests to diagnose Down syndrome during pregnancy: screening tests and diagnostic tests. A screening test can tell a woman and her health care provider whether her pregnancy has a lower or higher chance of developing Down syndrome. Screening tests do not provide an absolute diagnosis, but they are safe for the mother and the developing fetus. Diagnostic tests can usually tell if a baby has Down syndrome, but they can be more dangerous for the mother and the developing baby. Neither screening nor diagnostic tests can predict the full impact of Down syndrome on the baby. No one can predict this. Down syndrome treatment methods Down syndrome is a lifelong disease. Early life services often help infants and children with Down syndrome improve their physical and intellectual abilities. Most of these services focus on helping children with Down syndrome to develop to their full potential. These services include speech, occupational, and physical therapy and are usually provided through early intervention programs in each state. Children with Down syndrome may also need extra help or attention at school, although many children are included in regular classes.