The link between the facial characteristics and mental deficiencies of Down Syndrome was first recognized by John Langdon Down, an English physician, in 1866.
In 1959 Dr. Jerome Lejeune, a French physician, discovered that Down Syndrome was a result of a chromosomal abnormality.
Science
Our cells are made up of 46 chromosomes. We receive 23 chromosomes from each parent. A child with Down Syndrome has received an extra chromosome, meaning that their cells have 47. The additional chromosome is found in the 21st pair. It is not known what causes this extra chromosome, but it happens for 1 in 800 babies (depending on which source you read). It is a Syndrome that affects babies from all races, countries and economic statuses. Nothing that the mother does directly results in a baby with Down Syndrome. It is NOT hereditary.
It becomes more of a possibility for a woman to have a baby with Down Syndrome if she is over 45 years old at the time of birth. However, it is more common for younger women since they have higher fertility rates. There is also a slight trend in the age of the father, but it is more likely that the extra chromosome comes from the mother.
Types of Down Syndrome
The main cause of Down Syndrome is extra material in chromosome 21. However, there are three different types of Down Syndrome, based on the presentation of that extra material.
95% of children with Down Syndrome have non-disjunction Trisomy 21, which means that they have 47 chromosomes instead of the normal 46. They have an extra chromosome 21.
3-4% of children have translocation. This means that the extra chromosome material has attached onto another chromosome. The material is usually found attached to the 14, 21, or 22 chromosomes. When a child has translocation, the chance of having another child with Down Syndrome is increased. This is also the only form of Down Syndrome that can be passed onto offspring.
1% of children have mosaicism. In this condition, some cells have 46 chromosomes, others have 47.
Other Titles
Down Syndrome; Down's Syndrome; Downs Syndrome- the most common title, it can be written in three different ways, based on the website or book you are reading.
Trisomy 21- named this because of the occurrence of the third chromosome on the 21st pair. There are other occurrences of trisomy, which means that there is a third chromosome. This is the most common trisomy and the only one with a positive life expectancy. Trisomy 13 and Trisomy 18 children only have a 5% chance of surviving past the first year of life.
Mongolism- one of the first names that Down Syndrome was known as, since the babies resembled the people of Mongolia. This term is now considered to be a derogatory terms and should be avoided.
Descriptors
It is very easy to determine whether or not a child has Down Syndrome. There are several physical characteristics which are typical with these babies. However, not all traits are visible in every case of Down Syndrome and they are not a definitive diagnosis. The only definitive way of determining whether your child has Down Syndrome is to perform a karyotype, which is a test that shows a display of the chromosomes. Babies with Down Syndrome have: * reduced muscle tone- it is very easy for these children to gain weight and it is important to be in control of their diet * flat facial profile and nasal bridge with a small nose- the most common visual trait * eyes that slant up and out- often there is an epicanthic fold, which is a piece of skin that crosses the inner corner of the eyes * small mouth and large tongue- this accounts for many of the speech impediments that children with Down Syndrome have; however speech therapy is very helpful in overcoming this * space between first and second toe- often called "sandal gap" * broad hands with short fingers- about 50% of children have only one crease across the palm * below average birth weight and length- this accounts for the shorter stature of most children with Down Syndrome
Health Problems
There are some health problems associated with Down Syndrome, although these are NOT definite for each child and many children with Down Syndrome have no health problems at all. * many babies are born with heart defects, some which require surgery * hearing and sight problems * thyroid disorder * poor immune system * respiratory problems * obstructed gastrointestinal tract
The life expectancy of children with Down Syndrome have increased dramatically in response to better medical care and increased access to this care. Those with Down Syndrome now live to be 60-65 or older, which is an improvement from the past where children would not live to see their teenage years.