What is down syndrome?
Down syndrome or trisomy-21 is a birth defect that is associated with mental retardation, typical external characteristics and certain medical problems, and which is caused by the genetic material from chromosome 21 occurs in triplicate (instead of in duplicate).
The syndrome occurs in about 4.6 of every 10,000 births in all populations. Analogous conditions are also found in other species, such as chimpanzees.
Down syndrome causes
People who have this syndrome, the DNA of all genes which are located on chromosome 21 too much in all (or many of) their body cells. As a result, in these cells, all sorts of proteins produced in excess. For example, one of these is the beta-amyloid precursor protein APP (peptidase nexin-II), which plays a role in the etiology of Alzheimer's disease. The excess chromosome 21 can occur in three ways:
- In 95% of cases it is referred to as Trisomy-21. That is, that there is in every cell three instead of two copies of chromosome 21 are present. Usually in the formation of the gametes, the egg, there are two chromosomes 21 instead of one in the core come, because the two chromosomes at meiosis not from each other losraakten 21 (non-disjunction). After fertilization there were thereby three. On aging of the OVA is significantly more frequently for this derogation. On advanced maternal age increases the risk of giving birth to a child with trisomy-21 significantly. The risk of having a child with Down syndrome on maternal age 25 is 1 in 1250; at age 30 is 1 in 1000; at age 35 is 1 in 400; at age 40 is 1 in 100; at age 45 is 1 in 30. However, although the chances of a child with Down syndrome is greater in older mothers, most children with this syndrome are born from young mothers. There is also a low correlation with the age of the father.
- At 4% of the Down-patients, there is a ("unbalanced") translocation of chromosome 21. Here too, there is a third chromosome 21 is present in every cell, but this is not loose in the nucleus, but am stuck on chromosome 14, or there are two chromosomes 21 together. It is also possible that the father or mother had a "balanced" translocation. Sat with him or her than any of the chromosomes, chromosome 14 or 21 to 21 were two chromosomes to each other. However, where the total number of copies of chromosome 21 in each cell nucleus two remains, is there with a "carrier" itself usually nothing to worry about. However, their children are at a high risk of Down syndrome (at 14/21 translocation 1: 3 and 1: 3 will carry; a 21/21 translocation carrier will only children with Down syndrome can get). In most cases, however, the parents are not a carrier and is the translocation in the formation of the germ cells arise for the first time. Several dozen families are traced in Netherlands with carriers that do not have Down's syndrome. Children of carriers can also carry without that they know or brands.
- In 1% of cases there is mosaicism for chromosome 21; that is to say that only a part of the cells has a third chromosome 21. This disorder arises from one of the first cell divisions in the early embryo, in that the doubled chromosome 21 to the cell division is not detached from each other (non-disjunction).
Down syndrome symptoms
Feature
- Mental disability
- Epica Thus Tuck eyes (round corner of the eye)
- Almond-shaped, slightly slanting eyes
- Atypical facial shape
- Flat back
- Slack, resembling large tongue and mouth open
- One transverse, continuous hand fold
- Often a missing joint of the ring finger
- Often a larger space between the large- and adjacent toe
- In about 40 to 50 percent of cases, a congenital heart defect
- In 60 to 70 percent of cases, prenatal screening a smaller / no nasal bone visible on ultrasound
- Hyperlaxity (flaccid ligaments, muscles and joints)
- Often short stature
- Often smooth, thin hair
- Shorter life expectancy (70 years and older is fairly rare).
Medical problems
People with Down syndrome have a higher risk of getting these diseases. For a person or counselor who assists an individual with the syndrome, it is therefore important to consider complaints to the following conditions:
- Intellectual disability varies from very mild to very severe. Only a very small minority have normal to high IQ.
- Approximately 40 to 50 percent have a congenital heart defect; usually an opening in the septum between the ventricles (ventricular septal defect), the atria (atrial septal defect) or on the border of atria and ventricles (atrioventricular septal defect). When this heart defect is substantial and is not corrected surgically, occurs later in life chronic oxygen deficiency with all its consequences.
- At birth, there may be construction of disorders of the esophagus, duodenum or anus.
- Patients with Down syndrome have a less well-functioning immune system and run a higher risk of acquiring infections. So they run after a hepatitis B infection more likely to be carriers of the virus. This is one reason for the recommendation to vaccinate all newborns with Down syndrome to the hepatitis B virus.
- Are also common skin problems, such as types of eczema (atopic dermatitis, seborrheic dermatitis), or athlete's foot.
- In childhood, there is an increased risk of leukemia.
- Thyroid problems (too slow or too fast acting) are common in Down syndrome.
- Eye problems (eg, cataracts, myopia, keratoconus) are more common in Down syndrome.
- Many people with Down syndrome are hearing impaired.
- Atlanto-axial instability (instability of the first two cervical vertebrae) causes a risk for intubation during surgery.
- Underdevelopment of the femoral head and the acetabulum (hip dysplasia) also occur.
- Celiac disease, gluten sensitivity in the gut causing disturbances may occur in the absorption of certain nutrients, frequently occurs in patients suffering from the syndrome.
- Also is common for constipation.
- Osteoporosis is with Down syndrome more often and at a younger age.
- At a later age (over 50, 60 years), we see mostly dementia arise, often of the Alzheimer's type. This form of dementia presents in patients with Down syndrome very specific abnormalities on the EEG (brain) and is undetectable.
- Epilepsy may also arise, often in old age in people who also suffer from Alzheimer's disease. People with Down syndrome are more susceptible to the effects and side effects of antiepileptic drugs.
Down syndrome diagnosis
After the birth, the diagnosis of Down syndrome usually not difficult to set up, because of the various typical physical characteristics. Yet it is also still for that after birth not immediately stands out. In Western countries, the diagnosis is often made even before birth. Using ultrasound one can differentiate between the 11th and 14th week of pregnancy to measure the nuchal translucency, and this one is at a fetus with Down often thickened. One combines this measurement with the determination of a number of substances in the blood of the mother (PAPP-A and beta-HCG), then the chance of a child with Down syndrome with an accuracy of 90% are predicted. Echoscopische this one also combines with a measurement of the nasal bone, then the reliability even 95%. In the event of a risk is typically greater than 1: 250 recommended an amniocentesis, which can be diagnosed. An amniocentesis, however, is not without risk; the chance of the loss of the pregnancy by the surgery was in studies from the 1970s estimated at 0.5%. Recent research shows the attributive risk to be 0.06%.
There may be several reasons why parents want to know if they risk to get a child with Down syndrome:
- To prepare for the extra care that a child with Down Syndrome often need.
- To proceed with induced abortion on their fetus.
- In the medical field there can be anticipated on the delivery. The woman can carry out research into possible prenatal heart defects and if necessary the birth in a hospital with a specialized neonatal Department.
Imaging
Because some people with Down syndrome do well (eg following a backpack just education), the image that many people have the syndrome since the nineties has become a lot more positive.