Trisomy is a genetic disorder in which a child is born with all or part of an extra chromosome. Normally, humans have two copies of all chromosomes (except males, who have a different pair of chromosomes in the form of the X and Y sex chromosomes). In Trisomy, one is born with a third copy or a third copy of the chromosome. This happens during the development of sex cells (egg and sperm). When sex cells go through cell division (which is one stage of sex cell development) the chromosomes don’t separate as they should. This is called non-disjunction, and it is because the egg or sperm cell has extra chromosomes when it is formed. The egg or sperm cell carries these extra chromosomes for the fertilization event. That will mean revealing the child will have this extra chromosome or trisomy.
Trisomy is not well tolerated by humans and in many cases developing a child before being carried is delivered to full term. However, there are few cases of Trisomy in which the baby can be carried to full term and born, but the child usually has some type of disorder due to the presence of extra chromosomes. These include Trisomy 18, Trisomy 21 and Trisomy sex chromosomes.
In Trisomy 18 or Edwards Syndrome, the child has an extra copy of the full or partial chromosome 18. The survival rate for Trisomy 18 is not good A child born with Trisomy 18 can have a variety of life-threatening defects, including heart defects; kidney problems; delayed progress; problems with the digestive system (intestine born outside the body, and not connecting the esophagus with the stomach); of humor in the brain; and umbilical or inguinal hernia. These defects are so serious that less than 10% of children born with Trisomy 18 will ever celebrate their 1st birthday. However, some children with Trisomy 18 can live well into their 20s and 30s, but they usually need constant care and cannot live independent life
In Trisomy 21 or Down syndrome, the child has an extra copy of chromosome 21. Survival for Trisomy 21 is much better than for Trisomy 18. Many children with Trisomy 21 survive well into their 50s and 60s. A child born with Trisomy 21 may have a variety of developmental problems that vary from mild to severe. These defects can include birth defects heart, eye problems, hip problems (to move leading), sleep apnea, and hypothyroidism. In addition, mental and social development may be delayed, which can lead to slow learning, short attention spans, poor judgment, and impulsive behavior. They may also have short body features (due to arrested development), excessive skin around the neck, flattened nose, small ears and mouth . Their head may be smaller than normal and have an abnormal shape. Many people with Trisomy 21 need constant care for the rest of their lives, but some can live close to normal lives in group homes . which have special support for people with Trisomy 21.
Other types of trisomy include trisomy of the sex chromosomes including XXY and XYY in males and 30 in females. These normally do not have the same developmental effects as trisomy 18 and 21. Trisomy sex chromosomes can cause an individual to be infertile and cause some external physical effects as the development of the chest in the seas with XXY. However, individuals with sex chromosome trisomy often approach normal intelligence and live a normal life without constant life lead to care for trisomy 18 and 21 individuals.
There are no treatments for trisomy in humans. Only the symptoms of the disorder can be treated. The diagnosis of these disorders is made by testing the cells to see if the cell carries extra chromosomes. This can be done after delivery or during an amniocentesis pregnancy test if your doctor feels you are at risk for having a child with trisomy disorder. The incidence of a woman giving birth to a trisomy child increases with age.
References
http://www.trisomy18.org/site/PageServer?pagename=whatisT18_quid
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001992/
