The estimated incidence of Down syndrome is between 1 in 1,000 to 1 in 1,100 live births. Each year approximately 3,000 to 5,000 children are born with this chromosome disorder. It is believed there are about 250,000 families in the United States who are affected by Down syndrome. The vast majority of children with Down syndrome (approximately 95 percent) have an extra 21 chromosome. Instead of the normal number of 46 chromosomes in eachcell, the individual with Down syndrome has 47 chromosomes.
Trisomy 21 is the most common type of down syndrome and it account for 95% of cases. When someone has trisomy 21 they have 47 chromosomes instead of 46 in every cell, which is caused by an error in cell division known as nondisjunction. Usually a baby inherits genetic information from both parents, 23 from each parent, but at some point during cell division a pair of 21st chromosomes in either the X or Y chromosome fails to separate, causing the child to have an extra 21st chromosome. This one extra chromosome is the cause of down syndrome’s development delays and physical features that are associated with down syndrome. Translocation down syndrome accounts for about 3% of cas... ... middle of paper ... ...hat conceive over the age of 35 and older are most likely to have a child with the condition.
Down Syndrome is also (or formally) known as mongolism, and is the most frequent chromosomal abnormality in the United States. Over 350,000 people carry this condition. It is caused by an extra 21st chromosome. This is also known as trisomy 21. Instead of 46 chromosomes in each cell it was determined that an extra 21st chromosome affected Down syndrome, this occurs 95% of the time.
This disease can develop either before or after a child is born. Less than 1,000 pregnancies for mothers less than 30 years of age result in a baby with Down syndrome. For mothers who are 44 years of age, about 1 in 35 pregnancies results in a baby with Down syndrome (Crosta). The only way to have a child with Down syndrome is determined by the mother’s age. 75-80% of babies that have Down syndrome are born to younger mothers.
About three to four percent of cases are because of translocation which is chromosome 21 detaches and attaches to another chromosome. Mosaicism accounts for only one to two percent of births, which is an abnormal cell division with the normal 46 chromosomes while the others have 47 creating a mosaic of normal and abnormal cells (Encarta.p1). The presence of Down syndrome in children is also due to the age of the mother. A twenty five year old woman' s chance of having a baby with Down syndrome is 1 in 1,250, but a woman who is thirty five it's 1 in 378 and a woman 45 it's1 in 30 (Encarta.p2). Diana Danilenko-Dixon, M.D.
Down syndrome typically occurs as the result of having an extra twenty first chromosome. This extra twenty first chromosome can be seen in the picture to the left. This extra chromosome in the cell happens as a mistake that takes place during cell division between the female’s egg cell and the male’s sperm cell. This error in cell division, known as nondisjunction, is the cause of 95% of Down syndrome births. This is also referred to as Trisomy 21.
But is a sufferer of HD, the repeat count is from 37 to 86. While nobody has found a direct correlation between the number of repeats and the age when symptoms appear, there is evidence that people with very high numbers of repeats contract the rarer early- onset Huntington's disease, which usually affects people under the age of 20. It is estimated that between .1 and 10 % of people who suffer from Huntington's disease have obtained it through new mutations. There are three different tests for Huntington's disease. The first, presymptomatic testing, is for people who are at risk for the disease.
In hereditary CJD, the infected person has inherited an abnormal gene due a family history of the disease or takes a test in which their results are positive for a genetic mutation that is associated with Creutzfeldt-Jakob disease. About 5 to 10 percent of cases of Creutzfeldt - Jakob disease in the United States are hereditary and the United Kingdom has a population in the region of 58 million and there are only a few instances of deaths due to genetic CJD in a year. In acquired CJD, the disease is transmitted by exposure to brain or nervous system tissue, usually through certain medical procedures. Acquired CJD is also very rare; so far there has been no solid evidence that CJD is transmittable through casual encounter with a patient with CJD. Since Creutzfeldt - Jakob disease was first discovered in 1920, less than 1 percent of cases have been diagnosed as acquired CJD.
There are many different ways to classify autism; by difficulties in social interaction, verbal and non-verbal communication and repetitive behavior. Autism appears to have its roots in very early brain development, however most signs of autism become obvious around two and three years old. According to the U.S Centers for Disease and Control and Prevention about 1 and 68 American children are diagnosed with Autism. Studies have showed that autism is four to five times more common in boys than girls. Which is an estimated 1 out of 42 boys are diagnosed with it compared to an estimated 1 out 189 girls are diagnosed with in the United States.
Finally, Translocation Down syndrome results when an “extra part or a whole extra chromosome 21 is present, but it is attached or “trans-located” to a different chromosome rather than being a separate chromosome 21” (“Facts about Down Syndrome”). In this case, only an “unbalanced” translocation, where genetic material is either lost or gained can cause Down syndrome. Down syndrome remains the most prevalent genetic disorder in humans. According to the National Down Syndrome Society, it affects about 1 out of every 691 newborns and more than 400,000 individual... ... middle of paper ... ... at an increased risk for heart defects, vision and hearing problems, blood disorders, and digestive problems. Almost 50% of babies with the disorder have congenital heart disease.