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Down syndrome: Difference between revisions
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[[Image:Trisomy_in_Down_syndrome.jpg|frame|right|[[Trisomy]], the hallmark of Down syndrome, results when a baby is born with three copies of [[chromosome]] 21 instead of the usual two.]] | [[Image:Trisomy_in_Down_syndrome.jpg|frame|right|[[Trisomy]], the hallmark of Down syndrome, results when a baby is born with three copies of [[chromosome]] 21 instead of the usual two.]] | ||
Down syndrome is a disease caused by an irregular number of chromosomes. There are three causes of trisomy 21. [http://www.ds-health.com/trisomy.htm]The most common is called nondisjunction. Nondisjunction happens during cell division. When a cell goes normally through meiosis, the | Down syndrome is a disease caused by an irregular number of chromosomes. There are three causes of trisomy 21. [http://www.ds-health.com/trisomy.htm]The most common is called nondisjunction. Nondisjunction happens during cell division. When a cell goes normally through meiosis, the chromosomes are divided evenly between the two daughter cells, but when no disjunction occurs, the chromosomes are split unevenly, giving one daughter cell extra chromosomes and the other one a less than normal amount. [http://www.wrongdiagnosis.com/n/nondisjunction/intro.htm] If and egg or sperm cell with an uneven number of chromosomes combines with a normal cell, the resulting fetus will have a third twenty-first chromosome, and therefore, will have Down syndrome. | ||
Robertsonian Translocation is the second leading cause of Down syndrome. Robertsonian Translocation is a condition that causes breaks to occur in the chromosomes. These breaks normally occur in the thirteenth through fifteenth and the twenty-first or twenty-second chromosomes. Individuals with this condition have a high risk of giving birth to a child with a chromosomal imbalance. A woman who has Robertsonian Translocation affecting her twenty-first chromosome has a ten to fifteen percent chance that she will give birth to a child with Down syndrome.[http://www.spokane.wsu.edu/research&service/HREC/medical_sciences/RobertsonianTranslocationResource.asp] | Robertsonian Translocation is the second leading cause of Down syndrome. Robertsonian Translocation is a condition that causes breaks to occur in the chromosomes. These breaks normally occur in the thirteenth through fifteenth and the twenty-first or twenty-second chromosomes. Individuals with this condition have a high risk of giving birth to a child with a chromosomal imbalance. A woman who has Robertsonian Translocation affecting her twenty-first chromosome has a ten to fifteen percent chance that she will give birth to a child with Down syndrome.[http://www.spokane.wsu.edu/research&service/HREC/medical_sciences/RobertsonianTranslocationResource.asp] | ||
The third cause of trisomy 21 is mosaicism. Mosaicism is a condition were an individual has cells that do not all have the same genes. Some cells have a normal number of chromosomes while others have an abnormal amount. This condition can affect a person’s sperm and egg cells as well. If a | The third cause of trisomy 21 is mosaicism. Mosaicism is a condition were an individual has cells that do not all have the same genes. Some cells have a normal number of chromosomes while others have an abnormal amount. This condition can affect a person’s sperm and egg cells as well. If a parent's reproductive cells has and abnormal amount of chromosomes, their child could be born with Down syndrome.[http://www.nlm.nih.gov/medlineplus/ency/article/001317.htm] | ||
==Diagnosis== | ==Diagnosis== | ||
