Trisomy

Trisomy

Trisomy refers to a chromosomal condition characterized by the presence of an extra chromosome in the cells of an organism, resulting in a total of three copies of a particular chromosome instead of the normal two. This genetic anomaly can lead to various developmental and health issues, depending on which chromosome is affected. Trisomy conditions are a type of aneuploidy, a term that refers to an abnormal number of chromosomes.

Karyotype showing Trisomy 21, also known as Down Syndrome.

Causes

Trisomy is most often caused by nondisjunction, an error in cell division where chromosomes fail to separate properly. This error can occur during meiosis, the process of forming egg or sperm cells, leading to reproductive cells with an abnormal number of chromosomes.

Common Types of Trisomy

• Trisomy 21 (Down Syndrome): The most well-known trisomy, characterized by an extra copy of chromosome 21. It is associated with intellectual disability, distinct facial features, and a higher risk of certain medical conditions.
• Trisomy 18 (Edwards Syndrome): Marked by severe developmental delays and physical abnormalities. Many affected pregnancies result in miscarriage or stillbirth.
• Trisomy 13 (Patau Syndrome): Associated with severe intellectual disability and physical malformations. Many affected individuals do not survive beyond infancy.

Symptoms and Effects

Symptoms can vary widely depending on the specific trisomy but may include:

• Developmental delays and intellectual disability
• Physical abnormalities such as heart defects, kidney problems, and distinct facial features
• Growth retardation
• Increased risk of certain health conditions

Diagnosis

Diagnosis of trisomy conditions can occur before birth through prenatal screening and diagnostic tests such as:

• Ultrasound scans: Can detect physical abnormalities associated with trisomies.
• Blood tests: Measure markers that may indicate a trisomy.
• Amniocentesis or chorionic villus sampling (CVS): Invasive tests that analyze the chromosomes in fetal cells.

After birth, diagnosis can be confirmed through a karyotype analysis, which examines the number and appearance of an individual’s chromosomes.

Treatment and Management

There is no cure for trisomy conditions, but early intervention and supportive therapies can improve outcomes. Management may include:

• Specialized educational programs
• Physical, occupational, and speech therapies
• Regular health screenings and medical care to manage associated conditions

See Also

• Genetic disorder
• Chromosome
• Prenatal testing
• Special education

References

• National Human Genome Research Institute. "Facts About Trisomy Conditions."
• March of Dimes. "Chromosomal Conditions."

External Links

• Genetics Home Reference: Down Syndrome
• March of Dimes: Chromosomal Conditions

Trisomy Resources
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