It is a genetic condition that occurs when there is an extra copy of a specific chromosome: chromosome 21.
Down Syndrome: Causes, Types, Diagnosis and Management
Most babies are born with 46 chromosomes in each cell, 23 from the mother and 23 from the father. Babies with Down syndrome have an extra copy of chromosome 21, causing distinctive physical, intellectual, and developmental symptoms.
People with Down syndrome typically have cognitive development profiles that suggest mild to moderate intellectual disability. However, cognitive development and intellectual capacity are highly variable.
They are also at increased risk for certain medical conditions, including congenital heart defects, obesity, respiratory and hearing problems, Alzheimer’s disease, gastrointestinal disorders, childhood leukemia, and thyroid conditions.
As we mark World Down Syndrome Day today, March 21, here’s everything you need to know about the causes, types, diagnosis, and treatment of the condition.
Causes and risk factors
Although its exact cause is also unknown, women over the age of 35 are more likely to have a child with Down syndrome.
If you have already had a child with Down syndrome, it is more likely that you will have another who has it as well.
It is not common, but it is possible to pass Down syndrome from parents to children. Sometimes a parent has what experts call “translocated” genes. That means some of his genes are not in their normal place, perhaps on a different chromosome than where they are normally found.
The father does not have Down syndrome because he has the correct number of genes, but his son may have what is called “translocation Down syndrome.”
Types of Down Syndrome
- Trisomy 21. This is by far the most common type, where each cell in the body has three copies of chromosome 21 instead of two.
- Translocation Down syndrome. This represents only 3% to 4% of all cases. In this type, each cell has part of an extra chromosome 21 or a whole extra chromosome, but it is attached to another chromosome instead of standing alone.
- Mosaic Down syndrome. This is the rarest type, where only a few cells have an extra chromosome 21.
Diagnosis of Down Syndrome
Down syndrome can be diagnosed before birth, as women with a higher chance of having a child with Down syndrome can receive screening and diagnostic tests.
Women ages 30 to 35 and older can undergo genetic testing during pregnancy. This is because the chance of having a child with Down syndrome increases as a woman ages.
Screening tests include:
- Nuchal translucency test: At 11 to 14 weeks, an ultrasound can measure the free space in the folds of tissue behind the neck of a developing fetus.
- Triple Screen or Quad Screen: At 15–18 weeks, it measures the amounts of various substances in the mother’s blood.
- Integrated screen: This combines the results of the first trimester screening and blood tests, with or without nuchal translucency, with the results of the second trimester quad screen.
- cell-free DNA: This is a blood test that analyzes the fetal DNA present in the mother’s blood.
- Genetic Ultrasound: At 18–20 weeks, doctors combine a detailed ultrasound with the results of a blood test.
Screening is a cost-effective and less invasive way to determine if more invasive diagnostic tests are needed.
However, unlike diagnostic tests, they cannot confirm that Down syndrome is present.
Diagnostic tests for Down Syndrome
Diagnostic tests are more accurate in detecting Down syndrome. A health professional will usually perform such tests inside the uterus.
However, they increase the risk of miscarriage, fetal injury, and preterm labor.
Diagnostic tests include:
- Chorionic villus sampling: At 8 to 12 weeks, a doctor can obtain a small sample of the placenta for testing by inserting a needle into the cervix or abdomen.
- Amniocentesis: At 15-20 weeks, they can obtain a small amount of amniotic fluid for analysis through a needle inserted into the abdomen.
- Percutaneous umbilical blood sampling: After 20 weeks, the doctor may take a small sample of blood from the umbilical cord for testing by inserting a needle into the abdomen.
A health professional can also diagnose Down syndrome after a baby is born by inspecting its physical characteristics, blood, and tissue.
Management of Down Syndrome
Down syndrome is a lifelong condition that cannot be treated. But your child can live a full life with the right support, whether it’s in the form of medical specialists, early intervention services, occupational therapy, speech therapy, physical therapy, or special needs classes.
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