It is a genetic condition that occurs when there is an extra copy of a specific chromosome: chromosome 21.
Most babies are born with 46 chromosomes in every cell, 23 from the mother and 23 from the father. Babies with Down syndrome have an extra copy of chromosome 21, which causes distinct physical, intellectual, and developmental symptoms.
People who have Down syndrome usually have cognitive development profiles that suggest mild to moderate intellectual disability. However, cognitive development and intellectual ability are highly variable.
They also have an increased risk for certain medical conditions such as congenital heart defects, obesity, respiratory and hearing problems, Alzheimer’s disease, gastrointestinal disorders, childhood leukemia, and thyroid conditions.
As the World marks, Down Syndrome Day here is everything you should know about the causes, types, diagnosis and treatment of the condition.
Causes and Risk factors
Although its exact cause is also unknown, Women from 35 and above have a higher chance of having a child with Down syndrome.
If you’ve already had a child with Down syndrome, you’re more likely to have another one who has it as well.
It’s not common, but it is possible to pass Down syndrome from parent to child. Sometimes, a parent has what experts call “translocated” genes. That means some of their genes aren’t in their normal place, perhaps on a different chromosome from where they’d usually be found.
The parent doesn’t have Down syndrome because they have the right number of genes, but their child may have what’s called “translocation Down syndrome.”
- Trisomy 21. This is by far the most common type, where every cell in the body has three copies of chromosome 21 instead of two.
- Translocation Down syndrome. This accounts for only 3% to 4% of all cases. In this type, each cell has part of an extra chromosome 21 or an entirely extra one but it’s attached to another chromosome instead of being on its own.
- Mosaic Down syndrome. This is the rarest type, where only some cells have an extra chromosome 21.
Down Syndrome can be diagnosed before birth as women with a higher chance of having a child with Down syndrome might receive screening and diagnostic tests.
Women aged 30–35 years or above might receive genetic screening during pregnancy. This is because the chance of having a child with Down syndrome increases as women age.
Screening tests include:
- Nuchal translucency testing: At 11–14 weeks, an ultrasound can measure the clear space in folds of tissue behind the neck of a developing fetus.
- Triple screen or quadruple screen: At 15–18 weeks, this measures the quantities of various substances in the mother’s blood.
- Integrated screen: This combines results from first-trimester blood and screening tests, with or without nuchal translucency, with second-trimester quadruple screening results.
- Cell-free DNA: This is a blood test that analyzes fetal DNA present in the mother’s blood.
- Genetic ultrasound: At 18–20 weeks, doctors combine a detailed ultrasound with blood test results.
Screening is a cost-effective and less invasive way to determine whether more invasive diagnostic tests are needed.
However, unlike diagnostic tests, they cannot confirm whether Down syndrome is present.
Diagnostic tests are more accurate for detecting Down syndrome. A healthcare 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 8–12 weeks, a doctor might obtain a tiny sample of placenta for analysis, using a needle inserted into the cervix or the abdomen.
- Amniocentesis: At 15–20 weeks, they may obtain a small amount of amniotic fluid for analysis, using 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 analysis, using a needle inserted into the abdomen.
A healthcare professional can also diagnose Down syndrome after a baby is born by inspecting their physical characteristics, blood, and tissue.
Down syndrome is a lifelong condition that can’t be treated. But your child can live a fulfilling life with proper assistance, whether it’s in the form of specialty doctors, early intervention services, occupational therapy, speech therapy, physical therapy, or special needs classes.