Down Syndrome: Causes, Symptoms, Types & Tests

Down syndrome is a genetic disorder resulting from extra genetic material on chromosome 21. This additional genetic information affects a baby's physical and brain development. Individuals with Down syndrome have some physical traits, developmental differences, and a higher risk of developing some health issues.

A healthy and fulfilled life for a person with Down syndrome is possible with proper medical care, therapy, education, and support from families. Knowledge of the causes, symptoms, types, screening, diagnostic tests, and lifelong management for Down syndrome assists parents and families in making informed decisions.

What Is Down Syndrome?

Down syndrome is a chromosomal disorder that involves having an extra copy of chromosome 21. Usually, an individual carries 46 chromosomes arranged in 23 pairs. In Down syndrome, there is duplicate 21st chromosome material. The condition impacts learning, communication, development, and physical development. But what it does do is vary widely between individual people. There are some developmental differences that are benign, while others are more significant and require more support.

Down Syndrome Causes

Excessive amounts of material on chromosome 21 are responsible for most cases of Down syndrome. Most often, this occurs as a consequence of division errors in the process of making reproductive cells or in early development. There are three types of Down syndrome: The most prevalent form is trisomy 21, where there are three copies of chromosome 21 in each cell. There is another form, called translocation Down syndrome, in which there is part of the extra 21 material that connects to another chromosome.

A genetic counselling service is important for families with a history of translocation Down syndrome, as a parent may carry a balanced translocation that can increase the chance of having a child with translocation Down syndrome. The third form is mosaic Down syndrome, involving some cells with an extra chromosome 21 and others with the normal two. The risk of having a child with Down syndrome rises with age (especially over age 35) for the mother. Females also tend to be younger, so there are just additional pregnancies in younger age groups than in older ones, so babies with Down syndrome are also born to younger mothers.

Down Syndrome Symptoms

Individuals experience different symptoms of Down syndrome. These physical characteristics tend to develop naturally during childhood and show up. There are many physical similarities such as a relatively flat facial convexity, upward-slanting eyes, shorter hands and feet, a single crease across the palm, smaller ears, and lower muscle tone. But developmental differences also occur. Children with Down syndrome develop some skills at a later age than other children. For instance, baby steps in speech and language acquisition are delayed.

Some medical conditions are associated with Down syndrome. Some of these are congenital heart defects, hearing and vision issues, and obstructive sleep apnea. Conditions are identified and managed if they occur through good medical follow-up, which is provided regularly. The presence of one or more of the following does not mean Down syndrome. Genetic testing is recommended to confirm the diagnosis by a health care provider.

Down Syndrome Types

There are three main Down syndrome types:

Trisomy 21

About 95% of Down syndrome is caused by trisomy 21. In this form, each cell has three copies of chromosome 21 instead of two.

Translocation Down Syndrome

Translocation Down syndrome is a syndrome in which all, or some, of the material of chromosome 21 is fused onto another chromosome. This type only makes up around 3% of cases. The specific pattern of chromosomes can be determined by genetic testing.

Mosaic Down Syndrome

In mosaic Down syndrome, there are cells with both two and three copies of chromosome 21. It makes up approximately 2% of the cases. The characteristics and developmental impacts differ depending on the proportion and distribution of cells with the extra chromosome 21. Although these genetic types are different, they have overlapping physical and developmental features.

Down Syndrome Tests During Pregnancy

During pregnancy, there are two major types of Down syndrome tests: screening tests and diagnostic tests. If a screening test is done, it takes an educated guess at estimating the risk that a developing fetus has Down syndrome. They are not diagnostic of the condition. In some cases, first trimester screening includes an ultrasound procedure called a nuchal translucency scan, as well as a blood test of the mother.

Another option for screening is using blood during pregnancy. Cell-free DNA testing or non-invasive prenatal testing can be performed from around 10 weeks of pregnancy. It analyzes placental DNA fragments found in the mother's blood to estimate the likelihood of Down syndrome. When a screening test shows an increased risk, a doctor suggests further tests.

Diagnostic Tests for Down Syndrome

Genetic testing is used to identify Down syndrome even before the baby is born. A sample of cells from the placenta is used for chromosomal analysis in chorionic villus sampling (CVS). It is carried out earlier in the gestation than amniocentesis.

An amniocentesis procedure is used to obtain a small sample of amniotic fluid, which contains fetal cells. The cells are then checked for any abnormalities in chromosomes. CVS and amniocentesis are invasive methods which result in a small amount of risk. For pregnant women, the pros and cons of testing should be discussed with the health care provider before the decision is made.

Diagnosis After Birth

After a baby is born, a doctor may initially suspect Down syndrome based on physical features and developmental findings. However, these features alone cannot confirm the condition. A blood sample can be examined to determine the baby's chromosomes and confirm whether extra chromosome 21 material is present. This genetic testing can also help identify which type of Down syndrome is present.

Down Syndrome Testing at Molecular Diagnostics and Therapy

At Molecular Diagnostics and Therapy, our advanced diagnostic tests help doctors and parents with genetic or chromosomal testing if needed. The decision to do testing must always come with consultation by a licensed healthcare professional. Results of prenatal testing give information about the risk of Down syndrome, while diagnostic testing gives more concrete results when needed. It is essential to know the difference between screening and diagnostic testing when talking about Down syndrome during pregnancy.

Conclusion

Down syndrome is a genetic disorder resulting from extra genetic material on chromosome 21. Symptoms and the way individuals with Down syndrome require accommodations for learning vary, but this disease affects physical development, learning, and overall health of an individual. Learning about causes, symptoms, different types of Down syndrome, and testing done to diagnose Down syndrome is necessary to help identify it and get medical advice when needed.