What Is Down Syndrome?

Overview

Down syndrome is a genetic condition resulting from the gain of an extra chromosome during fetal development. Chromosomes are the genetic material in our body responsible for all of a person’s inherited traits. Typically, a baby is born with 23 pairs of chromosomes: 23 single chromosomes from the father and 23 chromosomes from the mother. Signs of the disorder are usually present at birth.¹

Causes of down syndrome

Down syndrome is due to abnormal cell division, which results in having a full or partial extra chromosome 21.^1,2 Genetic mutations can cause Down syndrome in one of three ways: 

• Trisomy 21: 95% of Down syndrome cases are caused by trisomy 21.¹ The individual has three copies of chromosome 21 instead of the usual two copies. This is caused by abnormal cell division during sperm cell or egg cell development.
• Mosaic Down syndrome: This is a rare condition where the person has only some cells with an extra chromosome 21, while other cells have the usual pair. This is a result of abnormal cell division after fertilization.
• Translocation Down syndrome: Occurs in only about 3–4% of children with Down syndrome.¹ Chromosome 21 is translocated or attached to another chromosome before or during conception. The individual, therefore, has the usual two copies of chromosome 21 in addition to the portion of chromosome 21 that is attached to another chromosome. 

There are currently no known behavioural or environmental factors behind these genetic changes. 

Signs and symptoms of down syndrome

Down syndrome is characterized by commonly shared physical and mental features; however, these features may vary from person to person and even vary at different times of their lives. Each person with Down syndrome is unique, possessing these characteristics to different degrees.³

The physical development of children with Down syndrome is slower than that of children without it. Physical symptoms of Down syndrome include:^1,2 

• Face and nose bridge flattening
• Small head
• Short neck and shorter height
• Small ears
• Almond-shaped eyes
• An upward slanting of the eyes 
• Brushfield’s spots, which are tiny white spots on the coloured part of the eye 
• Hands that are short and broad with a single palm crease
• Relatively short fingers 
• Decreased and low muscle tones
• Large or protruded tongue. The tongue may stick out of the mouth. 

Intellectual and mental problems associated with thinking and learning may also occur. Despite the presence of these physical and mental differences, children with Down syndrome can develop the communication skills needed to associate with their typically developed peers, though it can take them more time to adjust.^2,4 Common intellectual and behavioural symptoms include:

• Various levels of cognitive impairment
• Short attention span
• Learning disabilities
• Delayed language and speech development
• Poor judgment
• Impulsive behaviour
• Hyperactivity

In addition to intellectual and physical problems, children with Down syndrome are at risk of having health complications^1,3 such as:

• Hearing problems due to repeated ear infections.
• Eye problems, including cataracts.
• Endocrine problems such as hypothyroidism (underactive thyroid).
• Hip problems and risk of dislocation. 
• Congenital heart defects.
• Gastrointestinal defects due to abnormalities in the intestines, oesophagus, trachea, and anus. A person with Down syndrome may suffer from digestive problems such as heartburn, celiac disease, and constipation.
• An increased risk of immune disorders due to abnormalities with the functional immune system. 
• Obstructive sleep apnoea and difficulty breathing at night, resulting from the narrowing of the mouth and airway. 
• Delay in tooth eruption and improper arrangement of the teeth. A greater risk of earlier-onset Alzheimer’s Disease. 

Management and treatment for down syndrome

Down syndrome is managed with supportive care to help children develop physically and mentally to their fullest potential. Treatment includes: 

• Physical therapy
• Speech therapy
• Joining special education programs
• Treating medical conditions related to Down syndrome
• Managing vision problems by wearing glasses
• Using assistive hearing devices for hearing loss

FAQs

How is sown syndrome diagnosed?

Prenatal screening tests and diagnostic tests are two types of tests to detect Down syndrome during pregnancy:

• Screening tests, such as MS-AFP, triple screen and quad-screen, are a combination of serum tests measuring biological markers of Down syndrome in the mother's blood¹. During ultrasound, if there is extra fluid behind the baby's neck, there is a risk for genetic problems. Extra fluid behind the baby’s neck during ultrasound indicates a risk of genetic problems such as Down syndrome. 

Screening tests are safe for both mother and baby; they are not definite but indicate whether the risk of Down syndrome is high or low. 

• Diagnostic tests are performed after positive screening tests; they indicate a definite diagnosis of whether the baby will have Down syndrome or not, but they are more risky for the mother and the developing baby. These tests look for chromosomal changes that cause Down syndrome. 

Types of diagnostic tests include:

• Chorionic villus sampling (CVS) examines material from the placenta (the organ within the uterus during pregnancy providing the foetus with nutrients)
• Amniocentesis involves examining the amniotic fluid, which is the fluid in the sac surrounding the baby, for biological markers of Down syndrome. 
• Percutaneous umbilical blood sampling (PUBS) examines blood from the umbilical cord. 

How can I prevent down syndrome?

There is no way to prevent Down syndrome, as it is a genetic condition. A genetic counsellor will help you know the risk of having a child with a genetic condition such as Down syndrome. 

What are the risk factors for down syndrome?

Although the exact cause of Down syndrome is unknown, and most of the time, the extra chromosome happens by chance, some parents have a higher chance of having a baby with Down syndrome. Risk factors associated with an increasing risk of having a child with Down syndrome include: 

• Advancing maternal and paternal age- Down syndrome risk increases above the age of 35, as reproductive cells (eggs and sperm) are more prone to improper division.^2,3
• Genetics- Parents who themselves have chromosomal disorders, such as being carriers of the genetic translocation of Down syndrome are at higher risk of having children with Down syndrome.^6,7 
• Family history- Having one child with Down syndrome or another chromosomal disorder increases the chance of having another child with it.^6,7

How common is down syndrome?

Down syndrome is the most common chromosomal disorder. Each year, 6,000 babies are born with Down syndrome.¹ In the UK, 47,000 people have Down syndrome, with 1 in every 1000 babies being born with the condition.⁸

When should I see a doctor?

If the child is diagnosed with Down syndrome, a team of specialists may provide the appropriate medical care to help develop the child's social and physical abilities.²

Summary

Down syndrome is a chromosomal disorder that affects the physical and mental development of children. The exact genetic cause is unknown, but treatment is directed at managing symptoms and engaging the children in the development of social and physical skills. With appropriate care, children with Down syndrome may enjoy a long life expectancy and thrive with their peers.