What is Down’s syndrome?

Karolina Baker, Alphabiolabs

By Karolina Baker, Health Testing Specialist at AlphaBiolabs
Last reviewed: 07/07/2023

Table of contents
  • What is Down’s syndrome?
  • How common is Down’s syndrome?
  • What causes Down’s syndrome?
  • What are the different types of Down’s syndrome?
  • Is Down’s syndrome hereditary?
  • What can impact the probability of having a child with Down’s syndrome?
  • What are the characteristics/features of Down’s syndrome?
  • What are the physical characteristics of Down’s syndrome?
  • What are the developmental and behavioural characteristics of Down’s syndrome?
  • What are the medical complications associated with Down’s syndrome?
  • Are babies tested for Down’s syndrome at birth?
  • What is the treatment for Down’s syndrome?
  • How can I get Down’s syndrome screening during pregnancy?
  • What is NIPT?
  • What are the benefits of an AlphaBiolabs NIPT test?

What is Down’s syndrome?

Down’s syndrome is often characterised as having a full or partial extra copy of chromosome 21 and is sometimes referred to as Trisomy 21. It is one of the most common chromosomal conditions at birth.

In Trisomy 21 pregnancies, there is an increased risk for miscarriage or stillbirth.

The presentations of Down’s syndrome can vary drastically. Individuals with Down’s syndrome have mild to moderate intellectual disability, characteristic facial features, and may have treatable medical conditions, such as congenital heart defects, low muscle tone, and low thyroid levels.

Many individuals with Down’s syndrome lead healthy and active lives. As our understanding of Down’s syndrome continues to grow, the clinical and social management of the condition improves – allowing many individuals to have jobs, relationships and even live independently.

How common is Down’s syndrome?

Down’s syndrome is the most common chromosomal condition and affects approximately 1 in 1,000 births worldwide. This means that in the UK, around 700 babies are born with Down’s syndrome each year.

Source:  National Center on Birth Defects and Developmental DisabilitiesCenters for Disease Control and Prevention

What causes Down’s syndrome?

Down’s syndrome is caused by having an extra critical portion of chromosome 21. This imbalance of chromosomes can be present in all or some cells that make up the body. Passing on an extra copy of chromosome 21 occurs by chance, and even though we know that the likelihood of having a baby with Down’s syndrome increases with age, anyone can have a baby with Down’s syndrome. In most cases, Down’s syndrome is not hereditary and does not run in families.

What are the different types of Down’s syndrome?

There are three different types of Down’s syndrome. People living with all three types of Down’s syndrome show similar presentations in terms of intellectual disability and physical features. Around 95% of Down’s syndrome cases are caused by Trisomy 21 (having an extra full copy of chromosome 21 in all cells). The remaining 5% of cases are caused by one of two rare genetic occurrences.

Trisomy 21

Trisomy 21 is the most common form of Down’s syndrome and occurs when a person has a full, separate, extra copy of Chromosome 21. It accounts for 95% of people with Down’s syndrome.

Mosaicism

In around 2% of people with Down’s syndrome, individuals will have an extra copy of chromosome 21 in some, but not all of the cells in their body. This is known as mosaic Down’s syndrome.

Translocation

The remaining 3% of Down’s syndrome cases are caused by having an extra critical part of, or an extra whole copy of Chromosome 21 that has become attached to another chromosome, rather than existing as its own extra chromosome.

Is Down’s syndrome hereditary?

Down’s syndrome does not usually run in families and is therefore not hereditary. Only 1% of cases of Down’s syndrome have a hereditary component, meaning that it has been passed on from a parent to a child through genes.

What can impact the probability of having a child with Down’s syndrome?

The risk of having a child with Down’s syndrome increases with maternal age. This means that older women have an increased chance of having a pregnancy that is affected by Down’s syndrome.

For example, a 35-year-old woman has a 1 in 350 risk of having a pregnancy affected by Down’s syndrome, and this risk increases year-on-year, whereby the risk by age 45 increases to around 1 in 30.

Paternal age is also known to influence the incidence of Down’s syndrome, but only in pregnant women aged 35 and over.

Maternal Age Incidence of Down’s syndrome
20 1 in 2,000
21 1 in 1,700
22 1 in 1,500
23 1 in 1,400
24 1 in 1,300
25 1 in 1,200
26 1 in 1,100
27 1 in 1,050
28 1 in 1,000
29 1 in 950
30 1 in 900
31 1 in 800
32 1 in 720
33 1 in 600
34 1 in 450
35 1 in 350
36 1 in 300
37 1 in 250
38 1 in 200
39 1 in 150
40 1 in 100
41 1 in 80
42 1 in 70
43 1 in 50
44 1 in 40
45 1 in 30
46 1 in 25
47 1 in 20
48 1 in 15
49 1 in 10

What are the characteristics/features of Down’s syndrome?

The severity of Down’s syndrome can vary drastically, but all people with Down’s syndrome have some degree of learning disability.

There are also several medical conditions that are more common in people with Down’s syndrome.  These can include problems with their heart, hearing, vision, bowel, and an increased likelihood of infections.

What are the physical characteristics of Down’s syndrome?

The physical features of Down syndrome include:

  • Shorter than average height
  • Shorter than average neck
  • Flattened facial features
  • Eyes that slant upward
  • Small ears, hands and feet
  • A tongue that tends to stick out of the mouth
  • Palmar Crease – a line across the palm of the hand
  • Low muscle tone (hypotonia) or loose joints

What are the developmental and behavioural characteristics of Down’s syndrome?

Developmental and behavioural features of Down’s syndrome include:

  • Slower than average to meet developmental milestones such as talking and walking
  • Mild to moderate intellectual disability
  • Problems with verbal memory
  • Expressive communication
  • Short attention span
  • Children with Down’s syndrome tend to me more impulsive and stubborn
  • Children with Down’s syndrome tend to have strong social skills

What are the medical complications associated with Down’s syndrome?

There are several medical conditions that are more common in people with Down’s syndrome.

Medical complications of Down’s syndrome can include:

  • Around 50% of children born with Down’s syndrome are affected by a heart condition
  • More than 50% of children born with Down’s syndrome have vision problems
  • Up to 75% of children with Down’s syndrome have some degree of hearing loss
  • Children born with Down’s syndrome are more susceptible to autism
  • Adults with Down’s syndrome may develop dementia at a younger age

Are babies tested for Down’s syndrome at birth?

After birth, babies will undergo a physical examination, which will identify any common physical characteristics of Down’s Syndrome. If Down’s Syndrome is suspected, a sample of the baby’s blood will be sent for laboratory testing to confirm a diagnosis.

What is the treatment for Down’s syndrome?

The severity and presentation of Down’s syndrome varies drastically between individuals with Down’s Syndrome. Therefore, there is no single standard treatment for Down’s Syndrome. Treatments are based on each individual’s medical, developmental and intellectual needs.

How can I get Down’s syndrome screening during pregnancy?

A screening test for Down’s syndrome, Edward’s syndrome and Patau’s syndrome is available at 10-14 weeks of pregnancy.

The screening test that is most widely available is known as a ‘combined’ test. The combined test comprises of a blood test and an ultrasound scan. The blood test looks at markers found in the blood that can indicate an increased chance of carrying a baby with a chromosomal disorder. The ultrasound scan is used to determine something known as the ‘nuchal translucency’. The results of both of these tests are used along with the age of the pregnant woman to determine the risk of carrying a foetus with Down’s syndrome, Edward’s syndrome or Patau’s syndrome.

In the case of a high-risk result from the combined test, the pregnant woman will be offered the chance to receive NIPT, which is another screening test, or diagnostic testing, which may be an amniocentesis or chorionic villus sampling (CVS). Amniocentesis and CVS will provide a definite answer as to whether or not the baby has Down’s syndrome, Patau’s syndrome or Edward’s syndrome, but in rare cases amniocentesis and CVS can cause a miscarriage. Therefore, many pregnant people are choosing to take a NIPT screening test privately, as it is available to all expectant mothers, irrespective of whether they were classified as high risk by the combined test.

To perform NIPT and CVS/amniocentesis, foetal DNA must be obtained for analysis. Foetal DNA is traditionally acquired through invasive sampling methods e.g. amniocentesis, or CVS. Amniocentesis involves a long, thin needle that is inserted through the abdomen (stomach) to obtain a sample for testing. For CVS, a needle is inserted into the womb to obtain a sample of cells. Both procedures are invasive and increase the risk of pregnancy loss. The increased risk of miscarriage is often a dilemma, and many pregnant women opt for NIPT as their initial screening test.

What is NIPT?

AlphaBiolabs NIPT is a screening test used to determine the risk of a pregnancy being affected by Down’s syndrome, Edward’s syndrome and Patau’s from as early as 10 weeks. This test only requires a sample of the mother’s blood, meaning that there is no risk to either mother or baby.

The AlphaBiolabs test is used to find out if a pregnant woman is carrying a foetus with an increased chance of being affected by a chromosomal condition, known as an aneuploidy. An aneuploidy is a condition caused by having an incorrect number of chromosomes i.e. an extra or a missing copy of a chromosome. This test is a simple blood test with no increased risk to mother or baby.

The three most common chromosomal conditions covered by the Standard AlphaBiolabs test are:

  1. Down’s syndrome (Trisomy 21)
  2. Edwards’ syndrome (Trisomy 18)
  3. Patau’s syndrome (Trisomy 13)

Down’s syndrome is by far the most common chromosomal aneuploidy included in this screening test. As well as Down’s syndrome, the standard AlphaBiolabs NIPT test also screens for Edward’s syndrome, and Patau’s syndrome, which are much more serious than Down’s syndrome, and babies born with these conditions rarely survive past infancy.

Additionally, the Advanced AlphaBiolabs NIPT test can also detect all other aneuploidies, including Autosomal Aneuploidies (AAs) and Sex Chromosome Aneuploidies (SCAs) such as Turner’s syndrome, Klinefelter’s syndrome, Jacob’s syndrome and Trisomy X.

What are the benefits of an AlphaBiolabs NIPT test?

The AlphaBiolabs NIPT test only requires a blood sample, which can be provided by any expectant mother in the first trimester, from 10+ weeks gestation (not just those who received a high-risk result from the combined test). The AlphaBiolabs NIPT test is a laboratory test which detects 97.2%-100% of trisomies in singleton and twin pregnancies.

The AlphaBiolabs NIPT test can also provide foetal sex determination, which is not offered by the NHS.

With results available in in 5-7 working days, you can get results much faster than the traditional testing pathway.

Traditional screening consists of multiple tests across the first and second trimesters, which can detect around 85% of babies with Down’s syndrome, and 80% of babies with Edwards’ syndrome or Patau’s syndrome.

Traditional Screening Tests AlphaBiolabs NIPT
Multiple procedures over the course of the first and/or second trimester One laboratory test at any time over 10 weeks gestation
Combined screening identifies around 85% of babies with Down’s syndrome and 80% of babies with Edwards’ or Patau’s syndrome The AlphaBiolabs NIPT test detects >99.9% of babies with Down’s syndrome, Edward’s syndrome and Patau’s syndrome
Reduced performance of screening in twin pregnancies Equivalent performance of screening in both twin and singleton pregnancies
Results are provided following several tests, which can take some time Results provided within 5-7 working days
Can involve invasive methods that can harm the mother and baby and carry an increased chance of miscarriage Blood test taken from mother’s arm, posing no risk to mother or baby
No gender identification Gender identification available
Tests for Down’s syndrome, Edward’s syndrome and Patau’s syndrome only Can look for chromosomal changes in all 46 chromosomes
NIPT if offered only to pregnancies determined as ‘high-risk’ by the combined test Can be taken by any pregnant person, irrespective of the risk status determined by the combined test

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Karolina Baker

Karolina Baker

Health Testing Specialist at AlphaBiolabs

Karolina joined AlphaBiolabs in 2021, and holds the role of Health Testing Specialist.

As well as overseeing a range of health tests, Karolina plays an active role in the research and development of the company’s latest health test offerings.

Before joining AlphaBiolabs, Karolina worked as an Associate Practitioner at Mid-Cheshire Hospitals NHS Foundation Trust, and as a research assistant at the Turner Laboratory, within the Faculty of Biology, Medicine and Health at The University of Manchester.

Karolina’s main scientific interests include clinical genomics and genetic diagnostics. Her qualifications include a BSc in Molecular Biology and an MSc in Genomic Medicine.

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