What is Down’s syndrome?

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.

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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 Disabilities, Centers 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 traditional screening test for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome is available at 11-13 weeks of pregnancy. Known as a ‘combined’ test, it comprises 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, while the ultrasound scan is used to determine something known as the ‘nuchal translucency’.

The results of both these tests, along with the age of the pregnant woman, determine the risk of carrying a foetus with Down’s, Edwards’ or Patau’s syndrome.

In the case of a high-risk result, the pregnant woman will be offered the chance to receive non-invasive prenatal genetic testing (NIPT), another screening test, or diagnostic testing.

Diagnostic testing typically involves amniocentesis or chorionic villus sampling (CVS). For amniocentesis, a long, thin needle is inserted into the abdomen to obtain a sample of amniotic fluid for testing. For CVS, a needle is inserted into the womb to obtain a sample of cells from the placenta.

These tests will provide a definite answer as to whether or not the baby has Down’s, Edwards’ or Patau’s syndrome. However, both tests are invasive and carry a small risk of miscarriage.

For this reason, many pregnant women are choosing private NIPT screening, as it is non-invasive, and available to all expectant mothers irrespective of whether they were classified as high risk by the combined test.

For an AlphaBiolabs NIPT, all that’s required is a blood sample, which is collected from the mother’s arm. This makes the test 100% safe for mum and baby, with no risk of miscarriage.

The test uses next-generation sequencing to analyse cell-free foetal DNA (cffDNA) – fragments of the baby’s DNA that naturally circulate in mum’s bloodstream during pregnancy – and detect chromosomal abnormalities, including Down’s syndrome.

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What is NIPT?

AlphaBiolabs NIPT is a test used to screen unborn babies for certain genetic conditions, including Down’s syndrome, Edwards’ syndrome and Patau’s syndrome, from as early as 10 weeks into pregnancy.

This test only requires a sample of the mother’s blood, making it completely non-invasive and 100% safe for mum and baby.

The test can determine if there is an increased chance of an unborn baby 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.

The three most common chromosomal conditions covered by the Standard AlphaBiolabs NIPT are Down’s (Trisomy 21), Edwards’ (Trisomy 18) and Patau’s syndrome (Trisomy 13).

Down’s syndrome is by far the most common chromosomal aneuploidy included in the screening test.

We also offer:

• Advanced NIPT – screens for the three trisomies covered by our Standard test, plus all other autosomal aneuploidies (Aas) and sex chromosome aneuploidies (SCAs), caused by having an abnormal number of sex chromosomes (X and Y chromosomes).
• Premium NIPT – includes everything covered in our Advanced test plus six specific microdeletions, a group of conditions caused by the absence of a small portion of specific chromosomes. The inclusion of microdeletions makes this the most comprehensive screening test offered at AlphaBiolabs.

Call 0333 600 1300 to order your NIPT test

What are the benefits of an AlphaBiolabs NIPT test?

NIPT has shown much higher accuracies compared to traditional screening methods, which include many different tests over the course of the first and second trimester.

Traditional screening offered by the NHS during pregnancy is known as the ‘combined test’ and is typically carried out at 11-13 weeks. It consists of an ultrasound scan to measure the nuchal translucency (NT) and a blood test to look at protein markers.

Together, these factors are used to predict the probability of the foetus having Down’s, Edward’s and Patau’s syndrome. In the case of a high-risk result, the pregnant woman will be offered the chance to receive non-invasive prenatal genetic testing (NIPT), another screening test, or diagnostic testing (amniocentesis or chorionic villus sampling/CVS).

For amniocentesis and CVS, foetal DNA is obtained through invasive sampling methods.

Amniocentesis requires a long, thin needle to be 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 miscarriage.

In contrast, an AlphaBiolabs NIPT is 100% safe for mum and baby, and completely non-invasive, with only a blood sample from mum required.

With this single blood test, performed from as soon as 10 weeks into pregnancy, the AlphaBiolabs NIPT can detect chromosomal conditions in an unborn baby with an accuracy of over 99.99%.

Results are available in just 6 business days – much quicker than NHS screening.

The test also includes optional, free foetal sex determination.

How AlphaBiolabs NIPT compares to traditional screening tests:

	Traditional screening tests	AlphaBiolabs NIPT
Number of tests	Multiple procedures over the course of the first and/or second trimester	One blood test that can be taken from as early as 10 weeks gestation
What does it screen for?	Combined screening identifies around 85% of babies with Down’s syndrome and 80% of babies with Edwards’ or Patau’s syndrome	Over 99.99% accurate for detecting chromosomal abnormalities
Screening in twin pregnancies	Reduced performance of screening in twin pregnancies	Equivalent performance of screening in both twin and singleton pregnancies
Speed of results	Results are provided following several tests, which can take some time	Results provided within 6 business days
Sample collection	Can involve invasive methods, carrying an increased chance of miscarriage	Blood sample taken from mother’s arm – non-invasive and 100% safe for mum and baby
Can you find out the baby’s sex?	No early gender identification	Optional foetal sex determination, at no extra cost