What is Down syndrome?

Down syndrome is a genetic disorder caused by abnormal cell division during pregnancy. Human cells contain 23 pairs of chromosomes, and this abnormal cell division results in an extra copy of chromosome 21. Thus, the 21st pair will have three chromosomes rather than two.

Who discovered Down syndrome?

John Langdon Down, an English physician, characterised this syndrome in his scholarly work published in 1866. There were many to do this before him, but Down described this as a distinct entity. This syndrome was then referred to as ‘Down Syndrome.’

During the advances in medicine and science, researchers started investigating more about this condition. And in 1959, Dr. Jerome Lejeune declared Down syndrome as an abnormal chromosomal condition happening during the cell division. 

Likelihood of Down syndrome in Babies

According to recent statistics, the likelihood of Down syndrome is 1 in 850 to 900 babies. Trisomy 21 is the most common chromosomal abnormality in Indian babies, with 50 to 60 years of average life expectancy. 

Causes and Risk Factors of Down syndrome

Three factors contribute to the cause and risk factors of Down syndrome 

1. Abnormal chromosome division – Which chromosome causes down syndrome?

The human body is made up of billions of cells containing complete copies of our genetic information. The genetic information is nothing but the DNAs in the nucleus of each cell. The DNA molecule is packaged into thread-like structures, the chromosomes

Chromosomes Division

In general, we have 46 chromosomes in each cell that come in 23 pairs, and each chromosome in the pair is inherited from one parent (mother and father). 

Down syndrome is caused by an abnormal cell division entailing chromosome 21. Here, chromosome 21 has an extra copy making it a pair of three rather than two. This is why down syndrome is also referred to as Trisomy 21.

Down Syndrome - Chromosomes

2. Hereditary genetic disorder – How is Down syndrome inherited?

Genetics and heredity in rare cases can lead to a type of Down syndrome called Mosaic Down syndrome. The extra copy of chromosome 21 is passed from the parent shortly after conception. How early this occurs determines which cells will be affected. 

With mosaicism, a person has a mixture of cells with the usual 46 chromosomes and some with 27 chromosomes.

3. Age of the mother

Some research says that the higher the mother’s age during conception does contribute to the likelihood of a baby developing Down syndrome.

Age Of Mother Vs Down Syndrome

As a mother’s age increases, there is a possibility of errors happening in their chromosomes.

Down syndrome Symptoms

Most of the Down syndrome babies share the same physical features that, including:

  • Flattened facial features
  • Flat nose
  • Abnormally shaped ears
  • Short neck
  • Excess skin at the back of the neck 
  • Poor muscle tone
  • Almond-shaped eyes that slant up
  • Protruding tongue
  • Short neck
  • Loose joints
  • Tiny white spots on the iris of the eyes
  • A shorter thigh bone 
  • Broader forehead
  • Relatively small fingers 
  • Widely separated toes
  • A curved fifth finger

Down syndrome symptoms  also embrace certain behavioral and cognitive symptoms. This includes differences in IQ level, development delays, sleep troubles, extreme tantrums, and attention troubles.

Medical conditions and diseases in Down syndrome:

Congenital heart disease is one of the serious medical conditions found in a kid with down syndrome. This can be either mild (treated with medication) or, at times, severe that needs surgery.

People with Down syndrome are prone to diseases and infections due to abnormalities in their immune systems and physical features. Some of these include,

  • Vision problems
  • Hearing impairment
  • Hyperthyroidism
  • Gastrointestinal disorders
  • Epilepsy
  • Upper spine problem
  • Diabetes
  • Low Metabolic rate

Types of Down syndrome

Studies and research have classified three types of Down syndrome . It is impossible to tell the type of Down syndrome by just looking at a person. This is because all of them share similar symptoms and show variations in their chromosome karyotype, which can be identified during the confirmatory tests.

Types Of Down Syndrome

1. Trisomy 21: 

This is the most common type of Down syndrome, where all the cells in a human body carry an extra copy of chromosome 21. 

2. Translocation Down syndrome:

Translocation occurs in a small percentage of people affected with Down syndrome. Here, the cells have a complete or partial extra copy of chromosome 21 attached or “trans-located” to some other chromosome pair rather than 21. 

This type is further classified into two other subtypes – Familial and De nova. 

3. Mosaic Down syndrome:

Mosaic Down syndrome happens when the extra copy of chromosome 21 is passed from the parent early during conception.

People with Mosaic syndrome have a mixture of cells where some have the usual 46 chromosomes, and the rest have 27. This syndrome is described as a percentage that denotes the number of cells affected.  

The Mosaicism type has fewer Down syndrome features than the other two types, as not all cells are affected.

Down Syndrome Tests

Do you know when and how Down syndrome is diagnosed during pregnancy?

First, understand that a Down syndrome test  is not a one-step procedure to answer this question. There are two types of Down Syndrome tests taken during pregnancy.

Screening Tests:

First Trimester combined test:

By 11 to 14weeks of pregnancy, your doctor would suggest you undergo the following screening tests. 

  • Double Marker test: This is a blood test done to find the risk factors of chromosomal abnormalities in your baby by measuring the levels of two hormones – Pregnancy-Associated Plasma protein A (PAPP-A) and Beta-human Chorionic Gonadotrophin (beta-hCG). 

Nuchal Translucency (NT) scan: Nuchal Translucency  ultrasound scan measures the size of the fluid-like clear tissue found at the back of your baby’s neck. If this tissue level is more abnormal than expected, your baby might be at the risk of having chromosomal abnormalities.

Second Trimester test:

Quadruple test:

This blood test is done between 14 weeks and 20 weeks of pregnancy. A doctor recommends this to mothers who have missed their first-trimester screening tests. 

Chromosomal abnormalities are detected by measuring these four substances in maternal blood – Alpha-fetoprotein (AFP), Human Chorionic Gonadotropin (hCG), Estriol (uE3, and Inhibin A.

2. Diagnostic or Confirmatory Tests:

If your first or second-trimester screenings identify your baby at a high risk of a genetic disorder, you would be recommended to take one of the following three diagnostic tests.

Chorionic villus sampling (CVS): CVS is an invasive prenatal diagnostic procedure performed between the 11th and 13th weeks of gestation. 

Placental tissues are collected during this test to analyze the baby’s genetic makeup for chromosomal disorders.

CVS Procedure
Chorionic villus sampling

                                      Image courtesy: Babycenter

Amniocentesis

Amniocentesis  is again an invasive prenatal diagnostic procedure and is performed between the 15th and 20th weeks of gestation. 

The amniotic fluid is extracted from the uterus to analyze the baby’s genetic makeup for chromosomal disorders during this test.

Amniocentesis Procedure
Amniocentesis

                                       Image courtesy: Babycenter

Non-invasive prenatal test (NIPT)

NIPT  is a non-invasive test that involves taking a sample of the mother’s blood to examine the baby’s genetic makeup

NIPT
NIPT Blood Test

How is Down syndrome diagnosed after pregnancy?

After pregnancy, your newborn’s initial diagnosis of Down syndrome is made by analyzing the facial and other physical features. 

Some babies might show some of these facial features even without Down syndrome. Talk to your doctor about any tests for this if required.

Down syndrome Treatments

There is no medicine or single method to treat Down syndrome . The best way to make these kids behave better is by inclusion, while the rest depends on the individual kid’s physical and intellectual ability. 

There are four main types of therapies that result in better results for Down syndrome kids:

  • Physical Therapy
  • Speech and Language Therapy
  • Behavioural Therapy
  • Occupational Therapy 

Research says early intervention of these therapies is the key to getting the best results for these kids.

In addition to these therapies, advances in science and technology have led to discovery of many assistive devices to make life easier for these kids. 

How to Prevent Down Syndrome?

There are no preventive measures for Down syndrome. But, as a mother, you could follow certain measures that can increase the chances of giving birth to a healthy baby. 

  • Plan for pregnancy at the right age 
  • Avoid harmful and unhealthy habits during pregnancy
  • Choose healthy lifestyle
  • Don’t miss any follow-ups and medical procedures during pregnancy

You can also talk to your doctor and a genetic counselor if you’re at a high risk of having a baby with chromosomal abnormalities. You will be able to get the best advice on the tests and procedures available to you.

World Down Syndrome Day – March 21

Every year the voice of people with Down syndrome and those who support them has gone louder. 

March 21 is observed every year to celebrate World’s Down syndrome day  to mark the significance caused by the extra copy of chromosome 21. 

People started to understand that love doesn’t have anything to do with chromosomes and that there is nothing wrong with being unique.

FAQs

1. Which brain structures are impacted in individuals with Down syndrome?

Studies say people with Down syndrome have relatively smaller brain volume and a decreased white and gray matter in the frontal lobes and cerebellum of the brain. This is why individuals with Down syndrome have language, short-term memory, and other challenges. 

2. What is the life expectancy for Down syndrome?

In India, the life expectancy of people with Down syndrome is 50 to 60 years. Nevertheless, many people have successfully lived longer than this with the right therapies, lifestyle, and support.

3. Can stress cause Down syndrome?

Stress can’t be a direct cause of Down syndrome. However, a mother’s reaction to a stressful event can sometimes play a role.

4. Why are many people with Down syndrome obese?

Down syndrome, people have an increased risk of diabetes, sleep apnea, lower metabolic rate, and thyroid, which explains the relationship with obesity. 

5. Is it possible for a young (under 35 years old) mother to give birth to a Down Syndrome baby?

Despite studies showing that the risk factor increases with a mother’s age, it is always possible that a woman at a younger age can have a child with Down syndrome.