Jacob, a child with Down Syndrome, enjoying a family holiday and browsing in shops, like any other 5 year old child wouldJacob looking at books and watching TV at age 6 years - Down Syndrome doesn't stop normal development, but social attitudes do. - Jacob, a baby with Down Syndrome - Jacob at one year of age


The cause of Down Syndrome is one of ever deepening understanding. The most salient cause of Down Syndrome has been attributed to the mother’s age – but it’s not really the most important, it’s just one of many Down Syndrome risk factors.

But, let’s start with the basics first and then go on to the more advanced understanding of the cause of Down Syndrome.

CONTENTS: 1… CAUSES and TYPES OF DOWN SYNDROME – The Extra Chromosome 21 —  2… It’s all the women’s fault, the sticky chromosome theory — 3… Father’s age plays a significant role in the cause of Down Syndrome — 4… Protein BubR1, when in insufficient amounts, can cause an increase in still births and birth defects, such as Down syndrome.

Jacob, age 6, is a kid with Down Syndrome and loves doing just about everything other kids his age do. The cause of Down Syndrome is an extra copy of chromosome 21

1… CAUSES and TYPES OF DOWN SYNDROME – The Extra Chromosome 21

1a. Down Syndrome – Trisomy 21

The straight forward biological cause of Down Syndrome, is the extra chromosome 21. This, by definition, is Down Syndrome – if you have that extra chromosome 21, you have Down Syndrome, it is the absolute certain cause of Down Syndrome.

At conception – at the coupling of egg and sperm – something goes wrong, resulting in the fertilised egg having three chromosome 21’s; aka trisomy 21 ( tri – meaning three). A normal baby only has two chromosome 21’s.

1b. MOZAIC Down Syndrome

Occassionally an aberration occurs, when the egg fertilises correctly, but as it divides again and again, an error in replication occurs and part of the baby has an extra chromosome 21 in the cells. When this later error occurs, the kid is said to have ” mozaic Down Syndrome ” – mozaic referring to the mixture of normal and Down Syndrome cells.

People with mozaic Down Syndrome will be affected only to the extent of the body areas involved; some may go their whole life unaware of their Down Syndrome partial make up – for others, their Down Syndrome component may be quite extensive affecting them markedly.

Mozaic Down Syndrome accounts for about 3% of those with Down Syndrome.

1c. Down Syndrome – Translocation Trisomy 21

About 4% of people with Down Syndrome have ” translocation trisomy 21 “, which refers to the translocation of part of chromosome 21 to another chromosome. In this instance, there are only two copies of chromosome 21 in the individual, but another chromosome is also carrying a part of chromosome 21, which in turn can also cause Down Syndrome.

1d. Why was it called Down Syndrome and what do we know about the chromosome?

Where did the term Down Syndrome come from? A doctor, John Langdon Down, identified a cluster of symptoms in some people, this cluster of symptoms (aka syndrome) was named after him, hence the term Down Syndrome.

So, having covered the rudimentaries, lets now try and understand the cause of Down Syndrome a bit better.

More about the biological genetic cause of Down Syndrome: Dr. Antonarakis et al, year 2002, Chromosome 21 has been found to contain 184 genes. Nineteen more genes than previously thought.

Pevsner, year 2003, we still don’t know which genes or processes cause the neurological changes we see in Down Syndrome.

Roger Reeves et al., year 2004, states it is now clear that no single gene is responsible for the changes that Down Syndrome causes. It may be possible, from what we are learning from mice, to modify the genetic expression of the extra third chromosome in people with Down Syndrome, thereby effectively reducing or eliminating the damaging changes.



2… It’s all the women’s fault. The sticky chromosome theory.

Our obstetrician informed us that the cause of Down Syndrome was the increasing chromosomal abnormalities that occur with age: The chromosomes are lined up in pairs in the egg before the mother is even born. The older the mother gets, the more ‘sticky’ the chromosomes get. So that when the time for them to divide occurs, the more likely with age that they will divide unevenly, taking material from, or losing material to, the other chromosome in the pair.

When the egg divides unevenly and takes an extra “chromosome 21”, we have the simplistic cause of Down Syndrome. There is no way yet known that can counteract this cause of Down Syndrome, so vitamin supplements etc are also useless in preventing this.For the statistics on age of mother and age of father etc as it relates to risk of a Down Syndrome pregnancy just click here This simplistic sticky theory cause of Down Syndrome, however, is not the whole picture. Read on to get a better understanding of the cause of Down Syndrome, as we know it today.


3… Since that theory, research has since shown that the father’s age plays a significant role in the cause of Down Syndrome.

Gone are the days of the mother having to take all the guilt – if you’re a mother, I think you know what I’m talking about. Now the cause of Down Syndrome is seen in terms of the mother’s and father’s age.

When both mother and father are into their mid thirties, early forties, both are some how unwittingly linked to an increased risk of a Down Syndrome pregnancy.

The authors of this fabulous study are unable to clarify why the age factor is so important.

We can, however, surmise that there is something that goes wrong, that translates into Down Syndrome; that this error is more than likely common to both the female egg and to the male sperm. Something is changing in these as our bodies get older. One lot of scientists believe they may have the answer:


4… Dr. van Deursen et al, year 2005. The cause of Down Syndrome appears to be rather simple thing:

As you may know, as people grow older they also tend to develop genetic and chromosome errors, in their eggs if female and in their sperm if male. If you want to know more about this, you can check out our web page on Down Syndrome Risk Factors in Pregnancy and check out section 4 and the fertility notes provided there.

According to Dr. van Deursen, based on his and others research on ovarian BubR1 protein in mice, he concludes that this protein may be the cause behind age-related infertility, as well as a cause of some birth defects in babies. This is because we have the equivalent same gene producing said protein. The researchers appear to suspect that this protein, when in insufficient amounts, can cause an increase in still births and birth defects, such as Down syndrome.

Is this, the cause of Down Syndrome, finally answered?

May be, but there is much more research that is going to have to happen, to know for sure and to provide an effective remedy, at least for preventing Down Syndrome.

Just think, one day you may be able to take a tablet or have an injection, knowing that this will prevent the genetic error without forgoing or killing the kid. What a blessed day that will be. But, when that last person with Down Syndrome dies, our world will be less perfect.

Finally – Translocation Trisomy 21 – Are you a genetic carrier of Down Syndrome? Is a rare cause of Down Syndrome and we have a page devoted to it.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.