What's Down Syndrome?

March 8, 2018

This morning, a darling little girl with Down syndrome, a student in our preschool, stood outside our administrative offices and told us all story after story.  Some of them involved dancing, some were action-packed, some were simply explanatory.  We didn’t understand most of the words that streamed from this animated little performer, but we knew what she was talking about, because: personality.


Increasingly visible in the media today, Down syndrome is quickly becoming one of the most instantly recognizable developmental diagnoses in the United States.  But how much do we really know about it?


This post will help to answer some basic questions about Down syndrome.  The more we know, the more we can do to promote the welfare of the community of people affected by this syndrome.


So What Is Down Syndrome?

 

The simple answer is that Down syndrome is a genetic chromosomal disorder.

 

Our bodies are made up of cells, and those cells construct our bodies based on the blueprints of genetic material found on our chromosomes, in the nucleus of the cell.  Typically, every cell in our bodies will carry 23 pairs of chromosomes in its nucleus.  One set is inherited from each parent, and each chromosome lines up with its match inside the nucleus, until a marching platoon of chromosomes is ready to build a human being.


Down syndrome occurs when one of those chromosomes (not to name names, but *cough* chromosome 21 *cough*) brings a buddy: a full or partial extra copy of chromosome 21 in some or all of a person’s cells.


In 1866, John Langdon Down published a scholarly work describing his work with a patient who had Down syndrome.  His was the first physician’s study of the syndrome that designated it as a distinct condition all its own, with common characteristics and effects.  This work is why the syndrome now bears his name, and why some refer to Down as the “father” of the syndrome.


However, Down did not discover the syndrome – its distinct characteristics were well known and recognized in several cultures for centuries.  People with Down syndrome had been referenced in literature, art, and science many times prior to Down’s publication.  Now we know that the syndrome has appeared in skeletal records in archaeology, some evidence possibly indicating its existence as long ago as the 5th century (1600 years ago!).


Down’s work was only the first in a long line of research into this condition.  It was Jérôme Lejeune, a French physician, who first identified Down syndrome as a chromosomal condition.  It was he who observed the extra 47th chromosome that is present in the cells of individuals with Down syndrome in 1959, the defining characteristic that was later identified as the direct cause of the syndrome itself.


More recently, an international team of scientists set to work identifying and cataloguing every gene on chromosome 21, no small task since there are about 329 of them.  They finished the job in the year 2000, and their achievement has brought great advances in research about Down syndrome.


What Causes It?


Doctors have identified three ways Down syndrome can occur, all having to do with that extra copy of chromosome 21, each with slightly different effects and characteristics.


The most common type of Down syndrome, accounting for 95% of cases, is Trisomy 21.  Also called “Nondisjunction,” Trisomy 21 is simply the scientific term for when the nucleus of a cell is carrying an entire extra copy of chromosome 21.  Three of chromosome 21 = Trisomy 21.


In Trisomy 21, one pair of 21st chromosomes fails to separate within the egg or sperm, possibly even prior to conception.  This means that once the embryo begins to grow and develop, its blueprint already contains the extra chromosome, and the tag-along is then replicated in every cell of the body.


Another type of cause is Translocation, which makes up about 4% of all instances of Down syndrome.  In this version, the third full or partial copy of chromosome 21 has a falling out with its twins, and goes to hang out with another chromosome (usually chromosome 14).


Interestingly, in Translocation, this extra 21 replaces the matching version of whichever chromosome it attaches to, so there is actually only the usual number of 23 pairs of chromosomes in this type.  But because there is still a third copy of 21, just hiding while it tries to balance out the wrong chromosome, Down syndrome still appears.


Rarest of all, there is a third type of Down syndrome known as Mosaicism which comprises the remaining 1% of all cases.  In this type, some of the individual’s cells contain the usual 46 chromosomes, but some contain that extra copy of chromosome 21.


Because only some of the body’s cells are affected, this rarer type is harder to diagnose, and the usual characteristics of Down syndrome vary widely from person to person.  People with Mosaic Down syndrome often have fewer or milder characteristics than those with the other, more common types, but every individual experiences Down syndrome differently, and it is impossible to pigeonhole any one type as being more or less severe.


As far as research has been able to determine, the cause of these extra chromosomes is entirely genetic, and not fully understood.  There is no significant link to environmental factors, nor to parents’ activities prior to conception and birth.  The full copy of a 21st chromosome can come from either parent, with approximately 5% of cases originating with the father.


The only known correlation between an external factor and the development of Down syndrome has to do with the mother’s age.  Above age 35, the chance that a mother will give birth to a baby with Down syndrome gradually increases, from about 1 in 350 at age 35 to about 1 in 30 by age 45.  However, even with this increasing probability, 80% of children with Down syndrome are born to women under 35 years of age.


What Does It Do?


Beyond the sometimes distinct facial appearance, Down syndrome tends to cause small hands and feet, a single strong crease across the palm, small pinky fingers that sometimes curve toward the thumb, and poor muscle tone or loose joints.  Down syndrome has also been associated with a small stature both as children and adults.


There may be a cognitive component to some cases of Down syndrome.  Many individuals with Down syndrome experience cognitive delays, but the intellectual disability is usually moderate or mild, and may even be barely noticeable.


Down syndrome comes with many co-occurring conditions and susceptibilities.  It is these conditions that can be more severe, while the syndrome itself usually causes only mild complications.  Congenital heart defects are strongly linked to Down syndrome, for instance, as is an occurrence of Alzheimer’s disease in older individuals.


Hearing and vision impairment are common among individuals with Down syndrome.  People with Down syndrome may also develop smaller sinuses and tear ducts than a child who is typically developing, so they can be very prone to respiratory problems and infections.  There are also less common co-occurring conditions linked with Down syndrome.


Of course, every individual is uniquely affected by Down syndrome, and abilities and characteristics will differ widely from person to person.


What About Treatment?


There is no single, standard treatment for Down syndrome.  Individuals can be affected in so many different ways and on so many different levels that it is impossible to devise a one-off prescription that will work for every case, not even on a small scale.


Early invention is key!  Quite a bit of research has shown that early intervention significantly improves progress and outcomes for children with Down syndrome.  The following infographic shows some of the ways therapy can help a child with Down syndrome to reach their full potential.

Advances in science and medicine have greatly improved the quality of life for individuals who have Down syndrome.  Just since 1983, these improvements have increased the average life expectancy of people with Down syndrome from just 25 years to 60 and older!  Most individuals with Down syndrome are able to live a fully-integrated, high-functioning lifestyle throughout adulthood.


So What Does Success Look Like?


Success is different for every child.  Since every child’s abilities and needs are unique to their situation, the ways in which they leap those hurdles are equally as unique.


For one of our friends, learning to walk was a significant hurdle.  She was two years old and had not even really attempted walking.  She was content to be carried, or to sit where you put her and draw all focus to that spot.  So when she began to stand up and take wide, shuffling steps, it was a huge day!  Now she sashays and parades around the preschool hallways like she owns the place (she kind of does).


For another friend, simply learning to hold a pouch of food and use a straw was a pretty huge leap forward.  Because he was unable to process solid food, he had been spoon-fed his lunches since he arrived at the preschool prior to learning that skill.  But he is now on his way to eating at least some of his meals independently.


Here in Middle Tennessee, there are many opportunities to get involved, and resources for families and children affected by Down syndrome.  The Down Syndrome Association of Middle Tennessee, Buddy Walks, Gigi’s Playhouse Down Syndrome Achievement Centers and other organizations and events in the Nashville area continue to shine a light in the community, promoting acceptance of and education about people with Down syndrome.


With increasing opportunities in career choices, including jobs in the retail and food service industries, performing, modeling, and chances to compete in the Special Olympics, people with Down syndrome in today’s landscape are capable of anything they set their minds to.

SOURCES:

 

[1] Centers for Disease Control and Prevention. Facts about Down Syndrome. 21 November 2017. Web. 23 February 2018. <https://www.cdc.gov/ncbddd/birthdefects/DownSyndrome.html>.
 

[2] National Down Syndrome Society. Down Syndrome. 2018. Web. 23 February 2018. <https://www.ndss.org/about-down-syndrome/down-syndrome/>.
 

[3] National Human Genome Research Institute. Learning About Down Syndrome. 29 June 2017. Web. 23 February 2018. <https://www.genome.gov/19517824/>.


[4] National Institute of Child Health and Human Development. What Are Common Treatments for Down Syndrome? 31 January 2017. Web. 23 February 2018. <https://www.nichd.nih.gov/health/topics/down/conditioninfo/treatments>.

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