A Guide to Down Syndrome

Updated September 25, 2019

This article was scientifically reviewed by YourDNA

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A list of references is also included at the bottom of this article.

What are Trisomies?

To better understand the origins of Down syndrome, it is essential to become familiar with the role that trisomies play in this condition.

A trisomy is a type of polysomy. A polysomy is a condition that is found in several species (including plants, insects, mammals, etc.) where there may be three or more copies of a chromosome.

What's in this Guide?

Disclaimer: Before You Read

It is important to know that your genes are not your destiny. There are various environmental and genetic factors working together to shape you. No matter your genetic makeup, maintain ideal blood pressure and glucose levels, avoid harmful alcohol intake, exercise regularly, get regular sleep. And for goodness sake, don't smoke.

Genetics is a quickly changing topic. Read More...

Usually, there are only two chromosomes that are passed on in a cell's structure.

Specifically, a trisomy is a condition where there are three instances of a chromosome instead of two. A trisomy is considered a type of aneuploidy, defined as the presence of any abnormal number of chromosomes.

In a human, normally there are 46 chromosomes. Of these, 23 are passed on from the mother, and 23 are passed on by the father.

If the chromosome pairs do not separate properly during cell division, the egg or sperm may end up with a second copy of one of the chromosomes.

There are different kinds of trisomies 1.

  • Full trisomy also called primary trisomy, means that an entire extra chromosome has been copied.
  • Partial trisomy means that there is an extra copy of part of a chromosome.
  • Secondary trisomy means the extra chromosome has quadruplicated arms
  • Tertiary trisomy means that the extra chromosome is made up of copies of arms from two other chromosomes.

Trisomies can take place in any chromosome, and different trisomies will produce different kinds of abnormal conditions. Often, trisomies result in miscarriage instead of a live birth.

Trisomies can be characterized as autosomal trisomies, also known as trisomies of the non-sex chromosomes.

When this happens, they are described by referencing the specific chromosome where the trisomy occurred.

For example, the presence of an extra chromosome 21, found in Down syndrome, is also known as Trisomy 21.

The most common types of autosomal trisomies that survive to birth in humans are:

  • Trisomy 21 (Down syndrome)
  • Trisomy 18 (Edwards syndrome)
  • Trisomy 13 (Patau syndrome)
  • Trisomy 9
  • Trisomy 8 (Warkany syndrome 2)

Autosomal trisomies can be associated with congenital disabilities, intellectual disabilities, and shortened life expectancy.

What is Down Syndrome?

Down syndrome occurs when an error in cell division results in an extra chromosome 21.

Usually there are 46 chromosomes in every cell. Of these, 23 are inherited from the mother, and 23 are inherited from the father.

In Down syndrome, there are three copies, either complete or partial, of chromosome 21.

A person who has Down syndrome can have impacted physical growth and cognitive abilities, and mild to moderate developmental issues.

There is also a higher risk of some health problems such as Alzheimer's disease, heart disease, gastrointestinal disorders, and epilepsy.

Overall, Down syndrome occurs in about 1 in every 700 pregnancies 2. Certain factors may increase or decrease the frequency at which Down syndrome may present itself.

For example, research has shown that there is a higher propensity for Down syndrome in a child if a mother is older than 35 years of age 3.

Before age 30, Down syndrome appears in fewer than 1 in every 1,000 pregnancies. After age 40, this figure rises to about 12 out of every 1,000 pregnancies 4.

Doctors can screen for Down syndrome both during pregnancy and after birth.

Characteristics and Intellectual Disabilities of Down Syndrome

There are several distinct physical features and developmental issues associated with someone who has Down syndrome.

Some of the physical characteristics of a person with Down syndrome include:

  • eyes that slant upward, have oblique fissures, have epicanthic skin folds on the inner corner, and have white spots on the iris.
  • low muscle tone
  • loose joints
  • short stature
  • short neck
  • small ears
  • a protruding tongue
  • flat nasal bridge
  • small hands and feet
  • short fingers
  • broad, short hands with a single crease in the palm
  • small pinky fingers that sometimes curve toward the thumb
  • single, deep creases across the center of the palms
  • a large space between large and second toe
  • a single flexion furrow of the fifth finger
  • excessive flexibility

Developmental and intellectual issues associated with Down syndrome include:

  • an IQ in the mildly-to-moderately low range
  • cognitive development that will vary widely from person to person
  • reaching developmental milestones on a delayed basis compared to peers (i.e. learning to talk)
  • delay in developing fine motor skills because it takes longer to develop gross motor skills.
    On average, a child with Down syndrome will:
    • sit at 11 months
    • crawl at 17 months
    • walk at 26 months
  • problems with attention
  • a tendency to make poor judgments
  • impulsive behavior
  • slower to speak than other children
  • short and long-term memory is affected

Related Health Issues

People with Down syndrome may also develop other health problems more frequently. Some of these health problems can include:

  • congenital heart defects (impacts about half of all people with Down syndrome)
  • gastrointestinal defects including abnormalities of the intestines, esophagus, trachea, and anus. There is also a higher risk of developing digestive problems, such as GI blockage, gastroesophageal reflux, or celiac disease.
  • dementia with signs and symptoms that may begin around age 50
  • respiratory problems
  • hearing difficulties
  • obesity
  • spinal problems due to a misalignment of the top two vertebrae in the neck
  • obstructive sleep apnea
  • ear infections
  • eye diseases
  • Alzheimer's disease
  • childhood leukemia
  • epilepsy
  • thyroid conditions
  • endocrine problems

The flip side of this is that there appears to be a lower risk of hardening of the arteries, diabetic retinopathy and most kinds of cancer.

Different Types of Down Syndrome

There are three types of Down syndrome. It can be challenging to tell the difference between each type without looking at the chromosomes because physical features and behaviors are similar.

Trisomy 21 is the most common type of Down syndrome, accounting for 95% of all diagnoses 5.

It occurs when there are three, instead than two, number 21 chromosomes in every cell of the body. The abnormal cell division takes place during the development of the sperm cell or the egg cell.

This means that instead of the usual 46 chromosomes, a person with Down syndrome has 47.

This additional genetic material alters a person's development and causes the characteristics associated with the syndrome.

Translocation accounts for 4% of all cases of Down syndrome and occurs when part of chromosome 21 breaks off (translocated) during conception or cell division and attaches to another chromosome 6.

In most cases, it is chromosome 14. The total number of chromosomes in a person's cells remain at 46, but the presence of an extra part of chromosome 21 causes the characteristics of Down syndrome.

Mosaicism accounts for about 1% of all cases of Down syndrome. It occurs when the nondisjunction of chromosome 21 takes place in one – but not all – of the initial cell divisions after fertilization 7.

As a result, there is a mixture of two types of cells. Some contain the usual 46 chromosomes and others contain 47 chromosomes.

There are no known behavioral or environmental factors that cause Down syndrome.

The Genetics of Down Syndrome

Down syndrome is a genetic disorder caused by a mistake in cell division during the early development of the fetus.

The abnormal cell division results in an extra full or partial copy of chromosome 21, and it is this extra genetic material that causes the physical and developmental characteristics associated with Down syndrome.

It is the most common genetic chromosomal disorder and cause of learning disabilities in children.

Most of the time, Down syndrome is not inherited. The exception to this is when Translocation Down syndrome is passed from parent to child.

However, this is quite rare since only about 4% of those with the condition have Translocation Down syndrome. Also, of those, only some inherit it from their parents.

When balanced translocations are inherited, the mother or father has some rearranged genetic material from chromosome 21 on another chromosome, but there is no extra genetic material.

This means the parent has no signs or symptoms of Down syndrome but can pass an unbalanced translocation on to children, causing Down syndrome in the children.

Risk Factors for Down Syndrome

Certain risk factors place a child at higher risk of being born with Down syndrome. Those risk factors include:

  1. Maternal age. The older a woman is the greater the chances of giving birth to a child with Down syndrome. This is especially true after a woman turns 35 years old because older eggs have a higher risk of improper chromosome division. Although a woman's risk of conceiving a child with Down syndrome increases after 35 years of age. Most children with Down syndrome are born to mothers under 35 because younger women have far more babies.
  2. Being carriers of the genetic translocation for Down syndrome. Both men and women can pass the genetic translocation for Down syndrome on to their children.
  3. Having had one child with Down syndrome. Parents who have one child with Down syndrome and parents with a translocation themselves are at a higher risk of having another child with Down syndrome.

Diagnosis of Down Syndrome

People who have higher risk factors of having a child with Down syndrome might receive screening and diagnostic tests.

A person can be checked for Down syndrome during pregnancy or after a child is born. There are two types of tests for Down syndrome during pregnancy.

A prenatal screening test can show an increased likelihood that a fetus has Down syndrome, but it cannot determine Down syndrome is definitely present.

Prenatal screening tests for Down syndrome are conducted several ways.

  • A blood test and an ultrasound test during the first trimester of pregnancy. This is the most conventional approach for screening during the first trimester and allows a doctor to check for markers (certain proteins) in a mother's blood that may suggest the presence of Down syndrome.

    If this is the case, an ultrasound test is performed to create images that can detect fluid at the back of a fetus's neck. This ultrasound test is called the measurement of nuchal translucency.
  • A blood test during the second trimester of pregnancy. This blood test also enables a health care provider to check for markers in the mother's blood.

    A triple screen looks for levels of three different markers; a quadruple screen looks for levels of four different markers.
  • A combined test. This is also sometimes called an integrated test and uses a blood test and an ultrasound during the first trimester, as well as a second-trimester blood test.

    Results are combined to produce one Down syndrome risk rating.

If a woman is pregnant with twins or triplets, a blood test will not be as reliable because the substances from a Down syndrome fetus may be harder to detect.

When a screening test shows an increased likelihood of Down syndrome, a diagnostic test can be ordered to determine with certainty that it is present.

Screening tests include:

  • Nuchal translucency testing. At 11–14 weeks, an ultrasounds measures the clear space in folds of tissue behind the neck of a developing fetus.
  • Triple screen or quadruple screen. At 15–18 weeks, this measures the quantities of various substances in the mother's blood.
  • Integrated screen. Combines results from first-trimester blood and screening tests, with or without nuchal translucency, with second-trimester quadruple screening results.
  • Cell-free DNA. A blood test that analyzes fetal DNA in the mother's blood.
  • Genetic ultrasound. At 18–20 weeks, doctors combine a detailed ultrasound with blood test results.

When screening tests turn up positive results, more invasive diagnostic tests may be required.

The drawback with diagnostic tests is that they can increase the risk of miscarriage, fetal injury, and preterm labor.

Diagnostic tests are usually performed inside the uterus and can include 8:

  1. Chorionic villus sampling. At 8–12 weeks, a doctor might obtain a tiny sample of placenta for analysis, using a needle inserted into the cervix or the abdomen.
  2. Amniocentesis. At 15–20 weeks, they may obtain a small amount of amniotic fluid for analysis, using a needle inserted into the abdomen.
  3. Percutaneous umbilical blood sampling. After 20 weeks, a small sample of blood is taken from the umbilical cord for analysis, using a needle inserted into the abdomen.

These tests look for changes in the chromosomes that would indicate a Down syndrome diagnosis.

Screening and diagnostic tests cannot predict the full impact of Down syndrome on a baby.

There is no way to predict the severity or specific elements of the presentation of Down syndrome before birth.

Who Should Consider Testing for Down's Syndrome?

There is no way to prevent Down syndrome. Consult with a genetic counselor if you are at a higher risk than normal for having a child with Down syndrome or have already had a child with Down syndrome 9.

A genetic counselor will be able to provide you with important information about the risks you face, the chances of having a child with Down syndrome and what tests you may want to consider, as well as the pros and cons of each.

Treatments and Care Options for Down Syndrome Patients

Because each person with Down syndrome has different needs, strengths, and limitations, there is no single standard of treatment for someone with the condition.

Down syndrome is a lifelong condition and it is crucial to start treatment and services early in life to help improve a child's physical and intellectual abilities as soon as possible.

This is the best way to help a person develop their full potential within the limits of their case of Down syndrome.

By doing so, they can take up an active and more independent role in the community.

Early intervention begins shortly after birth and often continues until a child reaches age 3.

After that age, most children receive interventions and treatment through their local school district.

To promote independence and productivity, treatment services can include:

  • Physical therapy to build motor skills, increase muscle strength, and improve posture and balance. This is especially important early in a child's life when physical abilities lay the foundation for other skills
  • Speech-language therapy improves communication skills and use language more effectively, offsetting the fact that Down syndrome children often learn to speak later than their peers. In many cases, children with Down syndrome understand language and want to communicate before they can speak.

    A speech-language therapist can help a child use other means of communication, such as sign language and pictures until he or she learns to speak. A therapist may help with conversation skills, pronunciation skills, comprehension, and learning and remembering words.
  • Occupational therapy finds ways to adjust everyday tasks and conditions such as eating, getting dressed, writing, and using a computer.

    At the high school level, an occupational therapist could help teenagers identify jobs, careers, or skills that match their interests and strengths.
  • Emotional and behavioral therapies find appropriate responses to both desirable and undesirable behaviors.

    Children with Down syndrome may have difficulty communicating, may develop compulsive behaviors, and may have Attention Deficit Hyperactivity Disorder and other mental health issues.

    These therapists try to understand why a child is acting out and create strategies for avoiding or preventing these situations from occurring.

    The changes in hormone levels during puberty can cause more aggressive behavior and a therapist can help teenagers recognize their intense emotions and teach them healthy ways to calm down.

Some people with Down syndrome also take amino acid supplements or drugs that affect their brain activity.

Clinical trials revealed adverse effects from this protocol and to date, no medications for Down syndrome have demonstrated an appreciable degree of safety and efficacy.

Children with Down syndrome may also need extra help or attention in school, although many children are included in regular classes due to a trend in recent years of seeking to mainstream children with Down syndrome.

If not, specialized schools are available.

In many cases, children with Down syndrome can be helped by assistive devices which can be any type of material, equipment, tool, or technology that enhances learning or makes tasks easier to complete.

This might include amplified devices for hearing problems, bands that help with movement, special pencils to make writing easier, touchscreen computers, and computers with large-letter keyboards.

A person with Down syndrome may routinely need to see physicians, special educators, speech therapists, occupational therapists, physical therapists, and social workers.

In addition, people with Down syndrome are at a greater risk for developing related health issues, and they will need to be monitored and treated specifically for those problems as they develop.

For example, an infant with Down syndrome may need surgery early in life to correct a heart defect; or a person with Down syndrome may have digestive problems that require a lifelong special diet.

Federal Law and Down Syndrome

Most children with Down syndrome are eligible for free and appropriate public education under Public Law 105-17.

The Individuals with Disabilities Education Act (IDEA) makes it possible for children with disabilities to get free educational services and devices to help them learn as much as they can.

Each child is entitled to these services from birth through the end of high school, or until age 21, whichever comes first.

Most early intervention programs fall under this legislation.

Each child must be taught in the least restrictive environment that is appropriate.

This does not mean that each child will be placed in a regular classroom. Educators must work to provide an environment that best fits the child's needs and skills.

If a child qualifies for special services, a team of people must work together to design an Individualized Educational Plan (IEP) for the child.

The National Early Childhood Technical Assistance Center, run by the U.S. Department of Education, provides information and resources for parents and families looking for early intervention programs.

Visit the Early Childhood Technical Assistance Center for more information.

Other early intervention resources are available at Day2DayParenting.com and at FamilyVoices.org.

The U.S. Department of Education also funds the Parent Center Network, which provides resources, contacts, and assistance for parents and families trying to navigate special education programs.

The Prognosis for Down Syndrome

The individual prognosis for someone with Down syndrome varies greatly depending on the severity of the condition.

However, due to advancements in treatment, in general, Down syndrome patients are living much longer.

It is not uncommon for someone with Down syndrome to live to 55 or 60 years old, and in many cases, people live much longer.

The quality of life for Down syndrome patients still remains difficult at times, but with a trend toward early intervention and more efforts to mainstream children when possible, integration and the ability to lead a healthier life is more widely accepted than ever.

While Down syndrome cannot be prevented or cured, research continues with the hopes that advancements in genetic engineering may one day be able to unravel the mystery of Down syndrome and find ways to either mitigate its impacts or solve the DNA riddles that surround it.

What to do Next: Living with Down Syndrome

For additional information on Down syndrome, contact the following organizations:

Down Syndrome Research Foundation (DSRF)
DSRF initiates research studies to better understand the learning styles of those with Down syndrome.

Global Down Syndrome Foundation
This foundation is dedicated to improving the lives of people with Down syndrome through research, medical care, education and advocacy.

National Association for Down Syndrome
Provides support for all persons with Down syndrome in achieving their full potential. They seek to help families, educate the public, address social issues and challenges, and facilitate active participation.

National Down Syndrome Society (NDSS)
NDSS seeks to increase awareness and acceptance of those with Down syndrome.

DS-Connect®: The Down Syndrome Registry
Parents and families of children with Down syndrome can connect with other families and people with Down syndrome from around the world to learn more and share information.

This safe and secure registry helps families and researchers identify similarities and differences in the symptoms and treatment of people with Down syndrome and guide future research.

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Referenced Sources

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    Wikipedia.org. Retrieved online, August, 2019.
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    By Peter Crosta. Reviewed by University of Illinois-Chicago, School of Medicine. Last updated Wed, 6 December 2017.
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    By Peter Crosta. Reviewed by University of Illinois-Chicago, School of Medicine. Last updated Wed, 6 December 2017.
  5. THREE TYPES.
    Down syndrome Association of Central Ohio. Retrieved online, August 2019.
  6. THREE TYPES.
    Down syndrome Association of Central Ohio. Retrieved online, August 2019.
  7. THREE TYPES.
    Down syndrome Association of Central Ohio. Retrieved online, August 2019.
  8. Facts about Down Syndrome.
    Division of Birth Defects and Developmental Disabilities, NCBDDD, Centers for Disease Control and Prevention. Page last reviewed: February 15, 2018.
  9. Down Syndrome.
    Stanley J. Swierzewski, III, M.D. healthcommunities.com. Last Modified: 14 Sep 2015.