Down Syndrome 101
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Down Syndrome 101
This training provides an in-depth look at Down syndrome, from the biology behind Down syndrome to the accepted language one should use when discussing Down syndrome. Down syndrome is the most common chromosomal disorder. Unfortunately, many people don’t understand Down syndrome and this misunderstanding can be difficult to overcome.
By taking 15-20 minutes to complete this training, you’ll gain valuable knowledge about people who have Down syndrome. Included in the training are optional links to external resources where you can dig deeper into the information included in the training.
The Arc of Bartholomew County is a nonprofit organization aiming to be the resource of choice for individuals with intellectual or developmental disabilities and their families.
The organization was established in 1956 and continues to serve the community.
The training you're currently exploring was developed with the support of a Heritage Fund grant. The grant's goal was to expand online services and build resilience during the pandemic.
Training Introduction
This training introduces the most common chromosomal disorder: Down syndrome.
Introduction to Biology Terms
This section will define a few terms to help explain how Down syndrome occurs:
Chromosomes
Gametes
Zygotes
Meiosis
Aneuploidy
The Cell’s Nucleus
What are chromosomes?
Chromosomes are strands of DNA (short for deoxyribonucleic acid) found in the nucleus of nearly every cell in the human body. When the child does not have Down syndrome they'll inherit 23 chromosomes from each parent, for a total of 46 chromosomes.
As you'll learn in the rest of this training, Down syndrome is the most common chromosomal disorder. A single chromosome makes all the difference!
The National Human Genome Research Institute is a valuable resource if you'd like to learn more about chromosomes.
What are Gametes and Zygotes?
Gametes
Gametes are the cells each parent contributes during conception (i.e., sperm and ovum/egg cells). These cells are called haploid cells, meaning they only contain half of the required chromosomes.
Zygotes
Once the gametes combine, a zygote is formed. Irregularities in gametes could affect the viability of the zygote.
Down syndrome is unique chromosomal condition, the extra chromosome does not create a non-viable zygote. If the zygote is viable, then it's the first cell that will grow to form a brand new human!
Meiosis and Aneuploidy
Meiosis
Meiosis is a process of cell division. To improve the chances that offspring will survive, gametes are slightly (or significantly) different from one another. For Down syndrome, meiosis is often the point at which the extra chromosome is introduced. In the majority of cases, this seems to be a random occurrence.
Aneuploidy
If recombination errors occur during meiosis, then aneuploidy may result. Aneuploidy describes when the gamete has a different number of chromosomes than 23. Aneuploidy is one of the leading causes of miscarriages and developmental disabilities (source).
Three Types of Down syndrome
Down syndrome is not one-size-fits-all. We'll explain the three different types of Down syndrome in this section:
Trisomy 21 (Non-disjunction)
Chromosomal Translocation
Mosaicism or Mosaic Down syndrome
Trisomy 21 (Nondisjunction)
Trisomy means there's a third copy of a chromosome and, in the case of Down syndrome, it's the 21st chromosome. Nondisjunction means certain chromosomes weren't evenly divided during cell division (meiosis).
Trisomy 21 is the most common form of Down syndrome, affecting approximately 95% of all cases.
Other trisomy conditions exist and it's even possible that sex chromosomes can be affected by trisomy. The Wikipedia article about trisomy includes details about Trisomy 21 as well other trisomy disorders.
World Down Syndrome Awareness Day & Trisomy 21
Each year World Down Syndrome Awareness Day is celebrated on March 21st. The date, 3/21, helps you remember that Trisomy 21 creates a third copy of the 21st chromosome.
Chromosomal Translocation
The second most common form of Down Syndrome is related to a copy of the 21st chromosome, but this time that extra chromosome has moved or attached to a different location. Usually the extra 21st chromosome attaches to the 14th chromosome.
Translocation is far less common that Trisomy 21, affecting approximately 3% of individuals with Down Syndrome. Without genetic testing, it usually isn't possible to distinguish between a person with Trisomy 21 and chromosomal translocation.
Chromosomal Translocation and the Potential for Hereditary Transmission
Chromosomal translocation, in some instances, can be considered a hereditary form of Down syndrome. While much rarer than Trisomy 21, a parent could be what's known as a balanced carrier.
A balanced carrier is a person whose 21st chromosome is split into multiple pieces. A portion of the 21st chromosome could be connected to the 14th (the usual situation), while the remaining portion of the 21st is in it's typical location. The term balanced means that the total genetic information provides 46 chromosomes, so there aren't additional copies of the 21st. This means the parent won't have Down syndrome.
In a simplified example, the gamete from this parent may contain a full 21st chromosome and the 14th chromosome with an additional 21st chromosome attached. The child would then inherit a full 21st chromosome from each parent as well as an additional portion of the 21st chromosome connected to the 14th.
Given that the parent could pass along a 14th chromosome without the additional portion of the 21st, it's not a certainty that a child of a balanced carrier would have Down syndrome.
Mosaicism or Mosaic Down syndrome
The final type of Down syndrome is the least common, occurring in approximately 2% of cases. Mosaic Down syndrome means that some cells have extra copies of the 21st chromosome while other cells do not.
Mosaicism seems to occur at a later stage of development. If the zygote contained an extra copy of the 21st, it's more likely that the child would have Trisomy 21 than Mosaicism. There's still research to be done in this area.
Individuals with a small percentage of cells containing an extra chromosome often have fewer or less severe characteristics commonly associated with Down syndrome. For example, the characteristic facial features of a person with Down syndrome may not be present.
General Down syndrome Facts
The following section contains general facts about Down syndrome.
Is Down syndrome hereditary?
How common is Down syndrome?
Down syndrome's correlation with the birth mother's age
The Down syndrome Advantage
Longevity of people with Down syndrome
Is Down syndrome hereditary?
Hereditary, at a basic level, means something passed from parent to child. Genetic disorders, on the other hand, are usually caused by random mutations or environmental factors.
In most cases Down syndrome is not hereditary.
Down syndrome, resulting from chromosomal translocation, could be passed along to a child. However, this is a far less common occurrence than Trisomy 21.
How common is Down Syndrome?
Currently, Down syndrome is the most common chromosomal disorder. According to the Centers for Disease Control (CDC), Down Syndrome occurs in approximately 1 in 700 births (source). This means about 5,500 babies are born each year with Down syndrome.
To add some perspective to that number, the lifetime risk that a male gets breast cancer is 1 in 833 according to the American Cancer Society.
Rare events aren't easy to compare since they happen so infrequently. Even the most common chromosomal disorder is a relative rare event.
Down Syndrome Prevalence Increases with Mother's Age
Evidence suggests that mothers who give birth later in life are more likely to have children with Down syndrome.
When mothers give birth prior to age 30, the prevalence of Down syndrome is relatively even. Approximately 7 in 10,000 births result in a child who has Down syndrome.
When the mother is between 30 and 34, the rate increases to approximately 11 in 10,000 births. For mothers between 35 and 39, it rises to 26 in 10,000 births. Finally, mothers who are 40 years old and older, evidence suggests about 82 in 10,000 live births will produce a child with Down syndrome.
Despite the increase in prevalence for mothers 35 and older, the majority of women have children prior to their 35th birthday. Given that reality, nearly 80% of babies born with Down syndrome come from mothers who are under 35 years old (source).
The Down syndrome Advantage
Since it's likely that parents of children with Down syndrome are older, a concept called the Down syndrome Advantage has been popularized.
Older parents are more likely to have the financial means to avoid being adversely affected by the additional costs of raising a child with Down syndrome.
Longevity of People with Down syndrome
The life expectancy of a person with Down syndrome continues to increase. An average child born with Down syndrome was expected to live to about 10 years old in 1960.
In 2007, the average life expectancy increased to 47 years (source). Today, average life expectancy has increased to 60 years old (source).
The Language of Down Syndrome
This section will give you an understanding of current language relating to Down Syndrome. The conscientious use of language promotes inclusive social understanding and promotes deeper understanding.
People-First vs. Diagnosis-First Language
Down's vs. Down Syndrome
The R-Word
People-First vs. Diagnosis-First Language
The language we use to describe people affects our perception about them. We choose to place importance on the person or the diagnosis based on the order of words in our description.
In reference to a Down syndrome diagnosis, people-first language would be: a person with Down syndrome. Alternatively, diagnosis-first language would be the following: a Down syndrome baby.
The Arc of Bartholomew County promotes and encourages the use of person-first language rather than diagnosis-first language.
Down syndrome vs. Down's syndrome
According to the National Down Syndrome Society, the proper way to refer to this diagnosis is Down syndrome.
The possessive (Down's) implies ownership by the condition which doesn't align with the reality of these individuals.
The R-word
Language is a representation of our culture. It changes constantly and is a tool for both help and harm.
Labels and stereotypes simplify group identification and understanding. Until you look behind the labels being used, you have a limited view of the truth behind the label. The (often hidden) assumptions labels convey make them powerful.
Referring to individuals as "retarded" is pejorative. It labels a person as lesser and reduces them to a label that cannot encompass their unique abilities.
Challenges of Down Syndrome
This section explores some of the challenges associated with Down syndrome:
Social
Health & Sensory
Financial
Social Challenges for Parents of Children with Down syndrome
When an expectant parent is told that his or her child may have Down syndrome, it's an emotional moment. It's a life-changing piece of unexpected information.
At that time, it's important for medical professionals to avoid influencing the parent. Subtle facial expressions may indicate that the parent should feel a certain way about the news. Even well-meaning medical professionals may imply a preferred future outcome.
This is the first social challenge faced by expectant parents whose child may have Down syndrome: the pressure to participate in prenatal testing during pregnancy.
When parents do decide to participate in prenatal testing, the second social challenge becomes apparent. Now that the information is available, what will the parent do?
Informed and uninformed opinions may be offered from well-meaning family members, medical professionals, and even complete strangers. Pressure to decide an outcome for the pregnancy is ever-present when the outcome of prenatal testing is shared.
Directive vs. Non-Directive Medical Advice
Directive medical advice is advice where an individual is told (directed) to take a certain action. Alternatively, non-directive medical advice provides medical evidence and information without encouraging one action over another, when a particular action isn't medically necessary to preserve life.
Medical professionals may inadvertently encourage parents, who undergo prenatal testing, to terminate the pregnancy when there's an increased likelihood of the child having Down syndrome.
Questions like: "Are you going to keep the baby?" imply that having an abortion is on equal footing with taking the pregnancy to term. The tone and body language included with that question often reveals the opinion held by the person posing the question.
A person in such a position of authority, like a doctor, has an extraordinary influence on the expectant parent. Given the political, moral, and philosophical nature of such a decision, it's wise for medical professionals to take extreme care when discussing results of prenatal testing with a parent-to-be.
Health Challenges of Down syndrome
Congenital Heart Defects (CHDs)
Approximately 50% of all babies born with Down syndrome have CHDs (source). A CHD is one marker for Down syndrome that medical professionals may observe during ultrasounds. CHDs vary in severity, some will require surgery while others will resolve themselves as the baby grows.
Early onset and increased risk of Alzheimer's Disease
Individuals with Down syndrome have an increased risk of developing Alzheimer's disease earlier than those people who don't have Down syndrome.
It's estimated that "Alzheimer’s disease affects about 30% of people with Down syndrome in their 50s. By their 60s, this number comes closer to 50%." (source). In the United States six million individuals have Alzheimer's disease (source). The prevalence of Alzheimer's disease, in the United States, is approximately 10% for individuals 65 and older (source).
So, individuals with Down syndrome are three to five times more likely to experience Alzheimer's compared with the rest of the population.
Obesity, Lower Metabolic Rate, and Reduced Thyroid Function
According to a study from 2004, women with Down syndrome are more likely to be overweight or obese compared to women without Down syndrome. Men with Down syndrome were more likely to be overweight, but were less likely to be obese (source).
The study compared individuals with Down syndrome to individuals without Down syndrome who were the same gender, age, and had similar occupations.
Sensory Challenges of Down syndrome
Vision Issues
Over half of individuals with Down syndrome experience vision issues. Special care and attention must be paid in the early years of life to identify and address potential eye disease.
Less serious vision issues, typically resolved with eye glasses, are "hyperopia (farsightedness), astigmatism, or myopia (nearsightedness)." Individuals with Down syndrome also may experience "weak accommodation (difficulty changing the focusing power of the eye from distance to near)." Problems with tear ducts may require manual massage during the first year of life for a child with Down syndrome.
A common condition known as "Strabismus (eye misalignment)" may also be present. If left unaddressed Strabismus can lead to "amblyopia (loss of vision also known as lazy eye) and loss of stereopsis (the use of the two eyes together, or depth perception)."
Individuals with Down syndrome may have cataracts at birth. If cataracts are missed, then it's possible that the person's vision won't develop appropriately and may cause irreparable damage.
The National Down Syndrome Society shares an interview that goes in depth about vision issues facing individuals with Down syndrome: https://www.ndss.org/resources/vision-down-syndrome/
Financial Challenges of Down syndrome
Marginally Higher out-of-pocket Healthcare Costs During Childhood
A 2016 study (pdf) explored the additional healthcare cost families incur when raising a child with Down syndrome: "On average, parents of children with [Down syndrome] pay an additional $84 per month for out-of-pocket medical expenses when costs are amortized over 18 years."
The CDC has shared the results of a similar study from 2014 on its website. This study indicated that median hospital costs varied dramatically during the first year of life based on the presence and severity of congenital heart defects (CHDs).
Children with isolated Down syndrome, defined as children who didn't have a CHD or other major birth defect, had significantly lower healthcare costs during the first years of life when compared to children with Down syndrome who had other birth defects.
