Down Syndrome: Human genetics are complex

Human genetics are complex. Most are aware that mutations in a gene can have catastrophic consequences. But what happens when there are extra copies. In the United States, 1 in every 7 babies born have Down syndrome—a genetic condition impacting almost every facet of life. Continue reading to learn everything you need to know about this genetic condition.

Down Syndrome: Human genetics are complex
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What Is Down Syndrome?

The human body is home to billions of cells. Each of those cells have chromosomes that contain genes, which determine inheritable traits passed down through two parents. Normally, there are 23 pairs of chromosomes to make a total of 46 chromosomes.

Down syndrome is a genetic condition that occurs when there is a partial or full extra copy of chromosome 21. The additional genetic material results in altered physical traits like a flat facial profile, slanted eyes, and low muscle tone, as well as intellectual and developmental delays.

Symptoms of Down Syndrome

Down syndrome has a variety of both physical and intellectual symptoms. They range from mild to severe depending on the individual.

Those with Down syndrome have a distinct appearance. Although it ranges in severity, the condition causes a combination of following bodily features:

  • Flattened Facial Profile—The bridge of the nose is especially flattened
  • Small Head—Other facial features such as the eyes, ears, and mouth are also small
  • Slanted Eyes—Almond shaped eyes slant upward
  • Short Neck—The neck typically has redundant skin folds
  • Brushfield Spots—Tiny white spots on the colored portion of the eye
  • Protruding Tongue—The tongue sticks out of the mouth
  • Palmer Crease—A single line across the palm of the hand
  • Sandal Gap—A groove between the first and second toes
  • Short Stature—Children and adults with Down Syndrome are shorter in height with small hands and feet
  • Clinodactyly—Pinky fingers that sometimes curve toward the thumb
  • Decreased Muscle Tone—Low muscle tone leads to loose joints

In some cases, Down syndrome affects more than physical features. It may be associated with dangerous congenital health problems in major organ systems.

  • Hearing Loss—The sense of hearing is compromised due to narrow ear canals and fluid in the ear
  • Heart Defects—Heart defects present at birth are common. Examples include atrioventricular septal defect or a hole in the heart
  • Sleep Apnea—Low muscle tone and narrowed airway passages are connected to sleep apnea, which is when breathing stops for periods of time while sleeping
  • Gastrointestinal Disorders—Disorders of the stomach and intestines occasionally occur.
  • Underactive Thyroid—The thyroid is a gland in the neck that releases hormones. Up to 15 percent of those with Down syndrome have an underactive thyroid.
  • Leukemia—Children with Down syndrome are likely to develop leukemia.
  • Atlantoaxial Instability—Misalignment of the top two vertebrae in the neck 

The early signs of Down syndrome consist of developmental delays, behavioral characteristics, and intellectual impairment. Being that communication is a struggle, some are non-verbal. Others, however, learn to speak fluently and engage in high rates of self-talk. Poor oral control is related to speech delays. Individuals with Down syndrome are also more prone to behavioral problems. They have frequent temper tantrums in comparison to their peers. Their IQ (intelligence quotient) is almost always below average.

Types of Down Syndrome

There are three types of Down syndrome. The type depends on the specific abnormal cell division during reproduction.

  1. Trisomy 21— All cells have three copies of chromosome 21. Trisomy 21 is the more prevalent form.
  2. Mosaic Down Syndrome—Only a portion of the body’s cells contain an additional copy of chromosome 21.
  3. Translocation Down Syndrome—Part of chromosome 21 translocates, or attaches, to another chromosome.

Causes and Risk Factors For Down Syndrome

As previously stated, Down syndrome is a genetic condition. Although it is a genetic condition, very rarely is it inherited. The greatest risk factor for having a baby with Down syndrome is the age of the woman at conception. Women aged 35 and older are likely to conceive a child with Down syndrome because their eggs are older, meaning the chance of improper cell division increases.

The circumstances in which Down syndrome may be inherited is when both the mother and father are carriers for the translocation form of Down syndrome. If families have one child with Down syndrome, the risk of conceiving another child with Down syndrome is greater.

How Down Syndrome Effects Cognition

Cognitive skills are the skills needed to think. Together, cognitive skills use information taken in via the senses from the environment to read, reason, pay attention, and more. Cognitive skills include attention, visual and auditory processing, memory, logic and reasoning, and processing speed. Down syndrome is associated with cognitive impairment, which means someone with Down syndrome has difficulty applying cognitive skills to learn. Learning with Down syndrome does not come easy. Most have mild to moderate levels of intellectual disability. Despite this, those with Down syndrome are capable of learning.


Delayed language development is a characteristic of Down syndrome. Speech and basic vocabulary falls below age level. The primary obstacles to language is failure to obtain sentence structure and grammar, as well as developing clear speech. This hinders communication. With early intervention services, most with Down syndrome eventually master language skills appropriate for their age. It is just very delayed.

Visual and Auditory Memory

Instructions given verbally are less likely to be retained due to short term auditory memory. To circumvent that issue, experts agree children with Down syndrome are visual learners. New information is more accurately retained when presented as images or other objects that can be seen.

Motor Skills

Along with other cognitive skills, motor development is also delayed in Down syndrome. Motor skills consist of the gross and fine movements of the muscles. Fine motor skills are movements controlled by the smaller muscle groups, whereas gross motor skills are connected to the larger muscles in the legs, arms, and abdomen. These motor skills are imperative to learning, but the delay prevents those with Down syndrome from exploring learning opportunities to the fullest potential. Additionally, poor oral control interferes with speech and language.

Psychological Concerns in Down Syndrome

Nearly 50 percent of people with Down syndrome have mental health concerns. While many of the psychological symptoms are the direct result of Down syndrome, others are caused by secondary mental and/or developmental illness. The most common are depression, anxiety disorders, attention deficit hyperactivity disorder (ADHD), oppositional defiant disorder, and even autism.

  • Disruptive, impulsive, inattentive, hyperactive and oppositional behaviors (raising concerns of coexisting oppositional disorder and ADHD)
  • Anxious, stuck, ruminative, inflexible behaviors (raising concerns of co-existing generalized anxiety and obsessive-compulsive disorders)
  • Deficits in social relatedness, self-immersed, repetitive stereotypical behaviors (raising concerns of co-existing autism or pervasive developmental disorder)


Depression is a mood disorder marked by unexplainable sadness persisting for two or more weeks. The signs and symptoms of depression are a lack of motivation, poor sleep, frequent crying, appetite changes, guilt, hopelessness, fatigue, and low self-esteem.

Down syndrome patients have limited communication abilities, especially younger children. At that age, it is not significant. However, adults and teenagers with Down syndrome are likely to suffer from depression because their inability to communicate effectively interferes with interpersonal relationships. They have increased difficulty in maintaining friendships, which furthers social withdraw, diminished interest in activities, and poor coping skills.

Anxiety Disorders

Children and adults with Down syndrome tend to possess a happy demeanor. However, they are at risk for transient episodes of anxiety that physicals diagnose as generalized anxiety disorder and obsessive compulsive disorder (OCD). Generalized anxiety is the a feeling of unease or anxiety that interferes with daily life for at least 6 months. The anxiety is connected to specific stressful events (i.e. a change in routine, the loss of a caregiver, transitioning between activities or daily tasks).

Obsessive compulsive disorder is a form of anxiety disorder in which excessive intrusive thoughts are alleviated by compulsions. Studies show the disorder occurs in up to 4.5 percent of those with Down syndrome (Prasher, 1995). The most common is OCD manifesting as obsessive cleanliness. A form of antidepressants known as selective serotonin reuptake inhibitors (SSRIs) is the firstline treatment in such patients.

Attention Deficit Hyperactivity Disorder (ADHD)

Attention deficit hyperactivity disorder is a condition characterized by hyperactivity, impulsive behavior, and inattention. It occurs in both children and adults. Those with Down syndrome have a higher incidence of these symptoms than the typical, healthy population. Many of the problems of focusing their attention on a single task is derived from abnormal information processing.

It is imperative to rule out other causes for ADHD-like symptoms. For example, in Down syndrome patients, this may look like vision or hearing problems that prevent the child from understanding directions (so, instead, their behavior comes off as inattentive). Gastrointestinal illness, a thyroid disease, communication problems, and sleep disorders may cause restlessness and other symptoms that mimic ADHD.

Oppositional Defiant Disorder

Oppositional defiant disorder is a behavioral disorder in children in teenagers that is related to repeated defiant behaviors. Someone with oppositional defiant disorder is blatantly defiant toward authority figures. They frequently exemplify patterns of anger, aggression, irritability, incessant arguing, and vindictiveness. Children and adults with Down syndrome are susceptible to this disorder. The defiance is not necessarily hateful, as it can be as simple as disregarding a caregiver’s command to sit down for dinner or participate in self-care habits like showering.The disorder is challenging to manage in those with significant communication and language barriers.

Down Syndrome Triggers for Behavioral Difficulties

Down syndrome is known to cause behavioral difficulties. According to the National Down Syndrome Society, those with Down syndrome are especially sensitive to the loss of close loved ones. They are prone to experiencing complicated grief. As they struggle to accept these intense feelings, they experience regression of cognitive abilities.

Any significant change in environment is also considered a stressor which triggers behavioral difficulties. In some instances, the behavioral challenges morph into mental illness such as depression, anxiety, or obsessive compulsive disorder. Researchers claim that behavioral problems should be thoroughly assessed to ensure an underlying medical condition (i.e. thyroid problems, sleep disorder, etc.) is not the offending culprit.

Diagnosing Down Syndrome

The majority of testing to confirm Down syndrome is done in-utero. Down syndrome can also be diagnosed at birth. If the baby displays the characteristic features, the doctor orders a genetic test to analyze the chromosomal karyotype. This blood test determines whether there is an extra chromosome present.

Prenatal Testing for Down Syndrome

Sequential integrated screening is a non-invasive screening for Down syndrome that carries no risk of miscarriage. To perform the screening, a blood sample is taken from the mother between 10 and 14 weeks of pregnancy. Next, an ultrasound measure the amount of fluid at the back of the baby’s neck. The combined results estimate the risk for Down syndrome.

Diagnostic tests are an increased accuracy, but present a risk for miscarriage. Aminocentisis is the most common to identify genetic disease prior to the baby’s birth. Around 15 to 20 weeks of pregnancy, amniotic fluid is removed through the mother’s abdomen with a needle and then the chromosomes are analyzed.

Chorionic Villus Sampling is similar to aminocentisis, However, it is performed around 10 to 12 weeks of pregnancy. Through ultrasound guidance, a piece of tissue is removed from the placenta. The sample is analyzed for its genetic chromosomal makeup.

Down Syndrome: Human genetics are complex
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Down Syndrome Treatment: Early Intervention

Down syndrome does not have a cure. Treatment focuses on addressing the symptoms through medical treatments for secondary conditions and early intervention. The term early intervention refers to services involving physical therapists, social workers, occupational therapists, speech therapists, and special educators. These services are implemented shortly after birth up until the age of 3. The specialists work together to prevent the extent of developmental and physical delays. For example, a physical therapist teaches certain exercises to increase existing muscle tone. Speech therapy assists Down syndrome patients to improve poor motor control, which encourages communication. While children with Down syndrome typically do not say their first words before age 2 or 3, speech therapy refines other skills necessary for speech. This is called “pre-speech” and consists of listening, visualizing the speaker, and making sounds. Occupational therapy is an integral component to early intervention because it demonstrates to the child how to become more independent.

Down Syndrome Prognosis

Experts have established that the average life expectancy for someone with Down syndrome is approximately 60 years old. Cognitive problems associated with age like as mild cognitive impairment and Alzheimer’s dementia tends to arise earlier in life. This specifically applies to memory loss, personality changes, and decreased intellect. Despite the further cognitive decline, heart disease and leukemia are the complications of Down syndrome that result in the most deaths. With proper interventions, those with Down syndrome can still have a productive life.


Guralnick, M. J. (2010). Early intervention approaches to enhance the peer-related social competence of young children with developmental delays: A historical perspective. Infants and Young Children, 23, 73–83.

Prasher, V.P. & Day, S. (1995). Brief report: Obsessive-Compulsive disorder in adults with Down’s syndrome. Journal of Autism and Developmental Disorders, 25, 453-458.

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