Down syndrome is one of the more commonly known genetic conditions. It is also known as Trisomy 21, Trisomy G, 47XX+21, 47XY+21, and Down’s in different cultures. It is a chromosomal condition where the individual has three copies of chromosome 21 instead of the usual two. The presence of the third copy causes the different medical concerns and developmental characteristics that we see in these individuals.
What caused it?
In most individuals with Down Syndrome, the cause is a chance occurrence. There are some factors that can increase the risk of this happening such as increased maternal age. However, parents of any age have the chance of having a child with Down Syndrome.
In some individuals, the cause is called a translocation mutation, meaning that apart from the two copies of chromosome 21 that is usually present, a part of chromosome 21 also attached to another chromosome during the formation of a reproductive cell in a parent or very early in fetal development. This can occur in eggs or sperm cells. The baby then ends up having the third copy of chromosome 21.
In a very small percentage of individuals with this syndrome, they have some cells that have only two copies of chromosome 21 and there are some cells that have three copies of chromosome 21. These people are classified as having mosaic Down Syndrome. These individuals typically have characteristics of the syndrome manifesting in slightly different ways as compared to the first two groups discussed.
What are the features of a child with Down Syndrome?
Children with Down Syndrome have distinct physical features. These include upward-slanted palpebral fissures, epicanthal folds, brachycephalic head, low set ears, Brushfield spots, flat midface with low nasal bridge, extra skin over the nape area, short necks, larger tongue, single transverse crease on their palms, and wider spaced first and second toes.
More than the outward physical features, doctors are also concerned about the inner physical features that can cause medical complications. Individuals with Down Syndrome are usually hypotonic – meaning they have lower muscle tone. This is important because it can affect everything from their feeding, breathing, sleeping, and movement. They can also have smaller airways that can affect their breathing and predisposition to having respiratory symptoms. Smaller ear canals predispose them to have more ear infections, which can cause hearing impairment if not addressed promptly. They often have vision problems, cardiac issues, gastrointestinal, hormonal, and some have hematologic (blood) concerns. Medical management of these concerns will often involve specialists, and a medical referral is strongly advised.
In children with Down syndrome, doctors anticipate that developmental problems and delays may occur due to the physical attributes in this population. As previously mentioned, having low tone may impact the development of gross (arms and legs) and fine motor (hands and fingers) movements. This translates to having delays in sitting, crawling, walking, and running. As a child grows, doctors will monitor how stable they are and this may impact the ability of these children to join more active physical activities, which in turn may impact their social activities with peers. This can be a particular struggle as these children tend to be very social and some are very affectionate individuals. The decrease in physical activity can also predispose these children to suffer from obesity when they get older, bringing with it its own set of medical complications.
There are delays in language that commonly occur in this population. It may partly be attributed to the co-occurrence of intellectual disability (please see global developmental delay for a more comprehensive discussion) in most of these individuals, but may also be attributed to the physical characteristics that are present. Children with Down Syndrome are known to have relative strengths in visual-spatial perception and processing, but have a relative weakness with language and verbal working memory. They are also better at using expressive language (e.g. verbally and expressing thoughts and ideas) than they are with receptive language (e.g. understanding what is said to them). This means that in a child struggling to follow verbal instructions or conversations, the use of sign language and gesturing may help them comprehend and communicate better. Physical differences may also impact their language development as those with larger tongues and hypotonic (low tone) oral muscles may have more difficulty pronouncing words and may be less understood by adults and their peers. This may cause others to interact with them less and limit their opportunities for practicing verbal means of communicating with others.
As previously mentioned, their low muscle tone can also affect their sleep. These children tend to snore and may have obstructive sleep apnea (interruptions in a person’s breathing as he/she sleeps). This has developmental consequences apart from medical consequences. In a child with poor sleep, behavioural, attentional, and cognitive challenges may arise. Children may be perceived as more irritable or hyperactive, unable to concentrate and stay on task, and have difficulty in pursuing activities that are cognitively demanding. In a child who already has intellectual disability, and a temperament and behaviour that is perceived to be stubborn and has a proclivity for non-compliant behaviours (commonly associated with Down Syndrome), effects of poor sleep can compound these problems.
Other conditions that co-occur with Down syndrome include attention deficit and hyperactivity disorder (ADHD) and obsessive-compulsive disorder (OCD). When these conditions are also present, transitions (shifting from one activity/routine to another) and behaviour compliance may become even more challenging. In those who have the inattentive type of ADHD, safety issues increase as children with Down Syndrome are also known to have a tendency to “wander off”.
The risk of premature cognitive decline as an individual ages is increased in Down Syndrome. As adults, they have a higher risk of being diagnosed with Alzheimer’s disease. Transitioning to adult medical care well is important and should be planned during early adolescence.
How is Down Syndrome diagnosed?
Down syndrome is diagnosed through genetic testing for the presence of a third chromosome 21. In areas where genetic testing is not available, clinicians may diagnose based on the physical features present in the child. It is still best to confirm the diagnosis through genetic testing when able.