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Down syndrome, also known as trisomy 21, is a genetic condition characterised by the presence of a partial or full additional copy of chromosome 21 in an individual. Trisomy, by definition, is a disorder in which an individual has three replicates of a chromosome instead of two. Chromosomes are tiny units made up of DNA that contain the entire genetic makeup of an individual. These units play a significant role in determining a person’s physical traits and behaviour. The presence of extra genetic material in individuals with Down syndrome leads to the display of symptoms such as an upward eye slant, a small stature, and one deep crease on the palm. Each individual with Down syndrome may look similar and behave in a similar manner, but the severity of the condition varies from low to high. Some have serious developmental and intellectual disabilities while others lead a moderately healthy life.
Features of Down Syndrome
Down syndrome has distinct physical, cognitive (thinking), and behavioural features
Physical
• Flattened facial features, particularly the bridge of the nose
• Small head
• Almond-shaped, slanting-up eyes
• Small ears
• Short neck
• Protruding tongue
• Small white spots seen on the coloured part (iris) of the eyes, known as Brushfield’s spots
• Low muscle tone or loose joints
• Small feet and hands and short fingers
• Excessive flexibility
• Single line on the palm of a hand (palmar crease)
Behavioural
• Delays in speech and language development
• Low attention span
• Sleep difficulties
• Delays in cognition
• Stubbornness and tantrums
• Incoherence
The occurrence and severity of symptoms differ for each person having Down syndrome. A small percentage of individuals with Down syndrome is diagnosed with autism spectrum disorders, which affect their social interaction and communication skills. Some individuals also experience a decline in thinking ability with age and are at a high risk of developing Alzheimer disease and dementia.
Complications in Down Syndrome
Apart from the physical and behavioural impairments, individuals with Down syndrome are highly likely to develop certain health conditions, which include:
• Heart anomalies-About 50% of kids with Down syndrome develop a type of a congenital heart disease. This is one of the most commonly seen birth anomalies and may cause high blood pressure along with cyanosis (blue-tinted skin due to low oxygen levels in blood). These heart issues can be lethal and could necessitate an early-infancy surgery.
• Gastrointestinal defects-These defects can include anomalies of the oesophagus, intestines, anus, and trachea. Individuals are more susceptible to digestive problems, such as heartburn (i.e., gastroesophageal reflux), gastrointestinal blockage, or celiac disease.
• Hypotonia (poor muscle tone)-In the children with Down syndrome, rolling over, sitting, crawling, and walking are delayed due to poor muscle tone, which is combined with low strength. Children also tend to stick their tongue out more frequently, which affects their ability to feed properly depriving them of nutrients necessary for growth and development.
• Vision-related problems-In children having Down syndrome, more than 50% experience vision problems, such as cataracts, which can be present at birth. The risk of cataract increases with age. Other problems include crossed eyes, near-sightedness, and involuntary, rapid eye movements. Surgery or the use of glasses usually improves vision.
• Sleep apnoea-Significant pauses in breathing are caused due to skeletal changes and soft tissue, which lead to obstructed airways. Possible solutions to this include the removal of tonsils or using a continuous positive airway pressure device to allow smooth airflow during sleep.
• Blood disorders-There is an increased risk of developing leukaemia (cancer of white blood cells), anaemia (low iron in the blood), and polycythaemia (high red blood cell levels).
• Spinal problems-A few individuals present with misaligned top two vertebrae in their necks (atlantoaxial instability), which causes them to be at a high risk for injury to their spinal cord due to neck overextension.
• Hypothyroidism-Thyroid gland is responsible for secretion of hormones that regulate body temperature and metabolism. Hypothyroidism is caused due to less or no production of these hormones. It can cause fatigue, irritability, and fluctuating weight.
• Mental health conditions-Children with Down syndrome are prone to developing anxiety, depression, and attention deficit hyperactivity disorder (ADHD). They may also show symptoms such as aggression, psychosis, and social withdrawal. Coping with these symptoms in a positive way is quite difficult for individuals with Down syndrome, especially during adolescence.
Causes of Down Syndrome
Down syndrome is caused due to an error, called nondisjunction, that occurs during cell division. When a cell divides into two, a pair of chromosomes is split such that each cell has one chromosome. In nondisjunction, both chromosomes originating from the same pair enter one cell. This leads to the formation of the embryo with three chromosome-21 copies as opposed to the normal two. These errors occur randomly during sperm or egg formation. This additional genetic material causes the developmental inabilities in individuals with Down syndrome. There are no known causes for Down syndrome that can be linked to environmental factors or the behavioural activity of parents.
Three genetic variations may lead to Down syndrome.
These variations are as follows:
Trisomy 21
This Down syndrome type accounts for 95% of all cases. Before or at conception, one pair of the 21st chromosome, in either the egg or the sperm, does not separate, which leads to the replication of an extra chromosome in each cell of the embryo during development. All of the individual’s cells have an additional copy of chromosome 21, and this is known as complete trisomy.
Mosaic Trisomy 21
This type of Down syndrome is the least common and is accountable only for 2% of cases. Mosaicism, as the name suggests, occurs when two types of cells get mixed in the body. Some cells contain the normal 46 chromosomes whereas some have an extra chromosome making the count 47. Individuals with this variation generally have few typical Down syndrome characteristics.
Translocation
In this variation in cells, the overall number of chromosomes remains 46 but the additional chromosome 21 (either partial or full) gets attached (translocated) onto another chromosome before or at conception. This variation accounts for only 3% of cases.
It is possible for a parent without Down syndrome to have a translocation in their chromosome 21. Such a parent can pass this chromosome 21 on. Women above the age of 35 are at a higher risk having a kid with Down syndrome since an older egg has a high risk of undergoing defective chromosome division. The chances of a 35-year-old woman giving birth to a baby with Down syndrome are about 1 in 350 but these chances increase gradually to 1 in 100 by the age of 40.
Preventive Measures for Down Syndrome
There is no way one can prevent Down syndrome but consulting with a genetic counsellor is highly encouraged to understand the chances of having a child with Down syndrome, different kinds of prenatal tests, the advantages and disadvantages of testing, and methods to cope and adapt if one already has a child with Down syndrome.
Diagnosis of Down Syndrome
Down syndrome can be diagnosed either after birth or even during a pregnancy. During pregnancy, Down syndrome can be diagnosed using two tests:
Down syndrome can be diagnosed either after birth or even during a pregnancy. During pregnancy, Down syndrome can be diagnosed using two tests:
Prenatal Screening Test
These tests give information about the chances of a woman giving birth to a child with Down syndrome. These tests do not provide a sure shot diagnosis but rather only a probability. Although they are safer than diagnostic tests, screening tests normally involve an ultrasound (sonogram) and a blood test. The blood test measures for substances such as triple screen, MS-AFP, and quad screen in the blood of the mother. Blood tests are often accompanied with an ultrasound to check for markers, such as certain characteristics that have a significant association with Down syndrome. Another thing that is looked for during ultrasound is the fluid behind the neck of the baby. Excess fluid can be an indication of a genetic issue. Now, there are advanced prenatal screens that can be used to detect chromosomal material from the foetus that can be found in the mother’s blood. These tests are not invasive, but they cannot provide a definitive diagnosis.
Prenatal Diagnostic Test
These tests are often conducted after a screening test with positive results to diagnose Down syndrome. They are of various types as follows:
1. Chorionic villus sampling-It is performed between 11 and 14 weeks of pregnancy during the first trimester. A placental sample of chorionic villi is removed for testing.
2. Amniocentesis-It is usually performed in the second trimester, between 15 and 20 weeks of gestation. A sample of amniotic fluid, which is a fluid acquired from the sac that surrounds a foetus, is examined.
3. Percutaneous umbilical blood sampling–In this test, the blood taken from an umbilical cord is analysed.
These tests provide results for genetic abnormalities that would indicate Down syndrome. They have a 1% risk of causing a spontaneous miscarriage but can provide a diagnosis with nearly 100% accuracy.
Down syndrome can also be identified at birth by the presence of traits such as low muscle tone, a flattened facial profile, and upward slant to the eyes. Since these features may be present in a child without Down syndrome as well, a karyotype (chromosomal analysis) is done to confirm the diagnosis. Another test called fluorescence in situ hybridisation could be performed by mapping and visualising the genetic material in a person’s cells.
Treatment for Down Syndrome
There is no treatment for Down syndrome that will make the condition go away. Treatments available aim to improve the quality of life of individuals with Down syndrome and to spread awareness about coping with the condition. The purpose of this treatment is to treat the physical and cognitive challenges associated with the condition. Services such as speech, physical, and occupational therapy are offered and recommended throughout the early stages of a child’s life to allow them to reach their full potential by enhancing their physical and intellectual capabilities. Often times, healthcare providers recommend having a team of specialists, including speech therapists to help in developing communication skills, occupational therapists for making daily tasks easier, behavioural therapists to cope with emotional challenges, physical therapist to improve motor skills, primary care provides to keep a check on growth and development rate, and medical specialists such as cardiologists, geneticists, and eye specialists, depending on the specific needs of the individual.
Support and Resources
Having a team of trustworthy professionals and experts can make the parents of the child with Down syndrome feel at ease and better equipped to deal with the challenges they may face along the way. Parents may feel worried, anxious, stressed, scared and overwhelmed with the extent of decisions to be made and not knowing what to do. These are some steps that outline the important things that can be taken into consideration when raising a child with a Down syndrome:
• Finding out about schools and their educational accessibilities. Based on the child’s needs, which could be regular attendance of classes or special education or a mix of both, the school and a team of healthcare providers can work together to come up with the best option.
• Reaching out to other families who are also dealing with the same situation. There are a lot of support groups, both in person and online that can be a source of understanding and comfort especially for the parents. It may feel nice to be a part of a community who shares the same experiences.
• Encouraging independence can start as small as allowing your child to pack their own lunch or managing their dressing, but it allows for them to start being less dependent on their parents for everything.
• Contacting healthcare providers to know about intervention programs to work on the child’s motor, social, communication, and self-help skills.
There are a lot of organisations that offer support to individuals with Down syndrome and their families through various Down Syndrome Institutions across India. Some of which are:
• Down Syndrome Federation of India (DSFI) – https://downsyndrome.in/
• Amrit Foundation of India – https://amritfoundationofindia.in/
• Latika Roy Foundation – https://latikaroy.org/developmental-disabilities/down-syndrome/
• Global Down Syndrome Foundation – https://www.globaldownsyndrome.org/
The advances in medical technology have led to an increase in the life expectancy of individuals with Down syndrome with most living up to the age of 60 and some even longer. This has led to individuals being more and more integrated into mainstream society and organisations such as schools, work forces, healthcare systems. These individuals are capable of achieving optimal quality of life through parental care and support, medical guidance, and support systems that encourage inclusivity at all levels. Each individual with Down syndrome is different from the other and possesses a different degree of cognition, and coming to terms with this has allowed them to access their personal potential at their own pace.
