What is Down Syndrome?
Did you know there is at least one case of Down syndrome in every 700 pregnancies? Research also suggests that the older a mother, the more likely she is to give birth to a child with Down syndrome. However, there are several other factors that are also deemed responsible for giving rise to this disorder. Understandably, this turns out to be a vital topic that must be understood by every student of Biology.
Read along to find more about the Down syndrome symptoms, features, and types!
The Down syndrome definition describes it as a chromosomal disorder, wherein, an error in cell division leads to an extra copy of chromosomes in the body. This extra chromosome 21 tends to affect the physical and cognitive abilities of affected individuals.
Additionally, individuals with Down syndrome often run a higher risk of suffering from various health disorders. Notably, it is not a disease rather a term that best describes the features which arise due to it.
On that note, let us proceed to find types of Down syndrome and their differences.
Types of Down Syndrome
Typically, there are 3 types of Down syndrome –
Trisomy 21
It is the most common of the three types and accounts for almost 95% of the cases. It is mostly caused by the irregular separation of chromosome 21 during meiosis either in egg cells or sperm. When the fertilized egg develops, it transfers an extra copy of this chromosome to each cell in the body.
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Translocation
It accounts for 4% of the total cases. It must be noted that in this particular type, the extra chromosome is transferred to new cells differently.
It occurs only when a significant part of chromosome 21 breaks off amidst the replication process and gets attached to another chromosome. This leads to a cell with 46 chromosomes and a little extra chromosome 21.
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Mosaicism
This particular type accounts for as little as 1% of the total cases. Notably, in this form, the error in separation takes place right after the egg is fertilized.
The role of timing is the most noteworthy here. Also, the fact that not all cells have an extra chromosome makes the symptoms of mosaic Down syndrome less prominent.
Do It Yourself: Define Down syndrome and mention its types.
Down Syndrome Features
These are some Down syndrome features –
A. Physical Features
Small stature with a short neck
Flat nasal bridge
low muscle tone
Eyes slant upwards
Eyes have an additional fold on the upper eyelid
A large gap between the large and second toe
B. Cognitive Features
Intellectual disability ranges from mild to moderate level
Delay in learning to speak
Delay in motor skills
Problematic attention span
Other than these, individuals with Down syndrome are prone to health problems like – congenital heart defect, epilepsy, respiratory disorders, hearing difficulty, leukemia, Alzheimer’s, thyroid, etc.
One can diagnose this anomaly through a screening test and other prescribed diagnostic tests.
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Test Your Knowledge: Highlight the differences between the 3 types of Down syndrome.
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Management of Down Syndrome
There can be several efforts such as early childhood intervention, screening for common problems and medical treatment wherever indicated, a good family environment, and work-related training can improve the development of children with Down syndrome. Education and proper care have been known to improve the overall quality of life. A parent must accept the challenges and the reality that raising a child with Down syndrome is more work for parents than raising an unaffected child. Other than the above-mentioned steps, typical childhood vaccinations are recommended.
Health Screening
Health organizations have largely recommended screening those with Down syndrome for particular diseases so that the affected can be provided with adequate medical aid.
At birth, all children affected with Down syndrome are advised to get an electrocardiogram and ultrasound of the heart. In many cases, surgical intervention for the treatment of heart problems may be required (as early as three months of age). In adult patients, heart valve problems may occur and further ultrasound evaluation is essential in adolescents and those in early adulthood. As there is an elevated risk of testicular cancer, some doctors recommend yearly examination of testicles in male patients.
Cognitive Development in Down Syndrome
Hearing aids or other amplification devices have been found to be useful for language learning in those with hearing loss. Training and speech therapy is recommended to be started as early as possible (around nine months of age).
Enrollment in educational programs to assist learning and social interaction before reaching school age may be useful. Children of school-going age diagnosed with Down syndrome can benefit from inclusive education (whereby students of differing abilities are placed in classes with their peers of the same age), provided some adjustments are made to the curriculum to suit their individual needs. Evidence to support this, however, seems to be weak. In the United States, due to the Individuals with Disabilities Education Act of 1975, public schools are required to generally allow attendance by students with Down syndrome and create a more inclusive ethos for persons of disability.
Individuals with Down syndrome learn better through visual aids. There still may be persistent difficulty in children with down syndrome in creating sentence structure and grammar and face ability to speak clearly but early intervention can help with cognitive development. Motor skills can be enhanced through the use of physical therapy, speech and language therapy, and occupational therapy. Physical therapy primarily focuses on motor development and teaching children to interact with their environment. Speech and language therapy helps prepare them for lingual abilities. Lastly, occupational therapy can be provided to help with skills needed for independence in later life.
FAQs on Down Syndrome
1. What is Down Syndrome and how does it occur biologically?
Down Syndrome is a genetic disorder caused by the presence of an extra copy of chromosome 21. It occurs due to a chromosomal non-disjunction during the formation of gametes, which leads to three copies of chromosome 21 instead of the usual two. This additional genetic material results in the distinctive physical and cognitive features associated with Down Syndrome.
2. What are the three main types of Down Syndrome and how are they different?
The three main types of Down Syndrome, covered in the CBSE Biology syllabus, are:
- Trisomy 21: Caused by non-disjunction, leading to three copies of chromosome 21 in all cells (about 95% cases).
- Translocation Down Syndrome: Part of chromosome 21 attaches to another chromosome, but the total chromosome number remains 46 (accounts for around 4% cases).
- Mosaic Down Syndrome: Some cells have an extra chromosome 21, while others do not (about 1% cases). Symptoms tend to be milder.
3. What physical and cognitive features are typically seen in individuals with Down Syndrome?
Common physical features include:
- Short stature
- Flat nasal bridge
- Low muscle tone
- Upward slanting eyes with an epicanthal fold
- Single crease across the palm
- Wide gap between the first and second toes
Cognitive features include:
- Intellectual disability (mild to moderate)
- Delayed speech and language development
- Learning difficulties and short attention span
4. How is Down Syndrome diagnosed before and after birth?
Prenatal diagnosis involves screening tests such as ultrasound and blood tests to detect markers for Down Syndrome. Definitive diagnosis is done by karyotyping through procedures like amniocentesis or chorionic villus sampling. Postnatal diagnosis confirms the condition using a chromosome analysis (karyotype) of the baby's blood sample.
5. What are the primary health risks associated with Down Syndrome and how are they managed?
Individuals with Down Syndrome are at higher risk for:
- Congenital heart defects
- Hearing and vision problems
- Thyroid disorders
- Leukemia
- Epilepsy
- Respiratory infections
Early medical intervention, routine screenings, regular cardiac evaluations, and therapies like speech and occupational therapy help manage these health issues effectively.
6. Why does maternal age increase the risk of having a child with Down Syndrome?
The risk of non-disjunction (chromosomal separation error) increases with maternal age, especially after age 35. Older egg cells are more prone to errors during meiosis, which raises the likelihood of an extra chromosome 21 being present in the offspring.
7. How can inclusive education help children with Down Syndrome, and what adjustments are usually needed?
Inclusive education allows children with Down Syndrome to learn alongside their age-matched peers, promoting social and cognitive development. Successful inclusion often requires adjustments such as:
- Modified curriculum and teaching methods
- Use of visual aids and hands-on activities
- Support from special educators and therapists
8. Compare the features and impact of Trisomy 21 and Mosaic Down Syndrome.
Trisomy 21 affects all cells and generally presents more pronounced physical and cognitive symptoms. Mosaic Down Syndrome affects only a portion of the cells, often resulting in milder features. Early diagnosis and intervention play key roles in the management of both types.
9. What common misconceptions exist about Down Syndrome that are important to address among students?
Common misconceptions include thinking that Down Syndrome is a disease (it is a genetic condition), or that it can be cured (it cannot). Additionally, not all individuals have the same severity of symptoms, and with support, many lead productive, fulfilling lives.
10. How does early intervention influence the development and quality of life in children with Down Syndrome?
Early intervention with speech, physical, and occupational therapy greatly improves motor skills, communication, and self-care abilities in children with Down Syndrome. This enhances their independence, academic performance, and overall quality of life.
