Table of Contents
Important Topic of Biology: Down’s Syndrome
Introduction
Down syndrome is a genetic disorder that results in various physical and mental disabilities. It is due to the presence of an additional chromosome 21 also known as trisomy of chromosome 21. Down syndrome is one of the leading causes of genetic disorders worldwide.
It is named after Dr. Langdon Down, who first noticed the condition.
In addition to physical symptoms and mental retardation, they can develop various diseases such as leukemia and Alzheimer’s. There is no cure, only quality of life can be improved with extra care and training to do important daily tasks. Down syndrome can be diagnosed during early pregnancy tests, which can reduce the risk of infection.
| S.NO | CONTENT |
| 1. | INTRODUCTION |
| 2. | DOWN SYNDROME CAUSES |
| 3. | DOWN SYNDROME TYPES |
| 4. | SYMPTOMS |
| 5. | DIAGANOSIS |
| 6. | FAQ’S |
Down Syndrome Causes
Down syndrome is a chromosomal disorder. It is due to autosome aneuploidy. There is one additional 21 chromosome or part of the chromosome present in all cells or cells.
The outbreak of Down syndrome is a live birth of 1: 800. The most dangerous factor is the mother’s age. Most cases of trisomy occur in a mother over 35 years of age.
Down syndrome is caused by abnormal cell division. During the division of mitotic cells and meiotic pairs, the chromosome separates so that each cell receives a copy of each chromosome. In down syndrome, chromosomes cannot separate, creating cells with an unequal number of chromosomes. This condition is called nondisjunction.
Nondisjunction occurs when the chromosome separates from the anaphase before all chromosomes ’kinetochores are attached to microtubules from different stems during metaphase. It results in one daughter cell having one small chromosome and another having one extra chromosome.
Down syndrome is also caused by the transfer of a chromosome component to another chromosome. The number of chromosomes is normal but one chromosome has an additional 21 chromosome component.
No genetic information is missing from these individuals but an additional copy of the genes of chromosome 21 causes abnormal physical and mental growth.
Down syndrome is usually not inherited. Translocation Down syndrome can be passed from parent to child. It may be hidden from the parent due to the unbalanced movement without symptoms but can transmit unequal transmission to the child and cause Down syndrome.
The life expectancy of a person with Down syndrome is about 60 years, depending on the number of health problems present.
Types of Down Syndrome
Down syndrome is of three types: Trisomy 21, Mosaicism, and Translocation
1. Trisomy of chromosome 21: Trisomy is the most common form of Down syndrome. About 95% of cases of Down syndrome.
There is one additional chromosome 21. The total number of existing chromosomes is 47 instead of the standard 46 chromosomes.
The main cause of trisomy is the failure of chromosome 21 at the time of meiosis during gamete formation. The abnormal cell with trisomy of chromosome 21 is fertilized resulting in trisomy in all embryonic cells.
2. Mosaicism: This is a rare form of Down syndrome, accounting for only 1% of total cases.
In Down Syndrome, some cells have 46 chromosomes and some cells have 47 abnormal chromosomes. Symbols may not be so prominent in mosaicism.
Mosaicism is caused when dissociation occurs during mitotic separation in the zygote after fertilization. It emerges from other normal cells and other cells with 21 trisomies.
3. Translocation Down Syndrome: This type of Down syndrome accounts for about 4% of the total incidence.
Here an additional chromosome 21 is missing but an additional portion of existing chromosome 21 is attached to a different chromosome. A total of 46 chromosomes exist, one of which is unusual.
This is due to the transfer of the long arm (q arm) of chromosome 21 to another chromosome during the multiplication process. The extra part is usually transferred to chromosome 14. Thus a person with translocation Down syndrome consists of one chromosome 14, one chromosome 14/21, and a normal chromosome pair 21. Its occurrence is not related to the mother’s age and may continue in families.
Symptoms of Down Syndrome
People with Down Syndrome experience any abnormalities. They were found to have physical and mental disabilities. The immune system is poor and prone to many diseases. They reach adulthood when they are older than usual. They are often found to be pregnant due to congenital heart disease, thyroid disease, sleep apnea, intestinal paralysis. They are at greater risk of contracting diseases such as leukemia and Alzheimer’s.
People with down syndrome can easily be identified by their body image and facial features. Gradually after birth, different symptoms begin to appear. Babies may be of normal size but as they grow older, their height is often much lower than that of the same age group.
The main symptoms of Down syndrome are:
- Short stem and curved growth
- Wrapping the skin above the eye, the eyes are tilted
- Tongue sticking out of the groin, flat-nose
- Mental retardation
- Heart failure
- One palm crease transverse with one hand wider and shorter
- Improper muscle tone and high flexibility
- Small head, short neck, and irregular teeth
- Delays in language development
- Mental retardation may be moderate to moderate
Diagnosis of Down Syndrome
Babies with Down syndrome can be diagnosed before or after birth.
Because of their unusual facial features, they are easily seen. When diagnosed after birth, there is no cure and only quality of life can be improved through training, education, and additional care.
Down syndrome can be diagnosed during pregnancy and if the fetus is diagnosed with Down syndrome, the pregnancy is terminated.
Down syndrome can be diagnosed through the amniocentesis process. In amniocentesis, amniotic fluid is removed with the help of a needle and a karyotype of dividing cells is made in the lab. Amniotic fluid cells have the same genetic makeup as a baby. The karyotype is investigated for any chromosomal abnormalities. If the karyotype is abnormal, the fetus is released.
FAQs
What is the meaning of down syndrome?
According to Down Syndrome definition biology, it is a chromosomal anomaly where the error of cell division leads to an additional copy of chromosome 21 in the body. It is divided into 3 types – Trisomy 21, Mosaic Down syndrome, and Translocation.
Q. What are the symptoms of down syndrome?
Ans: Down syndrome shows the following symptoms:
There may be physical symptoms such as short stature and small neck, flat nose bridge, lower muscle tone, lower eyes, large gap between first and second finger, tooth decay, thick teeth, etc.
The syndrome is also characterized by cognitive impairments such as mild or moderate cognitive impairment, delays in motor skills development and language development, etc.
How is Down syndrome diagnosed?
Down syndrome can be detected before birth or in newborns by genetic testing. Ultrasound examination may also be used during pregnancy, as the fetus with down syndrome shows delayed/absence of nasal growth (14-20 weeks of age) and anatomical biomarker symptoms of the disease (such as abnormal subclavian artery). Blood tests combined with other invasive techniques are known to improve the test result and diagnosis by 98.6% during the first trimester of pregnancy.
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