Understanding Down Syndrome - An Overview
Genetic Disorder- Down syndrome is caused by a genetic abnormality, specifically the presence of an extra chromosome 21, also known as trisomy 21.
Physical & Mental Disabilities- It leads to various physical and mental disabilities, affecting overall development.
Common Genetic Disorder- One of the most prevalent genetic disorders worldwide, widely recognised and studied.
Named After Langdon Down- The condition was first observed by physician Langdon Down.
Mental Impairment- Individuals with Down syndrome may experience intellectual disabilities and developmental delays.
Health Complications- Increased susceptibility to other conditions such as leukaemia (blood cancer) and Alzheimer’s disease.
No Cure Available- There is no cure for Down syndrome, but proper care, training, and support can enhance the quality of life.
Early Diagnosis Possible: Prenatal screening can detect Down syndrome during early pregnancy, helping in early intervention and management.
Reasons for Down Syndrome
Down syndrome is a genetic disorder caused by the presence of an extra copy of chromosome 21, making it a chromosomal disorder.
It results from aneuploidy of the autosome and occurs in approximately 1 in 1800 live births, with higher risks in mothers over 35 years.
Down syndrome arises due to abnormal cell division (nondisjunction) during mitosis or meiosis, leading to unequal chromosome distribution in daughter cells.
During anaphase, chromosome 21 fails to separate properly, causing one cell to have three copies (trisomy 21) while another lacks it.
In some cases, part of chromosome 21 translocates to another chromosome, resulting in extra genetic material without changing the total chromosome count.
Down syndrome is characterised not by missing genetic material but by an extra portion of chromosome 21, leading to physical and mental developmental abnormalities.
As it is clear that Down syndrome is genetic, it is also non-inheritable in most cases. In cases where the abnormality is caused due to a problem in genetic translocation rather than an entirely new chromosome being present, Down syndrome is inheritable. In such cases, the signs and symptoms of down syndrome may be absent in the parent but can be passed on to the child. The child can go on to live for another 60 years. But this also depends on the number of other health complications present.
Types of Down Syndrome
Down syndrome disease can be classified into three types. All the three types explained above as part of the theory are distinctly given below in points.
Trisomy of Chromosome 21- This is the general case when there is an extra copy of chromosome 21 present in the cells. This makes the total number of chromosomes from 46, the normal case, to 47, the abnormal one. This is explained earlier, which happens because of the nondisjunction of chromosome 21 during the anaphase segregation of chromosomes. Because of this, Down syndrome is also known as Trisomy or Trisomy 21.
Mosaicism- This accounts for one percent of the total cases of down syndrome disease. Usually, this case arises when the nondisjunctions happen during the mitotic division of the zygote into blastomeres. It causes some cells to have a normal number of chromosome 21 while some cells have an abnormal number of chromosome 21.
Translocation Down Syndrome- As said, this condition arises when a part of chromosome 21 is translocated to another chromosome (usually chromosome 14). It does not end in an extra chromosome 21 copy but some part of the long arm of chromosome 21 as part of chromosome 14. Nevertheless, it can cause down syndrome disease when expressed in a dominant form. The translocation of the down syndrome doesn't have any correlation with the mother’s age.
Signs and Symptoms of Down Syndrome
There are various physical and mental abnormalities in a person suffering from Down syndrome. One example is those that have poor immunity and hence are subjected to many diseases. Their development takes place at an age later than normal. Many of the patients are born with congenital heart defects, thyroid disease, sleep apnea, and gastrointestinal defects. They are also more susceptible to diseases like leukaemia and Alzheimer's than normal people.
The physical and facial features are the easiest signs of Down syndrome. After the child is born, the signs and symptoms of Down syndrome start appearing. At first, the infants may be of normal size, but when they grow slowly, their height grows much less than those of the same age. The prominent signs and symptoms of Down syndrome are
Short height and undersized growth
Slanted eyes and folding in the skin above the eye
Flattened nose and furrowed tongue
Mental retardation
Heart deformities
Broad and short hand
Poor toning of the muscle with excessive flexibility
Short neck, small head and abnormal teeth
Longer time in developing linguistic abilities
Mild or moderate cognitive impairment
Down Syndrome Diagnosis
Children with Down syndrome can be diagnosed before or after birth.
Postnatal Diagnosis (After Birth)
Babies with Down syndrome have peculiar facial features, making them easily identifiable.
There is no cure after birth, but their quality of life can be improved through training, education, and extra care.
Prenatal Diagnosis (Before Birth)
Down syndrome can be detected during pregnancy. If the foetus is found to have the condition, pregnancy is often terminated.
The most reliable test for diagnosis is Amniocentesis.
Amniocentesis – How It Works?
A needle is inserted into the mother’s womb to collect amniotic fluid.
This fluid contains cells genetically identical to the foetus.
The cells are cultured, and karyotyping is done to check for chromosomal abnormalities.
If an extra chromosome 21 (Trisomy 21) is found, the foetus is diagnosed with Down syndrome.
In most cases, pregnancy is terminated if the karyotype confirms the condition.
Early diagnosis helps in making informed decisions regarding pregnancy and preparing for specialised care if the baby is born with Down syndrome.
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FAQs on What Causes Down Syndrome? Reasons, Types, Signs and Symptoms
1. Can Down Syndrome be Cured?
There is no cure for down syndrome disease. Although, the quality of life of the patient can be improved by the practice of daily essential skills such as speech, educational and physical attributes.
2. How is Down Syndrome inherited?
Generally, Down Syndrome is not inheritable. Down syndrome occurs when there is an entire extra copy of chromosome 21, or a part of it present in all the cells, or some cells. These incidents occur as random events during the formation of the reproductive cells.
3. Who is More Likely to Have a Baby with Down Syndrome?
Any woman can have a baby with Down syndrome, but the risk increases with age.
Younger mothers have a lower chance, but most babies with Down syndrome are born to them because they have more babies overall.
Risk by Age-
25 years → 1 in 1,250 chance
31 years → 1 in 1,000 chance
35 years → 1 in 400 chance
40 years → 1 in 100 chance
4. How long can a child with Down syndrome live?
Today, most children with Down syndrome live up to 60 years, and some can even reach their 80s, just like other people.
Not all individuals with Down syndrome look the same. While some may have common physical features of the condition, others may not have them at all.
5. How can you tell if a baby is unhealthy during pregnancy?
Doctors check for signs that a baby may have health problems before birth. These signs include
Unusual protein levels in the mother’s blood (higher or lower than normal).
Extra fluid behind the baby’s neck is seen in an ultrasound.
Problems in the baby’s organs, like the heart, are found during a special scan (fetal echocardiogram).
These signs help doctors detect possible birth defects early.
6. Can Folic Acid Stop Down Syndrome?
Recent Studies found that folic acid supplements may lower the risk of Down syndrome, but they cannot fully prevent it. Down syndrome happens because of an extra copy of chromosome 21, which is a genetic condition, not just a vitamin deficiency. Taking folic acid is still important for a healthy pregnancy, but it does not completely stop Down syndrome from occurring.
7. What are 5 common signs of Down syndrome?
People with Down syndrome often have these physical features
Weak muscles – Their body feels less firm, making movement slower.
Short neck with extra skin – The back of their neck may have loose skin.
Flat face and nose – Their faces look flatter than usual.
Small head, ears, and mouth – These body parts are smaller compared to others.
Upward-slanting eyes – Their eyes slant upwards, and a small skin fold may cover the inner corner.
