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What do you know about World Down Syndrome Day?
Down syndrome is a condition in which a child inherits extra genetic material from his or her parents

What do you know about World Down Syndrome Day?

Tuesday, March 21, 2023 marked the 18th anniversary of World Down Syndrome Day. The selection of March, the third month of the year and the 21st day, is to honour the uniqueness of the underlying genetic anomaly of people with Down syndrome who have three copies of the 21st chromosome.

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Down syndrome

Among other things, the day raises awareness of what Down syndrome is, what it means to have Down syndrome, and how people with Down syndrome can play vital roles in our lives and communities.

The theme for this year is “With Us Not For Us” which emphasises the fact that people with disabilities have the right to be treated fairly and have the same opportunities as everyone else, working with others to improve their lives.

You might also have noticed people wearing different socks colours which draws attention to the basic problem in Down syndrome- the chromosomes which are shaped like a sock.

Down syndrome is a condition in which a child inherits extra genetic material from his/her parents. This inheritance results in delays in the way the child develops, both intellectually and physically.

The disease is named after Dr John Langdon Down who first described it in 1887. Its frequency of occurrence is estimated to be one in every 800 babies.

The reason why Down syndrome occurs is exactly not known but we know that it results from an error in the way vehicles of inheritance called chromosomes arrange themselves.

Although any woman can give birth to a child with Down syndrome, women aged 35 years and above have a significantly increased risk of having a child with the condition.

Normally, at the time of conception, a baby inherits genetic information from their parents. These genetic material numbers 46: 23 from the mother and 23 from the father.

Chromosome 21 

In most cases of Down syndrome, a child gets an extra copy of the genetic material either in whole or in part located on number 21 of the genetic material or chromosome 21 — making a total of 47 instead of 46 chromosomes.
 

It is this extra genetic material that causes the physical features and developmental delays seen in children with Down syndrome.

By the time a female child is born, the eggs in her ovary are in a certain stage of cell division where the chromosome materials called chromatids are in a mesh-like network making direct contact with each other.

They continue to remain in contact with each other as the child grows all the way to ovulation where that particular egg quickly divides to form a mature egg and another immature one called a polar body. Because these chromatids have been in contact with each other for so long, they form strong bonds with each other such that separating them becomes difficult during cell division.

The more advanced in years the woman is during ovulation, the longer the period that the chromatids have been in contact with each other, and the more difficult the separation.

Thus, an extra copy of the chromosome is pulled by the other. This process is called non-disjunction and is mostly seen in women older than 35 years of age with children with Down syndrome.

With nondisjunction, a sperm or egg cell is produced with an extra copy of chromosome 21; the gamete thus has 24 chromosomes instead of 23. When combined with a normal gamete from the other parent, the embryo now has 47 chromosomes, with three copies of chromosome 21. In this type, all the cells in the body have extra copy of chromosome 21. Sometimes some of the cells in the body have normal 23 copies of chromosomes and other cells have extra copies 21, this is called Mosaicism and they exhibit milder features of the condition.

Another way of getting extra genetic materials on chromosome 21 is a form called translocation. In this case, the long arm of chromosome 21 becomes attached to another chromosome, often chromosome number 14. Thus, extra genetic material on chromosome 21 becomes attached to another chromosome.

Down syndrome arising from translocation is often referred to as familial Down syndrome. It does not show the maternal age effect and can be seen in younger mothers and the extra genetic material is just as likely to have come from fathers as mothers.

Flat facial profile

Rarely, a region on chromosome 21 will undergo a duplication event leading to extra copies of some, but not all, of the genes on chromosome 21. If the duplicated region has genes that are responsible for Down syndrome physical and mental characteristics, such resultant babies or individuals will show those characteristics.

The physical features and medical problems associated with Down syndrome can vary widely among individuals. Some people with the condition can lead a normal life while others need a lot of medical attention and support.
Common physical features include flat facial profile, an upward slant to the eyes, widened space between the eyes, small and low set ears and a protruding tongue.

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Other features are short stubby fingers, single crease in the palms and a wide gap between the first and second toes. At birth, children with Down syndrome are usually of average size, but they tend to grow at a slower rate and remain smaller than their peers.

For infants, low muscle tone may contribute to sucking and feeding problems as well as floppy appearance. They also have constipation and other digestive issues. Toddlers and older children may have delays in speech and self-care skills like feeding, dressing and toilet training. One of the constant features in Down syndrome is delayed developments.

Down syndrome affects the person’s ability to learn in different ways, but most have mild to moderate intellectual impairment. However, children with the condition can and do learn, and are capable of developing skills throughout their lives. They simply reach their goals at a different pace — which is why it is important to avoid comparing a child with Down syndrome to another sibling or even other children with the condition because they always have intellectual disabilities though to varying degrees.
 
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A member of Paediatric Society of Ghana

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