We all know chromosomes are large genetic storage bins in our bodies containing our DNA.

A mismatch in this chromosome number becomes the primary cause of a most common genetic disorder known as Down syndrome. And most of us are aware of this.

Do you know that there are two other causes of Down syndrome?

Yes, apart from the chromosome karyotype, there can also be two other underlying factors that might increase the possibility of Down syndrome.

How many chromosomes does a normal person have?

In common, each cell in our body has 23 pairs of chromosomes, which sums up to 46 chromosomes in each cell. One chromosome in each pair comes from the mother and the other from the father.

22 of these pairs look the same in both males and females and are called autosomes.

The 23rd pair is called the sex chromosomes and differs between each sex.

For example, a female has two copies of the XX chromosome while a male has one X and one Y chromosome.

Down Syndrome - Chromosomes Inheritance

Karyotype of Down Syndrome

The 22 pairs that are common between both genders are lined up by size. 

The karyotype of down syndrome is Trisomy 21 and is the most common chromosome condition a down syndrome baby is born with.

A karyotype is simply a complete picture of a human’s chromosomes lined up.

Something goes wrong in this chromosomal structure for a person with Down syndrome.

As a result, a baby with down syndrome gets an extra copy of chromosome 21 (Trisomy 21). This means they have one pair with three chromosomes rather than two.

This abnormal cell division resulting in an extra partial or full chromosome 21 is the main cause of Down syndrome.

Down Syndrome - trisomy

A karyotype of Down’s syndrome is denoted as 47, XY+21 (XY- male baby) or 47, XX+21 (XX – female baby).

This means that the child has a total of 47 chromosomes and one extra copy of chromosome 21.

How many Babies are affected by Down Syndrome in India?

facts about down syndrome birth in India

And there is one important point to be noted. Life expectancy with Trisomy 21 has increased exceptionally over the past few decades as medical care and social inclusion have improved.

Other factors that might increase the causes of Down Syndrome:

These are two other possibilities for Down syndrome that analysis has found.

Is Maternal and Paternal age a cause of Down Syndrome?

The highest frequency of Down syndrome was found in the maternal and paternal age group between 30 and 39 years old.

This is in comparison with parents under 30 years of age.

Down Syndrome and parent age

Can Down syndrome be inherited?

In most cases, down syndrome is not inherited. Instead, chromosomal abnormalities happen at random during the formation of the reproductive cells.

But there might be a chance of getting it inherited if a baby is affected by a type of Down Syndrome known as Translocation Down Syndrome.

To put this more precisely. This can be inherited from an unaffected parent in the case of Translocation Down Syndrome.

The parent might carry a rearrangement of genetic material between chromosome 21 and others (Balanced Translocation).

None of the genetic material is affected in a balanced translocation condition so that the parent would be normal.

But if the balanced translocation is passed from the parent to the baby, an unbalanced chromosomal condition is caused.

For example, those who inherit an unbalanced translocation of chromosome 21 may have extra genetic material from chromosome 21, which leads to Down syndrome.

What to do if your doctor suspects your unborn with a chromosomal disorder?

This condition can be first diagnosed in your 13weeks ultrasound scan (NT scan).

Please be informed that 40% of Down’s Syndrome babies do not show structural abnormalities in the scan.

These might be some other genetic disorders with severe conditions. Talk to your doctor about this.

That being said, you would be recommended some confirmatory tests if your doctor diagnoses Down syndrome conditions in your scan.

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