What is Down Syndrome?


What is Down syndrome?

In every cell in the human body there is a nucleus, where genetic material is stored in genes. Genes carry the codes responsible for all of our inherited traits and are grouped along rod-like structures called chromosomes. Typically, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21.

This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome. A few of the common physical traits of Down syndrome are low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the center of the palm – although each person with Down syndrome is a unique individual and may possess these characteristics to different degrees, or not at all.

People with Down syndrome experience cognitive delays, but the effect is usually mild to moderate and is not indicative of the many strengths and talents that each individual possesses. Children with Down syndrome learn to sit, walk, talk, play, and do most other activities; only somewhat later than their peers without Down syndrome.

What causes Down syndrome?

Down syndrome is usually caused by an error in cell division called nondisjunction. It is not known why this occurs. However, it is known that the error occurs at conception and is not related to anything the mother did during pregnancy. It has been known for some time that the incidence of Down syndrome increases with advancing maternal age. However, 80% of children with Down syndrome are born to women under 35 years of age.

How common is Down syndrome?

According to the World Health Organization, out of every 1000 babies born around the world, 1 will have Down syndrome. Down syndrome affects people of all ages, races, religious and economic situations. It can happen to anyone, although women over the age of 35 have a higher risk of having babies with Down syndrome.

When was Down syndrome discovered?

In 1866, well before the genetic link to Down syndrome was established, John Langdon Down, an English physician, described the condition as a distinct set of characteristics. He noted the common features associated with Down syndrome such as straight, thin hair, a small nose, and a broad face. Down syndrome is thus named for the man credited with first describing it.

In the twentieth century, advances in genetic research helped scientists begin to understand the cause of Down syndrome. By the early 1930s, some researchers began to suspect that Down syndrome might be caused by a chromosomal abnormality. In 1959, Jerome Lejune, a French geneticist, discovered that cells grown from individuals with Down syndrome had an extra chromosome. Later, researchers determined that the extra chromosome was the twenty-first. These findings led to the discovery of other forms of Down syndrome, including translocation and mosaicism.

What are the different types of Down syndrome?

Down syndrome (or Trisomy 21)

accounts for ninety-five percent of people with Down syndrome. A child with Trisomy 21 has three copies of chromosome 21, rather than the normal pair.

Translocation Down syndrome

accounts for just three to four percent of people with Down syndrome. Translocation is what people are referring to if they say that the condition is inherited, because usually one parent is a carrier. The extra #21 chromosome is present, but attached to a different chromosome in the egg or sperm. The clinical features of people with Translocation Down syndrome are indistinguishable from those with Trisomy 21.

Mosaic Down syndrome

accounts for less than one percent of all people with Down syndrome. Children born with Mosaic Down syndrome have some cells with three copies of chromosome 21 and some cells that have the usual pair. Clinically, babies born with Mosaic Down syndrome can have the same features and health problems seen in babies born with Trisomy 21 or Translocation Down syndrome. However, the presence of cells with the normal number of chromosomes may result in fewer characteristics of Down syndrome.

How is Down syndrome diagnosed?

Down syndrome can be detected during pregnancy through various prenatal tests. Down syndrome can also be diagnosed after birth with a chromosomal analysis called a karyotype.


The two types of prenatal tests used to detect Down syndrome are called screening tests and diagnostic tests.

Screening tests determine what the chances are that your baby will be born with Down syndrome or other medical conditions. This kind of testing does not definitively diagnose a fetus with one of these conditions.

The different types of screening tests include blood tests, which are used to measure protein and hormone levelsin pregnant women. Abnormally increased or decreased levels can indicate a genetic condition. New blood tests can also detect chromosomal material from the fetus that is circulating in the mother’s blood. Another screening test is an ultrasound, which is a non-invasive imagining technique that uses sound waves to generate an image of the fetus. An ultrasound can identify congenital heart conditions and other structural changes that may indicate a diagnosis of Down syndrome. The combined results of these two tests are used to estimate the chance that your baby will be born with Down syndrome.

Diagnostic tests can determine whether or not your fetus has Down syndrome with nearly 100 percent accuracy. However, because these tests are performed inside the uterus, they carry a small increased risk of miscarriage and other complications.

The different types of diagnostic testing include Chorionic villus sampling (CVS), a prenatal diagnosis method in which a small biopsy of the placenta is taken for specific genetic testing. CVS is used to detect any condition that involves specific chromosomal abnormalities, like Down syndrome. This test is usually performed during the first trimester between 10-14 weeks of gestation. Amniocentesis is a prenatal diagnosis method in which a needle is inserted into the amniotic sac that surrounds the baby. Amniocentesis is most often used to detect Down syndrome and other chromosomal abnormalities. This test is usually done in the second trimester, after 15 weeks of gestation.

At Birth

Down syndrome can also be diagnosed after the baby is born. Since Down syndrome involves a set of unique characteristics, a doctor can usually tell whether a baby should be tested based on a physical examination. To confirm the findings, a karyotype (a small blood or tissue sample) can be analyzed to determine the presence of extra material from chromosome 21. This information is important in determining the chance of a mother having a baby with the condition in the future.

What impact does Down syndrome have on society?

In many countries around the world, individuals with Down syndrome are becoming increasingly integrated into society and community organizations, such as school, health care systems, work forces, and social and recreational activities. Adults with Down syndrome can take care of themselves, hold jobs, and enjoy activities with family and friends.

It is important to remember that while children and adults with Down syndrome experience developmental delays, they also have many talents and gifts and should be given the opportunity and encouragement to develop them.

Most children with Down syndrome have mild to moderate impairments but it is important to note that they are more like other children than they are different. Early Intervention services should be provided shortly after birth. These services should include physical, speech and developmental therapies.

Due to advances in medical technology, individuals with Down syndrome are living longer than ever before. In 1910, children with Down syndrome were expected to survive to age nine. Now, with recent advancements in clinical treatment, most particularly corrective heart surgeries, as many as 80% of adults with Down syndrome reach age 60, and many live even longer. This means that more and more people are interacting with individuals with Down syndrome, increasing the need for widespread public education and acceptance. This applies even more so in Pakistan, where the issue of physical and intellectual disabilities is largely taboo.