Down syndrome (DS) is a genetic disorder that occurs when there is an abnormal cell division, which results in an extra copy of chromosome 21. This extra genetic material is the cause of some developmental changes and physical features of DS.
A baby is typically born with 46 chromosomes, but in babies with Down syndrome, there is an extra copy of the chromosome, chromosome 21. This extra chromosome changes the baby’s body and brain development, which can cause mental and physical challenges for the baby.
People with Down syndrome usually look alike. But despite the similarities in facial appearances, each person has different abilities. They usually have low IQ and are slower to speak than other children.
Symptoms of Down syndrome
Down syndrome may be mild, moderate or severe. Some patients are healthy while others may have significant health challenges such as heart defects. Some of the common features of DS include:
- Small head
- Short neck
- Protruding tongue
- Small ears
- Poor muscle tone
- Small hands and feet
- A single line across the palm of the hand
- Shorter height as children and adults
Types of Down syndrome
There are three types of Down syndrome; nevertheless, without diagnosis it is hard to spot one type from another, because, the physical features remain the same.
In this type, which is about 96%, each cell in the body has 3 separate copies of chromosome 21 instead of the normal 2 copies.
Translocation Down syndrome
This can occur when a portion of chromosome 21 becomes translocated onto another chromosome, before or at conception. The child would have the two copies of chromosome 21 and yet another copy of genetic material from chromosome 21 attached to another chromosome.
Translocation Down syndrome accounts for a small percentage of people with DS.
Mosaic Down syndrome
This is a rare form of Down syndrome. In Mosaic DS the child or children have 3 copies of chromosome 21 in some cells and 2 copies in normal cells. They may have fewer features of the condition due to the presence of some normal cells with normal 2 copies of chromosome 21.
Is Down syndrome inherited?
Down syndrome actually occurs due to a mistake in cell division during early development of the fetus. However, translocation DS can be passed from parent to child. Nevertheless, only a small percentage of children with translocation DS inherited it from one of their parents.
In this case, one of the parents has some rearranged genetic material from chromosome 21 with no extra genetic material. He or she has no symptoms of DS, but can pass an unbalanced translocation to the child that will result in Down syndrome.
Causes and risk factors
The main cause of DS is the extra genetic material of chromosome 21, which leads to the physical features and developmental challenges that is seen among people with DS.
Some of the risk factors are:
The older a woman becomes, the greater the chances of having a child or children with Down syndrome. Women who are 35 years or older are at high risk of having their fetus affected by DS than women who become pregnant at their younger age.
Being carriers of genetic translocation for Down syndrome
As indicated above, both parents can pass the genetic translocation for Down syndrome on to their children.
Complications associated with Down syndrome
Heart defects: About half of the children with DS have some heart defects, which may be life threatening and may require surgical operations in early infancy.
Dementia: people with Down syndrome are at greater risk of dementia at older age, say 50 and above. Having DS also increases the chances of developing Alzheimer’s disease.
Leukemia: The children have increased risk of leukemia. Other complications include:
- Spinal problem
- Underactive thyroid
Life Expectancy of people with Down syndrome
Unlike in previous ages, life expectancy for people living with DS has dramatically increased. Some people can live for more than 60 years, depending on the severity of health complications.
There is no cure for people with DS; but some services can be offered to such people that can improve their physical and intellectual capabilities. These services include speech, occupational and physical therapy.