What is Down syndrome?

1. What is Down syndrome?

There are three different causes of Down syndrome:

Trisomy 21

Every cell in the body comes from one initial cell: The fertilized egg, which is called a zygote. After fertilization, the zygote then proceeds to divide.  As new cells form, the chromosomes, duplicate themselves so that the resulting cells have the same number of chromosomes as the original cell. A chromosome is a thread like structure of DNA (nucleic acids and proteins) that carry genes. The term “trisomy is used to describe the presence of an extra chromosome- or three instead of the usual pair. Trisomy 21 occurs when there is an extra 21stchromosome.

Translocation Down syndrome

People with Translocation Down syndrome can inherit the condition from an unaffected parent.  The parent carries a rearrangement of genetic material between chromosome 21 and another chromosome. This rearrangement is called a balanced translocation. No genetic material is gained or lost in a balanced translocation, so these chromosomal changes usually do not cause any health problems. However, as this translocation is passed to the next generation, it can become unbalanced. People who inherit an unbalanced translocation involving chromosome 21 may have extra genetic material from chromosome 21, which causes Down syndrome. With Translocation the 21st chromosome becomes attached (Trans-located) onto another chromosome, before or at conception. People with this type of Down syndrome have the usual two copies of their 21st chromosome, but they also have additional material from the 21st chromosome attached to another pair of chromosomes.

Mosaic Down syndrome

People who have Mosaic Down syndrome have some chromosomes that contain the extra chromosome and some that contain the typical two. Clinically, babies born with Mosaic Down syndrome have some of the same features and health problems seen in babies with Trisomy 21 and translocation Down syndrome. However, the presence of the cells that don’t contain the extra chromosome may result in fewer characteristics of Down syndrome.

Typical Chromosome Trisomy 21 Chromosome

2. What physical characteristics are associated with Down syndrome?


The additional genetic material (extra 21st Chromosome) alters the course of development and causes some of the following characteristics;

  • Hypotonic is a state of low muscle tone (the amount of tension or resistance to stretch in a muscle), often involving reduced muscle strength.
  • Flat facial features, with a small nose
  • Upward slant to the eyes
  • Small skin folds on the inner corner of the eyes
  • Small ears
  • Single deep crease across the center of the palm
  • Hyper flexibility (excessive ability to extend joints)
  • Fifth finger has only one flexion furrow instead of two
  • Extra space between the big toe and the second toe
  • Enlarged tongue that tends to stick out
  • Physical development is often slower than typical. Most children with Down syndrome never reach their average adult height.

Not everyone with Down syndrome will inherit all of these characteristics.

Life expectancy for people with Down syndrome has increased dramatically in recent decades – from 25 in 1983 to 60 today.

3. What are the incidences of Down syndrome?


It occurs once in every 691 live births. 95% Trisomy 21, 4%Translocation, 1% Mosaic.

More than 400,000 people in the U.S. have this genetic condition.

80% of babies with Down syndrome are born to mothers under the age of 35.

4. Are there any differences in life expectancy?

Life expectancy for people with Down syndrome has increased dramatically in recent decades – from 25 in 1983 to 60 today.

5. What type of life style does a person with Down syndrome have?

Down syndrome is a lifelong condition. Services early in life will often help babies and children with Down syndrome to improve their physical and intellectual abilities. Most of these services focus on helping children with Down syndrome develop to their full potential. These services include speech, occupational, and physical therapy, and they are typically offered through early intervention programs in each state. Children with Down syndrome may also need extra help or attention in school, although many children are included in regular classes.

Many people with Down Syndrome lead productive and fulfilling lives well into adulthood. They can have jobs and live independently. However, it is important for people with Down Syndrome to be involved in their community, take good care of themselves, and see a healthcare provider regularly. Families of people with Down syndrome often can help their loved ones by connecting with other families that have had children with Down syndrome. This may help families gain insight into overcoming potential differences in caring for their child with Down syndrome.