Background Information

A biologically normal individual has 23 pairs of chromosomes. 22 are autosomes and 1 pair consists of the sex chromosomes, which are XX in females and XY in males. In Down syndrome, a genetic condition, an individual is born with an extra copy of chromosome 21, making the total number 47 instead of the usual 46 chromosomes.

Down syndrome is associated with:

• Intellectual disability.
• Characteristic physical features.
• Developmental delays.

It is named after John Down, a British physician who first gave a full description of  the condition in 1866. Earlier descriptions were given by Dominique Esquirol and Edouard Seguin, French psychiatrist and physician respectively.

Current Trends & Data

• It is the most common chromosome-related disorder in the United States of America.
• It is estimated that 1 in 7 babies in the US  and 1 in 1,000 babies globally are born with this condition.
• Almost 200,000 persons live with this condition in the US.

 

Potential Risks

Age. The incidence of Down syndrome increases with maternal age. Women aged 35 years and above are more likely to give birth to children with Down syndrome or any other genetic condition.

 

 Factors That Contribute

Down syndrome is caused by presence of extra chromosome 21.

 

Types

The three types of Down syndrome are:

•  Trisomy 21.
• Translocation.
• Mosaicism.

These types have different causes.

 

Trisomy 21. it accounts for almost 95% of all Down syndrome cases, becoming the most commmon form. In trisomy, each cell has  three copies of chromosome 21 instead of the usual two copies. It occurs during fetal development. It is caused by an error referred to as non-disjunction which can occur during cell division.

Translocation. It accounts for less than 4% of Down syndrome cases. It occurs when there is partial or complete amount of chromosome 21 attached to another chromosome. In translocation, chromosome 21 is not separate but it gets relocated to another numbered chromosome.

Mosaicism. Mosaic Down syndrome is the accounts for less than 1% of all cases, making it the rarest form. It happens when some cells carry 46 chromosomes while others have 47.

 

Manifestations & Indicators

 

Physical signs and symptoms:

1. Flat nose bridge.
2. Short neck.
3. Shorter height.
4. Excessive flexibility.
5. Palmar crease.
6. Small pinky fingers that point inward towards the thumb.
7. Weak muscle tone at birth.
8. Slanted eyelids that point upward (palpebral fissures).
9. Protruding tongue.

 

During child growth, there can be additional signs and symptoms;

1. Obstructive sleep apnea.
2. Congenital heart disease.
3. Loss of hearing.

 

Behavioral signs and symptoms:

1. Stubbornness.
2. Difficulty concentrating.
3. Obesssive or compulsive habits.

 

Cognitive signs and symptoms:

1. Language is delayed.
2. Short-term and long-term  memories are affected.

 

 Evaluation Techniques

Prenatal screening tests. They show the chances that a woman is carrying in her womb a fetus with Down syndrome. They do not confirm a diagnosis. An example of screening tests is ultrasound.

Diagnostic tests. They are used to diagnose Down syndrome in a baby. During pregnancy, tests that can be conducted to identify this syndrome are:

1.  Chorionic villus sampling (CVS).
2.  Amniocentesis.
3. Percutaneous umbilical cord sampling.

Karyotyping.  This can be performed as a post-natal test to check for extra chromosome 21 and confirm a Down syndrome diagnosis.

 

 Approaches to Treatment & Care

• Down syndrome does not have a cure.
• However, there are various treatment strategies that can be employed to help affected children. These are:

1. Physical or occupational therapy.
2. Speech therapy.
3. Treatment of underlying medical conditions.

 

• Depending on the child’s particular needs, the team of experts may include:

1. Paediatric cardiologist.
2. Paediatric ear, nose and throat (ENT) specialist.
3. Speech pathologist.
4. Ophthalmologist.
5. Physical therapist.
6. Occupational therapist.

 

 Differential Diagnosis

• Congenital hypothyroidism.
• Trisomy 18.
• Zellweger syndrome.

 

 Possible Consequences

The following are complications  associated with Down syndrome:

• Heart defects.
• Gastrointestinal Problems such as duodenal atresia.
• Vision problems such as eye cataracts.
• Loss of hearing.

 

Preventive Measures

• Down syndrome is a genetic condition.
• To prevent chances of conceiving a child with Down syndrome, genetic testing should be performed and counselling done to couples who are planning to conceive.