Down Syndrome – a Genetic Disorder

Down Syndrome – Introduction

According to the National Association for Down syndrome (2004), Down syndrome is a "genetic condition that causes delays in physical and intellectual development."

Also known as Trisomy 21, it is one of the most common genetic disorders that occur at childbirth. It is a condition in which a patient has 3 copies of chromosome 21 rather than 2. This extra or added genetic material causes delay in development of a child by changing the finely tuned balance of the body that leads to retardation. Down syndrome is usually identified at birth or shortly afterwards.

This pediatric disorder is named after John Langdon Down, the British doctor who identified it in 1866.

Causes of Down Syndrome

Down syndrome is usually caused by an error in cell division called nondisjunction. Every normal person has 46 chromosomes. However, if there is an extra chromosome 21, it may cause Down syndrome.

This mix up of cells causes problems such as mental retardation and slow physical development. 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. In some cases, it has been related to the age of the mother. However, according to statistics, 80% of the children with Down syndrome are born to mothers under 35 years of age.

Types of Down Syndrome

There are 3 different types of Down syndrome:

Regular Trisomy 21

In this type of Down syndrome, all the cells have an extra chromosome 21. Around 94% of people with Down's syndrome are found to have this type.

Translocation

The extra chromosome 21 material is attached to another chromosome and one of the parent's may carry the translocated chromosome without any signs of this condition themselves. This accounts for around 4% of the cases.

Mosaic

Only some of the cells have this extra chromosome 21. Around 2% of people with Down syndrome have this type, which result in milder features.

Symptoms of Down Syndrome

• Decreased or low muscle tone at birth
• Separated sutures (joints between the bones of the skull)
• Asymmetrical or odd-shaped skull
• Round head with flat area at the back of the head (occiput)
• Small skull (microcephaly)
• Upward slanting eyes, unusual for ethnic group
• Small mouth with protruding or enlarged tongue (see tongue problems)
• Small ears
• Broad short hands
• Single crease on the palm
• Retarded growth and development
• Delayed mental and social skills (mental retardation)
• Iris lesion (an abnormality of the colored part of the eye called Brushfield spots)
• Delays in speech and self-care skills like feeding, dressing and toilet teaching in toddlers
• Problems in sucking and feeding and other digestive issues

Down Syndrome Effects

Individuals with Down syndrome have a lower than average cognitive ability and mild to moderate mental retardation. A small number of people also have severe to profound mental retardation. Developmental disabilities often manifest as a tendency towards concrete thinking or naïveté.

Children and adults with Down syndrome experience slow developments in their physical abilities too. However, this does not mean that they are disabled. Instead these individuals may have talents and skills though they take a long time to be developed.

Diagnosis and Tests of Down Syndrome

Down syndrome can be identified at birth by observing the typical physical abnormalities associated with the disorder. However, these physical abnormalities need to be confirmed through chromosome tests called the karyotype that provides a visual display of the chromosomes.

Down syndrome can also be detected before birth through tests. For this reason pre-natal diagnosis of the child is imperative. There are 2 types of procedures for diagnosis of pregnant women - screening tests and diagnostic tests.

Screening Tests

Screening tests involve the estimation of risk of the baby having Down syndrome.

• The most commonly used screening test is “The Triple Screen.” It is combination of three tests that measure quantities of various substances in the blood. These tests are usually done between 15 and 20 weeks of gestation.
• Sonograms (ultrasounds) are usually performed in conjunction with other screenings. They can show some physical traits that help in calculating the risk of Down syndrome.

Screening tests do not accurately confirm the diagnosis of Down syndrome. In fact, false positives and false negatives frequently occur.

Diagnostic Tests

Three diagnostic tests are currently available:

• Amniocentesis - performed between 12 and 20 weeks gestation.
• Chorionic Villus Sampling (CVS) - conducted between 8 and 12 weeks.
• Percutaneous Umbilical Blood Sampling (PUBS) - performed after 20 weeks.

However, the triple screen test does not actually guarantee that the baby does not have Down syndrome. Another negative impact includes miscarriage due to which doctors discourage pre-natal tests.

Treatment for Down Syndrome

Unfortunately, there is no specific treatment or cure for Down syndrome. Early intervention can help in rectifying the physical limitation and develop the growth process of people suffering from this disorder through therapies and special care.

Children should go to special education schools so that their needs and requirements for specialized programs are met. More importantly as these children grow, they should be encouraged to participate in secondary and college education as others.

Also, if other problems accompanying this disorder are dealt with, such as heart defects, hearing loss and visual problems and increased immunity, the patients’ quality of life can be improved. With proper medical care, most of the children suffering from Down syndrome can be helped in leading normal and healthy lives.