What is Down Syndrome?

Down syndrome is a genetic disorder caused by the presence of an extra copy of chromosome 21. This condition, also known as Trisomy 21, leads to developmental and physical differences. It is one of the most common chromosomal abnormalities and occurs in about 1 in every 700 births worldwide.

Causes

Typically, a person has 46 chromosomes, arranged in 23 pairs. Down syndrome occurs when there is an extra full or partial copy of chromosome 21. This extra genetic material affects development in several ways. The most common cause is nondisjunction, where chromosomes fail to separate properly during the formation of the egg or sperm, resulting in an embryo with three copies of chromosome 21.

Types of Down Syndrome

Trisomy 21: About 95% of people with Down syndrome have Trisomy 21, in which every cell in the body has three copies of chromosome 21 instead of two.

Translocation Down Syndrome: In about 3-4% of cases, a part of chromosome 21 becomes attached (translocated) to another chromosome before or at conception. These individuals have two copies of chromosome 21, but they also have extra genetic material from chromosome 21 attached to another chromosome.

Mosaic Down Syndrome: A rare form where only some cells have an extra copy of chromosome 21, while others have the typical two copies. This results in a milder presentation of the condition.

Characteristics

People with Down syndrome may exhibit a variety of characteristics, though not all individuals will have the same traits. Common physical features include:

A flat facial profile, especially around the nose

Upward slanting eyes, often with a skin fold covering the inner corner

A small head and ears

A short neck

A single deep crease across the center of the palm (simian crease)

Poor muscle tone (hypotonia) and loose joints

Cognitive and Developmental Impact

Intellectual Disability: Most individuals with Down syndrome have mild to moderate intellectual disability, with an IQ that tends to range from 50 to 70. They may experience delays in speech, language, and motor skills.

Developmental Delays: There may be delays in reaching developmental milestones such as sitting, walking, or speaking, but individuals with Down syndrome can still lead fulfilling lives with the right support.

Health Complications

Individuals with Down syndrome are at a higher risk of certain health issues, including:

Heart defects: About 50% of babies with Down syndrome are born with congenital heart defects.

Respiratory and hearing problems: These include frequent ear infections and potential hearing loss.

Vision problems: Many may have conditions such as cataracts or other vision issues.

Thyroid disorders: Hypothyroidism is more common in people with Down syndrome.

Sleep apnea: Due to anatomical differences, many individuals with Down syndrome experience obstructive sleep apnea.

Leukemia: Children with Down syndrome are at increased risk of certain types of leukemia.

Life Expectancy and Quality of Life

Advancements in healthcare have significantly improved the life expectancy for people with Down syndrome. Many individuals now live into their 60s. Early interventions, therapies, and support systems help enhance cognitive and physical development, allowing many people with Down syndrome to go to school, work, and participate in social and recreational activities.

Prenatal Diagnosis

Down syndrome can be diagnosed during pregnancy through screening tests like:

Ultrasound and blood tests: These can indicate a higher risk of Down syndrome.

Diagnostic tests: These include amniocentesis or chorionic villus sampling (CVS), which can confirm the presence of the extra chromosome 21.

Social Inclusion

With increasing awareness and advocacy, society is becoming more inclusive of individuals with Down syndrome, with emphasis on education, employment opportunities, and community involvement.

In summary, Down syndrome is a genetic condition resulting from an extra copy of chromosome 21, leading to a variety of developmental, intellectual, and physical traits. While it presents challenges, individuals with Down syndrome can live fulfilling and meaningful lives.