Down Syndrome
Down Syndrome is a genetic condition caused by the presence of an extra copy of chromosome 21. This additional chromosome impacts physical growth, cognitive abilities, and development, leading to a range of unique characteristics and health issues. Down Syndrome is not an illness but a lifelong condition that affects individuals differently, with varying levels of independence and capability.
Key Features of Down Syndrome
Physical Characteristics
Distinctive facial features, including a flattened face, almond-shaped eyes that slant upward, a short neck, and a small mouth and nose.
Low muscle tone and loose joints, which may affect physical development and coordination.
Shorter stature, with smaller hands and feet compared to peers.
Cognitive and Developmental Impact
Mild to moderate intellectual disability, impacting learning and problem-solving abilities.
Speech and language delays, with potential difficulties in clear articulation and understanding complex language.
Delayed motor skills development, including sitting, walking, and fine motor tasks.
Health Concerns
Increased risk of certain medical issues, including congenital heart defects, respiratory issues, and hearing and vision problems.
Higher susceptibility to thyroid conditions, digestive issues, and immune system irregularities.
Behavioral and Social Strengths
Often exhibit positive social engagement, friendliness, and warmth in interactions.
Ability to learn, develop skills, and lead fulfilling lives with the appropriate support and resources.
Signs and Symptoms
Down Syndrome is typically identified by a combination of physical, cognitive, and developmental signs. These characteristics can vary from person to person, with each individual displaying unique strengths and challenges.
Physical Signs
- Distinct Facial Features: Flattened facial profile, upward slanting eyes, small ears, and a short neck.
- Hands and Feet: Small hands and feet, with a single crease across the palm (palmar crease).
- Muscle Tone: Low muscle tone (hypotonia), leading to a “floppy” appearance in infants, and flexible or loose joints.
Cognitive and Developmental Signs
- Intellectual Disability: Ranges from mild to moderate, impacting reasoning, learning speed, and memory.
- Delayed Milestones: Slower progression in sitting, walking, and other motor skills, as well as speech and language delays.
- Attention and Focus: Shorter attention span, impulsive behavior, and potential difficulty in focusing on tasks for long periods.
Health-Related Signs
- Heart Defects: Congenital heart conditions are common in children with Down Syndrome, affecting their physical endurance and energy levels.
- Vision and Hearing Issues: Increased likelihood of hearing loss, vision challenges, and other sensory processing issues.
- Thyroid and Immune Concerns: Higher risk for thyroid problems, respiratory infections, and other immune-related issues.
Behavioral and Social Traits
- Social Engagement: Many individuals with Down Syndrome are known for their sociability, warmth, and positive social interactions.
- Emotional Awareness: Often display strong empathy, sensitivity to others’ emotions, and a genuine interest in socializing and bonding with family and friends.
Causes
Primary Cause
Trisomy 21: In about 95% of cases, Down Syndrome is caused by Trisomy 21, where each cell in the body has three copies of chromosome 21 instead of two.
Mosaic Down Syndrome: In rare cases, some cells have the usual two copies of chromosome 21, while others have three, leading to a “mosaic” pattern.
Translocation Down Syndrome: About 4% of cases result from part of chromosome 21 attaching to another chromosome, often chromosome 14, leading to an extra chromosome.
Risk Factors
Risk Factors
Maternal Age: The most significant risk factor is the age of the mother at the time of conception. The risk of having a child with Down Syndrome increases significantly for mothers over 35, with the risk continuing to rise as maternal age increases.
Genetic Predisposition: While not inherited in most cases, in the rare case of Translocation Down Syndrome, there may be a hereditary component. If one parent carries a translocated chromosome, they may have a higher chance of passing it on to their child.
Previous Child with Down Syndrome: Parents who have had one child with Down Syndrome have an increased, though still low, chance of having another child with the condition.
Environmental Factors: There is no direct evidence linking environmental factors like diet or lifestyle to an increased risk of Down Syndrome. However, general prenatal health and avoiding harmful substances can support a healthy pregnancy overall.
Diagnosis of Down Syndrome
Down Syndrome can be diagnosed both prenatally (before birth) and postnatally (after birth) using a variety of screening and diagnostic tests. Early diagnosis allows parents and healthcare providers to plan appropriate support and care for the child.
1. Prenatal Screening Tests
Screening tests during pregnancy estimate the likelihood that a baby may have Down Syndrome, but they do not provide a definitive diagnosis. These non-invasive tests are typically offered in the first and second trimesters of pregnancy.
First Trimester Screening:
Nuchal Translucency Ultrasound: Measures the fluid at the back of the fetus’s neck. A higher level of fluid can indicate a higher risk of Down Syndrome.
Blood Tests: Measures levels of certain proteins and hormones in the mother’s blood that may indicate chromosomal abnormalities.
Second Trimester Screening:
Quad Screen: Measures four specific substances in the mother’s blood. Results help estimate the likelihood of Down Syndrome.
Cell-Free DNA Test (cfDNA): Analyzes fetal DNA in the mother’s blood for chromosomal conditions like Down Syndrome. It can be done as early as 10 weeks of pregnancy and is highly accurate.
2. Diagnostic Tests (Prenatal)
Diagnostic tests are typically more definitive but are invasive. They are recommended when screening results suggest a high risk or for mothers over age 35. These tests involve some risk to the fetus, so they are generally only done after a positive screening test.
Chorionic Villus Sampling (CVS): Conducted between 10 and 13 weeks, CVS examines placental tissue to confirm if there’s an extra chromosome 21.
Amniocentesis: Performed between 15 and 20 weeks, amniocentesis examines amniotic fluid for chromosomal abnormalities with a high degree of accuracy.
3. Postnatal Diagnosis
After birth, Down Syndrome is typically identified based on physical characteristics, followed by a confirmatory genetic test.
Physical Examination: A doctor may initially identify Down Syndrome by observing physical signs, such as facial features, muscle tone, and joint flexibility.
Karyotype Test: A blood sample is taken to examine the baby’s chromosomes under a microscope. This test confirms the presence of an extra chromosome 21.
