Types of Down Syndrome
Down syndrome, also known as trisomy 21, is a genetic disorder that results in developmental and physical delays. It is named after Dr. John Langdon Down who first described the condition in 1866. Down syndrome is caused by the presence of an extra chromosome in a person's DNA, resulting in a total of 47 chromosomes instead of 46. This extra chromosome leads to physical and intellectual disabilities that can range in severity. For individuals and families affected by this condition, accessing Down syndrome support services can provide essential assistance and resources.
The three most common types of Down Syndrome are as follows:
The most common and well-known form of Down syndrome is Trisomy 21, which occurs when a person has three copies of chromosome 21 instead of two. This form of Down syndrome accounts for approximately 95% of all cases. Trisomy 21 occurs randomly and is not caused by any environmental factors or behaviours.
In trisomy 21, the extra chromosome results in an overproduction of certain proteins that are critical for normal development. This leads to the physical and intellectual delays that are common in individuals with Down syndrome. Trisomy 21 is caused by a non-disjunction event, where the chromosomes do not separate properly during cell division. As a result, the extra chromosome is present in every cell of the body, leading to the physical and intellectual delays that are seen in individuals with Down syndrome.
Translocation Down Syndrome
Another form of Down syndrome is known as translocation Down syndrome, which accounts for approximately 4% of all cases. In this form of Down syndrome, a portion of chromosome 21 breaks off and attaches to another chromosome. The person with translocation Down syndrome still has the typical 47 chromosomes, but the extra genetic material from chromosome 21 results in physical and intellectual delays. Unlike trisomy 21, translocation Down syndrome is not always inherited and can occur spontaneously.
Mosaic Down Syndrome
A rarer form of Down syndrome is known as mosaic Down syndrome, which occurs when some cells have the typical 46 chromosomes and others have 47 chromosomes. This form of Down syndrome is caused by a non-disjunction event that occurs later in development, resulting in some cells with the extra chromosome and others without. Mosaic Down syndrome is rare, accounting for only 1% of all cases of Down syndrome. The severity of physical and intellectual delays can vary depending on the number of cells with the extra chromosome.
How Genetics Affect Down Syndrome
The exact cause of Down syndrome is not known, but it is believed to be a combination of genetic and environmental factors. The likelihood of having a child with Down syndrome increases as the mother's age increases, with the greatest risk being for women over the age of 35. However, it is important to note that the vast majority of children with Down syndrome are born to women under the age of 35. Down syndrome is not caused by anything the mother or father did or did not do, and it is not a result of any behavioural or environmental factors.
Down Syndrome Symptoms
The symptoms of Down syndrome can vary in severity and can range from physical and intellectual delays to characteristic facial features and health problems. Some common physical symptoms of Down syndrome include a small head, a flat face, and a short neck. Individuals with Down syndrome may also have intellectual delays, including a lower IQ, developmental delays, and difficulties with learning and problem-solving. They may also have difficulty with fine motor skills, such as writing and holding objects, as well as gross motor skills, such as walking and running.
- Physical Characteristics: Low muscle tone, short stature, a flat facial profile, an upward slant to the eyes, a single deep crease across the centre of the palm, and small hands and feet.
- Developmental Delays: Delays in speech and language development, as well as cognitive and motor skill delays, are common in people with Down syndrome.
- Intellectual Disability: Down syndrome is associated with mild to moderate intellectual disability, which affects a person’s ability to think, reason, and learn.
- Congenital Heart Defects: Approximately 50% of babies with Down syndrome are born with a congenital heart defect, which can range from mild to severe.
- Hearing and Vision Impairments: Hearing and vision impairments are common in people with Down syndrome, and they may also have difficulties with spatial awareness and coordination.
- Alzheimer’s Disease: People with Down syndrome have an increased risk of developing Alzheimer’s disease as they age.
- Thyroid Issues: People with Down syndrome have an increased risk of developing thyroid problems, such as hypothyroidism.
These symptoms can vary in severity and not all people with Down syndrome will experience the same symptoms. Early intervention, specialized education and supportive care can help individuals with Down syndrome manage their symptoms and reach their full potential.
Cognitive Development of people with Down Syndrome
Children with Down Syndrome may experience delays in cognitive development, but they still have the ability to learn, grow, and develop their intellectual abilities. Cognitive development encompasses various areas, including language, memory, attention, perception, and problem solving.
Language: Children with Down Syndrome typically develop language at a slower pace compared to their peers. However, they can still learn to communicate effectively through speech and/or sign language. It’s important to provide a supportive environment that encourages language development, such as talking to the child regularly and reading books together.
Memory: Children with Down Syndrome may have difficulty with short-term memory, but they can still learn and retain information over time with the help of repetition and organization. Parents and caregivers can support memory development by using memory aids, such as visual aids, and engaging in memory games and activities.
Attention: Children with Down Syndrome can have attention difficulties, but with the right support and interventions, they can improve their ability to focus and pay attention. It’s important to limit distractions and provide structure and routine to help the child stay focused.
Perception: Children with Down Syndrome may have difficulty processing information from their senses, such as sight, hearing, touch, and taste. They may need support to understand their environment and interact with others effectively.
Problem Solving: Children with Down Syndrome may experience delays in problem solving, but with the right support and interventions, they can learn to solve problems and make decisions. It’s important to provide opportunities for the child to practice problem solving, such as through puzzles and games.
Physical Development of people with Down Syndrome
Physical development is another important aspect of growth and development for children with Down Syndrome. Physical development encompasses areas such as motor skills, coordination, and dexterity.
Motor Skills: Children with Down Syndrome may have difficulty with gross motor skills, such as crawling, walking, and jumping, but with the right support and interventions, they can improve their motor skills over time. Physical therapy and exercises can help to improve muscle strength and coordination.
Coordination: Children with Down Syndrome may have difficulty with fine motor skills, such as writing and manipulating small objects, but with the right support and interventions, they can improve their coordination. Occupational therapy and exercises can help to improve dexterity and hand-eye coordination.
Dexterity: Children with Down Syndrome may have difficulty with hand dexterity, but with the right support and interventions, they can improve their ability to manipulate objects and perform daily activities. Occupational therapy and exercises can help to improve hand strength and dexterity.
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