Down syndrome is one of the most common genetic disorders and one that we, as a general public, know so little about!
It is the perfect time to find out more things about it!
- Down syndrome is also known as trisomy 21
- It is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21
- It is typically associated with physical growth delays
- Mild to moderate intellectual disability
- And characteristic facial features
- The average IQ of a young adult with Down syndrome is 50
- Equivalent to the mental ability of an 8- or 9-year-old child
- But this can vary widely
- The parents of the affected individual are typically genetically normal
- The probability increases from less than 0.1% in 20-year-old mothers to 3% in those of age 45
- The extra chromosome is believed to occur by chance
- With no known behavioral activity or environmental factor that changes the probability
- Down syndrome can be identified during pregnancy by prenatal screening followed by diagnostic testing
- Or after birth by direct observation and genetic testing
- Since the introduction of screening, pregnancies with the diagnosis are often terminated
- Regular screening for health problems common in Down syndrome is recommended throughout the person’s life
- There is no cure for Down syndrome
- Education and proper care have been shown to improve quality of life
- Some children with Down syndrome are educated in typical school classes
- While others require more specialized education
- Some individuals with Down syndrome graduate from high school
- And a few attend post-secondary education
- In adulthood, about 20% in the United States do paid work in some capacity
- With many requiring a sheltered work environment
- Support in financial and legal matters is often needed
- Life expectancy is around 50 to 60 years in the developed world with proper health care
- Down syndrome is one of the most common chromosome abnormalities in humans
- It occurs in about one per 1,000 babies born each year
- In 2015, Down syndrome was present in 5.4 million individuals globally
- And resulted in 27,000 deaths
- Down from 43,000 deaths in 1990
- It is named after John Langdon Down
- A British doctor who fully described the syndrome in 1866
- Some aspects of the condition were described earlier by Jean-Étienne Dominique Esquirol in 1838 and Édouard Séguin in 1844
- In 1959, the genetic cause of Down syndrome, an extra copy of chromosome 21, was discovered
- Those with Down syndrome nearly always have physical and intellectual disabilities
- As adults, their mental abilities are typically similar to those of an 8- or 9-year-old
- They also typically have poor immune function
- And generally reach developmental milestones at a later age
- They have an increased risk of a number of other health problems
- Including congenital heart defect, epilepsy, leukemia, thyroid diseases, and mental disorders
- People with Down syndrome may have some or all of these physical characteristics
- A small chin, slanted eyes, poor muscle tone, a flat nasal bridge, a single crease of the palm, and a protruding tongue due to a small mouth and relatively large tongue
- These airway changes lead to obstructive sleep apnea in around half of those with Down syndrome
- Other common features include: a flat and wide face, a short neck, excessive joint flexibility, extra space between big toe and second toe, abnormal patterns on the fingertips and short fingers
- Instability of the atlantoaxial joint occurs in about 20% and may lead to spinal cord injury in 1- 2%
- Hip dislocations may occur without trauma in up to a third of people with Down syndrome
- Growth in height is slower, resulting in adults who tend to have short stature
- The average height for men is 154 cm (5 ft 1 in) and for women is 142 cm (4 ft 8 in)
- Individuals with Down syndrome are at increased risk for obesity as they age
- Growth charts have been developed specifically for children with Down syndrome
- This syndrome causes about a third of cases of intellectual disability
- Many developmental milestones are delayed with the ability to crawl typically occurring around 8 months rather than 5 months
- And the ability to walk independently typically occurring around 21 months rather than 14 months
- Most individuals with Down syndrome have mild or moderate intellectual disability
- With some cases having severe difficulties
- Those with mosaic Down syndrome typically have IQ scores 10- 30 points higher
- As they age, people with Down syndrome typically perform worse than their same-age peers
- Commonly, individuals with Down syndrome have better language understanding than ability to speak
- Between 10 and 45% have either a stutter or rapid and irregular speech
- Making it difficult to understand them
- Some after 30 years of age may lose their ability to speak
- They typically do fairly well with social skills
- Behavior problems are not generally as great an issue as in other syndromes associated with intellectual disability
- In children with Down syndrome, mental illness occurs in nearly 30% with autism occurring in 5- 10%
- People with Down syndrome experience a wide range of emotions
- While people with Down syndrome are generally happy
- Symptoms of depression and anxiety may develop in early adulthood
- Children and adults with Down syndrome are at increased risk of epileptic seizures
- Which occur in 5- 10% of children and up to 50% of adults
- This includes an increased risk of a specific type of seizure called infantile spasms
- Many (15%) who live 40 years or longer develop Alzheimer disease
- In those who reach 60 years of age, 50- 70% have the disease
- Hearing and vision disorders occur in more than half of people with Down syndrome
- Vision problems occur in 38 to 80%
- Between 20 and 50% have strabismus, in which the two eyes do not move together
- Cataracts occur in 15%
- And may be present at birth
- Keratoconus (a thin, cone-shaped cornea) and glaucoma (increased eye pressure) are also more common
- As are refractive errors requiring glasses or contacts
- Brushfield spots (small white or grayish/brown spots on the outer part of the iris) are present in 38 to 85% of individuals
- Hearing problems are found in 50–90% of children with Down syndrome
- This is often the result of otitis media with effusion which occurs in 50–70%
- And chronic ear infections which occur in 40 to 60%
- Down syndrome is caused by having three copies of the genes on chromosome 21
- Rather than the usual two
- The parents of the affected individual are typically genetically normal
- Those who have one child with Down syndrome have about a 1% risk of having a second child with the syndrome
- If both parents are found to have normal karyotypes
- The extra chromosome content can arise through several different ways
- The most common cause is a complete extra copy of chromosome 21, resulting in trisomy 21
- In 1.0 to 2.5% of cases, some of the cells in the body are normal and others have trisomy 21
- Known as mosaic Down syndrome
- The other common mechanisms that can give rise to Down syndrome include: a Robertsonian translocation, isochromosome, or ring chromosome
- These contain additional material from chromosome 21 and occur in about 2.5% of cases
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