What causes Down syndrome?
This genetic/chromosomal condition is caused by the presence of a full or partial extra copy of the 21st chromosome. This extra genetic material changes the overall course of development for the individual's brain and body, leaving them with the physical and intellectual characteristics of Down syndrome.
There are three types of Down syndrome:
Trisomy 21 (Nondisjunction)
There are three types of Down syndrome:
Trisomy 21 (Nondisjunction)
- This is the most common form of Down syndrome, accounting for 95% of all Down syndrome diagnoses. This occurs when an individual has an extra copy of chromosome 21. While normally individuals are born with two copies of chromosome 21, individuals with Trisomy 21 or Nondisjunction Down syndrome have three copies of this chromosome. This extra chromosome is replicated within every cell of the body, and all cells are now made up of 47 chromosomes due to the extra copy of chromosome 21.
- This form of Down syndrome accounts for 4% of all diagnoses. Translocation occurs when a full or partial extra copy of the 21st chromosome becomes attached to another chromosome within the cell.
- Being the least common form of Down syndrome, Mosaicism accounts for just 1% of all cases. This occurs when cell make-up is inconsistent. Some cells contain 46 chromosomes (normal), while others are made up of 47 chromosomes. Those cells that are made up of 47 chromosomes contain the extra full or partial copy of chromosome 21.
Risk Factors
Maternal Age
- The risk of having a child with Down syndrome increases with maternal age
- At age 25 = 1 in 1,200
- At age 30 = 1 in 900
- At age 35 = 1 in 350
- At age 40 = 1 in 100
- At age 45 = 1 in 30
- As couples delay marriage and parenting the rate of children born with Down syndrome is expected to increase.
- Having one child with down syndrome increases your chances (up to 1 in 100) of having a second child with Down syndrome.
- Heredity does not play a factor in the prevalence of Trisomy 21 or Mosaicism. However 1/3 of translocation diagnoses can be traced back to heredity. Overall, heredity accounts for just 1% of all Down syndrome cases.
Diagnosis
Prenatally
- Prenatal screenings provide the probability/chance that the fetus/child will have Down syndrome.
- Blood samples are taken from the mother to identify substances in the blood, such as the chromosomal material present.
- Blood tests are usually done in combination with sonograms to identify markers or characteristics of Down syndrome present with the fetus.
- Prenatal screenings are accurate but are not definite or entirely conclusive
- Diagnostics/Diagnostic Procedures
- Chorionic Villus Sampling (CVS) is performed between the 9th and 14th weeks of pregnancy and tests the cells present in the placenta in order to detect birth defects, genetic disease, and other problems with the fetus during pregnancy.
- Amniocentesis can be performed between the 15th and 20th weeks of pregnancy. Birth defects are detected through the testing of amniotic fluid.
- These tests are nearly 100% accurate in diagnosing Down syndrome, however there is a small risk (1%) of causing a miscarriage.
- At birth, certain physical characteristics associated with Down syndrome can be identified.
- If it is determined that the child may have Down syndrome, a Karyotype analysis will be performed.
- Karyotype analyses examine and group together the child's chromosomes, through a blood sample, to conclusively identify the presence of Down syndrome.
- A FISH test (Fluorescence in situ hybridization) may also be conducted. This test maps the genes and portions of genes that are present in cells. This test can be conducted and completed in a shorter amount of time.
Symptoms of Down syndrome
- Short stature/height
- Low muscle tone (Hypotonia)
- Short, wide neck
- Short, stocky arms & legs
- Single deep crease across the center of the palm
- Upward slanted eyes
- Flat nasal bridge
- Small ears
- Irregular shaped mouth & tongue
- Irregular and/or crooked teeth
Health Problems/Complications
Individuals with Down syndrome are at a higher risk of developing/experiencing a variety of health problems. These health problems can arise as a result of abnormally developed body structures and include:
- Heart defects & Heart Disease
- Hypothyroidism
- Respiratory Infections
- Impaired immune system
- Hearing problems (which can impact listening skills & language development)
- Problems with sight/eyes
- Dental problems/Gum Disease (Periodontal Disease)
- Seizures
- Sleep problems (sleep apnea & difficulty falling/staying asleep)
- Unstable joints, weak ligaments, and poor muscle strength that can lead to spinal, neck, and foot injuries/problems
- Skin conditions and infections
- Digestive problems including Celiac disease & constipation/intestinal blockage
- Hirschsprung disease
- Lymphoma
- Reflux (GERD)
- Dementia
- Depression, anxiety, and other mental health/behavior issues
Life Expectancy
Nearly 100 years ago, the average individual with Down syndrome was expected to live until just age nine. However, with advancements in the medical field, especially with treatment options for the medial issues that arise due to the condition, individuals with Down syndrome are now expected to live until age 60, however many are surpassing this number!
References:
Coppus, A. (2013). People with intellectual disability: What do we know about adulthood and life expectancy?. Developmental Disabilities Research Reviews, 18(1), 6-16.
Down Syndrome - Symptoms, Causes, Diagnosis and Treatment - from WebMD. (n.d.).
Retrieved November 2, 2016, from http://www.webmd.com/children/tc/down-syndrome-topic-overview#1
De Jong, A., & de Wert, G. (2015). Prenatal screening: an ethical agenda for the near future. Bioethics, 29(1), 46-55.
Heslam, S. (2011). Health issues for adults with Down's syndrome. Learning Disability Practice, 14(6), 26-27.
Mayo Clinic. (n.d.). Down syndrome. Retrieved November 2, 2016, from
http://www.mayoclinic.org/diseases-conditions/down-syndrome/basics/definition/con-20020948
Mills, S., & Black, L. (2014). Ensuring children with Down's syndrome reach their full potential. British Journal Of School
Nursing, 9(2), 97-99.
National Down Syndrome Society. (n.d.). What Is Down Syndrome? Retrieved November 2,
2016, from http://www.ndss.org/down-syndrome/what-is-down-syndrome/
*Photo references listed below
Coppus, A. (2013). People with intellectual disability: What do we know about adulthood and life expectancy?. Developmental Disabilities Research Reviews, 18(1), 6-16.
Down Syndrome - Symptoms, Causes, Diagnosis and Treatment - from WebMD. (n.d.).
Retrieved November 2, 2016, from http://www.webmd.com/children/tc/down-syndrome-topic-overview#1
De Jong, A., & de Wert, G. (2015). Prenatal screening: an ethical agenda for the near future. Bioethics, 29(1), 46-55.
Heslam, S. (2011). Health issues for adults with Down's syndrome. Learning Disability Practice, 14(6), 26-27.
Mayo Clinic. (n.d.). Down syndrome. Retrieved November 2, 2016, from
http://www.mayoclinic.org/diseases-conditions/down-syndrome/basics/definition/con-20020948
Mills, S., & Black, L. (2014). Ensuring children with Down's syndrome reach their full potential. British Journal Of School
Nursing, 9(2), 97-99.
National Down Syndrome Society. (n.d.). What Is Down Syndrome? Retrieved November 2,
2016, from http://www.ndss.org/down-syndrome/what-is-down-syndrome/
*Photo references listed below